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A 

SYSTEM  OF  INSTRUCTION 

IN 


QUANTITATIVE  CHEMICAL  ANALYSIS. 


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CHEMICAL  ISTOTA.TIOiN' 


AND 

NOMENCLATURE, 

OLD  AND  NEW. 


Beginners  in  Chemistry  are  liable  to  much  confusion  and  em- 
barrassment from  the  fact  that  there  are  now  in  use  two  distinct 
systems  of  Chemical  Notation  and  several  forms  of  Nomenclature. 

The  older  chemistry — the  chemistry  generally  in  vogue  up  to 
1860,  and  still  employed  in  all  the  best  treatises  on  technical,  an- 
alytical, physiological  and  pharmaceutical  chemistry — differs  from 
the  “ modern  chemistry,”  primarily,  in  so  tar  as  notation  is  con- 
cerned, in  the  use  of  different  atomic  weights  for  certain  elements. 
The  older  atomic  weights  employed  by  English  writers  were  de- 
cided upon  from  narrow  grounds,  and  somewhat  arbitrarily.  It 
^having  been  found,  for  example,  that  water  contains  one  part  by 
^ weight  of  hydrogen  to  eight  parts  by  weight  of  oxygen,  the  atomic 
weight  of  oxygen  was  assumed  to  be  eight  times  that  of  hydrogen, 
and  water  was  assumed  to  consist  of  one  atom  of  each  element, 
and  had  the  symbol  HO  assigned  to  it.  Carbonic  oxide  was 
found  to  contain  six  weights  of  carbon  to  eight  weights  of  oxy- 
gen, and  being  the  oxygen  compound  in  which  the  least  quantity 
of  carbon  exists,  was  therefore  assumed  to  contain  one  atom  of 
each  of  its  elements,  and  six  became  accordingly  the  atomic 
O weight  of  carbon.  Carbonic  acid,  with  double  the  proportion  of 
S-  oxygen,  was  considered  to  contain  two  atoms  of  oxygen  and  was 
. written  COa.  As  discovery  revealed  the  composition  of  bodies, 
their  atomic  weights  were  agreed  upon  with  reference  only  to  ap- 
pt  parent  simplicity  and  harmony  to  what  had  been  previously  as- 
* sumed,  in  the  absence  of  any  other  and  more  philosophical  crite- 
y,  rion  or  guide. 

The  atomic  theory  of  Dalton  was  and  still  is  philosophical,  be- 
cause it  gives,  in  a certain  sense,  a reason  for  the  laws  of  definite 
and  multiple  combination  ; but  the  atomic  weights  he  and  his  suc- 


* 

d 


217588 


cessors  adopted  were  open  to  revision,*  the  simplicity  which  was 
relied  upon  in  selecting  them  being  often  more  apparent  than 
real.  Thus  the  atomic  weight  of  carbon  was  taken  to  be  the 
smallest  quantity  of  that  element  which  would  unite  with  oxy- 
gen. Had  it  happened  that  carbonic  oxide  was  then  unknown, 
and  that  carbonic  acid  was  believed  to  be  the  lowest  oxide  of 
carbon,  the  atomic  weight  of  carbon  would  have  been  fixed  at  3, 
oxygen  being  8.  Or,  if  the  atomic  weight  of  carbon  had  been 
measured  directly  by  hydrogen,  in  the  lowest  hydride  of  carbon, 
marsh  gas,  assumed  to  be  CH2,  the  result  would  also  have  been 
3.  We  see,  then,  evidently,  that  the  formerly  received  atomic 
weights  of  those  elements,  which  form  multiple  combinations, 
were  liable  to  be  multiples  or  divisors  of  the  true  f atomic 
weights,  and  were,  of  necessity,  thus  far  arbitrarily  chosen. 

The  discovery  that  the  volumes  in  which  gases  unite  bear  sim 
pie  ratios  to  one  another,  was  regarded  as  a clue  which  might 
point  with  certainty  to  the  real  atomic  relations.  When  two 
volumes  of  water  vapor  are  decomposed,  there  result  two  volumes 
of  hydrogen  and  one  volume  of  oxygen.  Berzelius  did  not  hesi- 
tate to  declare  his  belief  that  the  number  of  volumes  repre- 
sent the  number  of  atoms ; that,  accordingly,  water  is  a com- 
pound of  two  atoms  of  hydrogen  with  one  atom  of  oxygen ; that 
its  formula  is,  therefore,  H20 ; and  that  the  atomic  weight  of 
hydrogen  being  one,  that  of  oxygen  must  be  sixteen,  or  double 
what  Dalton  assumed. 

The  progress  of  science  has  gradually  brought  the  minds  of 
chemists  to  the  conviction  that  the  greater  number  of  the  old 
atomic  weights  must  be  doubled,  and  that  certain  formulae  must 
be  changed  accordingly.  To  this  result  not  only  the  u law  of  vol- 
umes,” but  a comparison  of  the  specific  heats  of  the  elements  and 
other  physical  considerations  have  contributed,  while  purely  chem- 
ical reasons  furnish  the  most  conclusive  arguments  in  favor  of 
the  change. 

The  fact  that  the  older  atomic  weights  and  nomenclature  have 
been  so  long  in  use  among  druggists,  physicians,  and  manufac- 
turers, and  that  so  vast  a mass  of  chemical  literature  has  been 
written  in  accordance  with  them,  lias  properly  enough  prevented 
their  sudden  abandonment.  The  greater  truth  of  the  modern 
chemistry  must  ultimately  compel  its  adoption  with  more  or  less 
modifications.  For  the  present  it  is  important  that  the  student 
become  familiar  with  both.  This  familiarity  can  readily  be  ac- 
quired by  practice  in  translating  the  older  symbols  into  the  newer, 
and  the  reverse,  by  aid  of  the  rules  to  be  found  below. 

In  modern  chemistry  the  idea  of  quantivalence  or  atom-fixing 
power  serves  a very  important  part.  Those  elements  which,  like 
chlorine,  unite  with  h}7drogen,  volume  for  volume,  i.e.,  atom  for 


* Independently  of  errors  in  their  determination  as  combining  Veights. 
f Assuming  the  Atomic  Theory  to  be  an  expression  of  fact. 


3 


atom,  have  been  termed  monads,  or  have  been  characterized  as 
univalent  (one-value)  elements.  Those  elements  which,  like 
oxygen,  combine  with  twice  their  volume  (or  two  atoms)  of 
hydrogen  or  other  monad  radical,  are  dyads,  and  are  spoken  of  as 
bivalent  (two-value)  radicals.  Triads,  tetrads,  pentads,  and  hexads 
are  elements  (or  radicals)  which  unite  respectively  with  three, 
four,  five,  and  six  times  their  (gaseous)  volume  of  hydrogen  or 
analogous  monads,  and  to  which  apply  respectively  the  adjectives 
tri valent,  quadrivalent,  quinquivalent,  and  sexivalent. 

Those  elements  whose  quantivalence  is  expressed  by  an  odd 
number,  1,  3,  5 or  7,  are  collectively  termed  perissads , and  those 
which  unite  with  an  even  number  of  atoms  of  hydrogen  or 
chlorine  are  designated  artiads .* 

The  following  table  gives  the  two  systems  of  atomic  weights, 
the  older  following  the  symbol  printed  in  Koman  type,  and  the 
newer  that  printed  in  Italics. 


PERISSADS. 

ARTIADS. 

ODD  AND 

NEW 

OLD 

NEW 

MONADS.  ATOMIC  WEIGHTS. 

DYADS. 

AT.  WTS. 

AT.  WTS. 

Hydrogen, 

H = 

1 

Oxygen, 

0=8 

0 = 

16 

Chlorine, 

Cl  = 

35.5 

Sulphur, 

S = 16 

s = 

32 

Bromine, 

Br  = 

80 

Selenium, 

Se=  39.5 

Se  = 

79 

Iodine, 

I = 

127 

Tellurium, 

Te=  64 

Te  = 

128 

Fluorine, 

F = 

19 

Calcium, 

Ca=  20 

Ca  = 

40 

Lithium, 

Li  = 

7 

Strontium, 

Sr  = 43.75  Sr  = 

87.5 

Sodium, 

Na  = 

23 

Barium, 

Ba=  68.5 

Ba  = 

137 

Potassium, 

K = 

39 

Mercury, 

Hg  = 100 

200 

Rubidium, 

Rb  = 

85.4 

Copper, 

Cu=  31.7 

Cu  = 

63.4 

Caesium, 

Cs  = 

133 

Lead, 

Pb  = 103.5 

Pb  = 

207 

Thallium, 

T1  = 

203 

Cadmium, 

Cd  = 56 

Cd  = 

112 

Silver, 

Ag  = 

108 

Zinc, 

Zn  = 32.5 

Zn  = 

65 

Magnesium, 

Mg  = 2 

Mg  = 

24 

TRIADS. 

Boron, 

B = 

11 

TETRADS. 

Gold, 

Au  = 

19f> 

Carbon, 

C = 6 

C = 

12 

Silicon 

Si  = 14 

Si  = 

28 

PENTADS. 

Titanium, 

Ti  = 25 

Ti  = 

50 

Nitrogen, 

N = 

14 

Tin, 

Sn  = 59 

Sn  = 

118 

Phosphorus, 

P = 

31 

Aluminium, 

A1  =13.75 

Al  = 

27.5 

Arsenic, 

As  == 

75 

Platinum, 

Pt  = 98.94 

Pt  = 

197.88 

Antimony, 

Sb  = 

122 

Palladium, 

Pd  = 53 

Pd  = 

106 

Bismuth, 

Bi  = 

210 

Vanadium, 

V = 

51.3 

HEXADS. 

Chromium, 

Cr  = 26.25 

Cr  = 

52.5 

Manganese, 

Mn  = 27.5 

Mn  = 

55 

Iron, 

Fe  = 28 

Fe  = 

56 

Nickel, 

Ni  = 29.5 

Ni  = 

59 

Cobalt, 

Co  = 9.5 

Co  = 

59 

Uranium, 

U = 59.4 

U = 

118.8 

Molybdenum,  Mo  = 46 

Mo  = 

92 

* Chemists  are  not  agreed  as  to  the  quantivalence  of  various  elements. 

Some 

regard  sulphur  as  a hexad,  and  others  put  down  iron,  cobalt,  and  some  other 
metals  as  dyads.  Wanklyn  considers  sodium  to  be  a triad.  The  distinction  be- 
tween perissads  and  artiads  is  more  absolute,  but  certain  elements,  especially 
Vanadium  and  Uranium,  may  be  put  in  both  groups. 


4 


It  will  be  seen  from  the  above  table  that  the  atomic  weights  of 
the  so-called  perissad  elements,  including  the  monads  hydrogen, 
chlorine,  and  the  members  of  its  group,  the  alkali  metals,  thallium 
and  silver,  the  triads  boron  and  gold,  and  the  pentads  nitrogen, 
etc.,  including  bismuth,  have  the  same  atomic  weights  in  the 
newer  chemistry  as  have  been  so  long  used  in  the  older. 

On  the  contrary,  the  artiad  elements,  viz.,  the  dyads  oxygen, 
sulphur,  selenium,  tellurium,  and  the  alkali  earth-metals  ; the 
tetrads  carbon,  silicon,  titanium,  tin,  and  the  remaining  metallic 
elements  which  are  dyads,  tetrads,  or  hexads,  have  double  the 
atomic  weights  in  the  new  system  which  they  had  in  the  old. 

To  convert  the  old-system  formul£e  into  corresponding  values 
of  the  new,  the  following  rules  are  indicated  : — 

1.  Compounds  of  perissad  elements. — The  symbols  of  compounds 
of  perissad  elements  are  ordinarily  alike  in  both  systems,  and  their 
values,  expressed  by  the  atomic  weights  of  the  old  system,  or 
by  the  molecular  weights  of  the  new  system,  are  the  same 
in  both.  viz.  : — 


ATOMTC  WEIGHT.  MOLECULAR  WEIGHT. 

OLD  SYSTEM.  NEW  SYSTEM. 


SYMBOLS. 

V y 

HC1 

36.5 

nh3 

17 

PC16 

208.5 

bf3 

68 

If  the  newer  symbols  are  unlike  the  old,  the  latter  and  their 
values  are  multiplied  to  make  the  new.  Some  chemists  change 
the  symbols  of  the  liquid  and  solid  phosphides  of  hydrogen, 
viz.: — 


GAS. 

AT.  WT, 

LIQUID. 

AT.  WT. 

SOLID. 

AT.  WT. 

Old  system 

..  H3P 

34 

: H,P 

33  : 

hp2 

63 

MOL.  WT. 

MOL.  WT. 

MOL.  WT. 

New  system 

. . II3P 

34 

: H4P2 

66  : 

h2p4 

126 

2.  Compounds  of  artiad  elements. — The  symbols  of  compounds 
of  artiad  elements  are  commonly  alike  in  both  systems,  but  in 
the  new  system  the  values  are  double  those  of  the  old. 


SYMBOLS. 

ATOMIC  WEIGHT. 
OLD  SYSTEM. 

MOLECULAR  WEIGHT. 
NEW  SYSTEM. 

S02 

32 

64 

CO 

14 

28 

C02 

22 

44 

BaO 

76.5 

153 

FeS 

44 

88 

Al.Os 

51.5 

103 

Ba05S0s=BaS04 

116.5 

233 

3.  Compounds  of  perissad  with  artiad  elements. — The  symbols 
of  compounds  of  perissad  with  artiad  elements  are  converted  from 
the  old  into  the  new  system,  generally,  by  halving  the  number  of 


5 


artiad  atoms,  in  which  case  the  values  are  the  same  in  both 
systems,  viz. : — 


SYMBOLS. 


OLD  SYSTEM.  NEW  SYSTEM. 

jST.aOHO  NaHO 

Cr,Os,3  S03,  K0S03,24H0  Cr(S04)2K.12H20* 

HONOs  HN03 

KOCO,,  H0C02  KHCO3 

C102H9bOJ2  (C3H5)  (0lBH3,0,)*t 


VALUES. 

OLD  AT.  WT.  AND  NEW  MOL.  WT. 

40 

499.5 

63 

100 

80G 


When  the  number  of  artiad  atoms  cannot  be  halved,  and  in 
some  other  cases,  the  number  of  perissad  atoms  is  doubled,  the 
values  being  doubled  at  the  same  time,  viz. : — 

SYMBOLS.  VALUES. 


OLD  SYSTEM. 

no5 

NEW  SYSTEM. 

n2o5 

OLD  AT.  WT. 

54 

NEW  MOL.  WT. 
108 

HO 

h2o 

9 

18 

CaCl 

CaCl2 

55.5 

111 

HgCl 

Hg.2Cl2 

235.5 

771 

HgCl 

HgCl2 

135.5 

271 

BaO.HO 

BaH202 

85.5 

171 

Cr203,3S03,K0,S03 

24HO 

K2Cr.08(S02)4 

24H20t 

499.5 

999 

The  form  and  arrangement  of  the  symbols  of  complicated  com- 
pounds is  very  various,  and  can  only  be  learned  by  study  of  the 
masters  who  lead  usage.  As  regards  nomenclature  the  “modern ” 
chemists  are  by  no  means  agreed.  The  departures  from  traditional 
English  usage  are,  however,  with  few  exceptions,  simple  changes 
of  verbal  form,  such  as  zinc  sulphate  or  zincic  sulphate  instead  of 
sulphate  of  zinc,  lead  nitrite  or  plumbic  nitrite  instead  of  nitrite 
of  lead,  silver  chloride  or  argentic  chloride  instead  of  chloride 
of  silver. 

In  case  of  the  oxygen  compounds  of  the  alkali  and  alkali-earth 
metals,  the  name  of  the  metal  itself  and  not  that  of  the  oxide  is 
used,  viz. : calcium  sulphate  or  calcic  sulphate  instead  of  sulphate 
of  lime,  sodium  borate  or  sodic  borate  instead  of  borate  of  soda, 
barium  nitrate  or  baric  nitrate  rather  than  nitrate  of  baryta. 

In  case  of  the  metals  which  have  two  basic  oxides,  these  and 
the  corresponding  salts  are  distinguished  by  the  particles  ous  and 
ic  affixed  to  the  name  of  the  metal  used  adjectively ; thus,  protoxide 
of  iron  and  sesquioxide  or  peroxide  of  iron  are  respectively  ferrous 
and  ferric  oxide,  hydrated  protoxide  is  ferrous  hydrate,  sesqui- 
sulphate  is  ferric  sulphate.  Similarly,  we  have  cuprous  acetate, 
cupric  oxide,  mercurous  nitrate,  and  mercuric  phosphate.  So 
aluminic  sulphate  (by  analogy),  nickelous  oxalate,  bismuthic  bro- 
mide, &c. 


* Chrome  alum,  Watts. 
f Tripalmitine. 
f Chrome  Alum,  COOKS. 


6 


It  has  long  been  conceded  that  the  traditional  acids  C02,  SOs, 
POB(.P206),  ~NOb(JVfi6)  &c.,  are  no  acids  (i.e.,  sour  bodies)  at  all, 
but  yield  acids  by  their  combination  with  the  elements  of  water. 
They  were  therefore  termed  anhydrous  acids.  Later  they  have 
been  classed  together  as  anhydrides  and  designated  individually 
as  carbonic  anhydride,  sulphuric  anhydride,  phosphoric  anhy- 
dride, &c.,  and  this  nomenclature  is  now  employed  by  many 
chemists,  especially  by  Odling  and  Frankland.  Others,  fol- 
lowing Williamson,  insist  that  CO„  SO^,  &c.,  are  acids  in  the 
sense  of  the  old  nomenclature,  and  retain  for  them  the  old  names, 
while  the  sour  (hydrated)  acids  are  designated  as  hydrogen  or 
hydric  salts,  viz.:  i/2$6>4=:hydric  sulphate,  IlfiO^—hy^vio,  phos- 
phate or  phosphoric  hydrate.  Still  other  chemists  prefer  to 
fall  back  upon  numeral  prefixes  in  case  of  the  anhydrides  and  other 
related  oxides,  viz. : Watts  gives  to  CO,CO„  and  Clfi^  the  names 
carbon  monoxide,  carbon  dioxide,  and  chlorine  tetroxide.  Poscoe 
makes  CO  carbonic  oxide,  CO 2 carbonic  dioxide,  and  ClfiK  chlo- 
ric tetroxide. 

In  case  of  bodies  of  more  complicated  composition,  especially 
those  belonging  to  organic  chemistry,  the  assumption  of  compound 
radicals  or  other  peculiar  views  of  rational  constitution  have  led 
chemists  to  construct  various  new  formulae  and  corresponding 
new  names,  which  are  to  be  learned  in  the  writings  where  they 
are  propounded. 


A 


SYSTEM  OF  INSTRUCTION 


IN 


QUANTITATIVE  CHEMICAL 
ANALYSIS. 

V/ 

{y  BY  * 

DR.  C.  REMIGIUS  FRESENIUS, 

PROFESSOR  OF  CHEMISTRY  AND  NATURAE  PHILOSOPHY,  WIESBADEN. 


jfrom  lf)je  last  anb  (fixjtrmait  ESMtions. 


EDITED  BY 

SAMUEL  W.  JOHNSON,  M.A., 

PROFESSOR  OF  ANALYTICAL  AND  AGRICULTURAL  CHEMISTRY  IN  THE  SHEFFIELD  SCIENTIFIC 
SCHOOL,  YALE  COLLEGE. 


NEW  YORK: 

JOHN  WILEY  & SON, 

2 CLINTON  HALL,  ASTOR  PLACE. 

1871. 


Entered  according  to  Act  of  Congress,  in  the  year  1870,  by 
JOHN  WILEY, 

In  the  Clerk’s  Office  of  the  District  Court  of  the  United  States  for  the  Southern 
District  of  New  York. 


The  New  York  Printing  Company, 

8i,  83,  and  85  Centre  Street , 

New  York. 


EDITOR’S  PREFACE. 


In  preparing  this  edition  of  Fresenius’  Quantitative  Chemical 
Analysis,  the  editor  has  sought  by  various  changes  to  adapt  it  to 
the  wants  of  the  American  student. 

The  foreign  editions  have  attained  such  encyclopedic  dimensions 
as  to  occasion  the  beginner  no  little  confusion  and  embarrassment. 
For  this  reason  the  bulk  of  the  work  has  been  considerably  re- 
duced. A few  processes  which  the  editor’s  experience  has  con- 
vinced him  are  untrustworthy,  and  many  more  that  can  well  be 
spared  because  they  are  tedious  or  unnecessary,  have  been  omit- 
ted. The  entire  chapter  on  Analysis  of  Mineral  Waters,  excellent 
as  it  is,  has  been  suppressed  on  account  of  its  length,  and  because 
the  few  who  have  occasion  to  make  detailed  investigations  in  that 
direction  have  access  to  the  original  sources  of  information. 

The  section  on  Organic  Analysis  has  been  reduced  from  sixty  to 
thirty  pages,  mainly  by  the  omission  of  processes  which  from  their 
antiquity  or  inferiority  are  more  curious  than  useful.  The  chap- 
ters on  Acidimetry  and  Alkalimetry  have  been  likewise  greatly 
condensed,  and  all  that  especially  relates  to  Soils  and  Ashes  of 
Plants  has  been  left  out.  The  recent  appearance  of  an  excellent 
special  treatise  on  “Agricultural  Chemical  Analysis,”  by  Profes- 
sor Caldwell,  of  Cornell  University,  justifies  the  last-named 
omission. 

On  the  other  hand,  some  important  matter  has  been  added. 
Bunsen’s  invaluable  new  methods  of  treating  precipitates  are  de- 
scribed in  his  own  (translated)  words.  Various  new  methods  of 
estimation  and  separation  are  incorporated  in  their  proper  places. 

The  editor  thankfully  acknowledges  his  indebtedness  to  several 
gentlemen  for  special  contributions  to  this  work;  viz. : To  Dr.  J. 
Lawrence  Smith,  who  has  kindly  furnished  a manuscript  account 
of  his  admirable  method  of  fluxing  silicates  for  the  estimation  of 
alkalies.  To  O.  D.  Allen,  Esq.,  late  chemist  to  the  Freedom  Iron 


vi 


editor’s  preface. 


Works,  Lewistown,  Pennsylvania,  for  copious  notes  of  his  exten- 
sive experience  in  the  analyses  of  steel,  iron,  and  iron  ores,  which 
have  been  freely  employed  in  §229.  To  Mr.  Wm.  G.  Mixter, 
chief  assistant  in  the  Sheffield  Laboratory,  for  the  account  of  the 
gold  and  silver  assay.  To  Professor  Brush,  of  Yale  College,  Pro- 
fessor Collier,  of  Term  on  t University,  and  B.  S.  Burton,  Esq.,  of 
Philadelphia,  for  various  important  facts  and  suggestions*  Just 
before  going  to  press,  Dr.  Wolcott  Gibbs  has  communicated  an 
account  of  his  new  method  of  finding  at  once  the  total  correction 
for  temperature,  pressure  and  moisture  in  absolute  determinations 
of  nitrogen  or  other  gases,  which,  from  its  simplicity,  convenience, 
and  accuracy  must  prove  of  the  highest  service  to  chemistry.  It 
will  be  found,  with  some  other  matters,*  in  an  appendix,  p.  619. 

The  additions  which  have  been  made  to  the  methods  of  exam- 
ining ores,  it  is  believed,  adapt  the  work  to  meet  all  the  ordinary 
requirements  of  the  metallurgical  and  mining  student. 

The  editor’s  additions  are  distinguished,  in  all  important  cases, 
by  enclosure  in  brackets,  [ ]. 

While  fully  recognizing  the  necessity  of  teaching  the  new 
notation  and  nomenclature  of  chemistry,  the  editor  has  in  this 
book  retained  the  old  system,  because  it  is  identified  with  the 
chemical  literature  of  the  century,  and  cannot  be  speedily  for- 
gotten by  practical  men.  At  a time  when  the  most  elementary 
text-books  are  framed  on  the  “modern  ” system,  it  is  important 
to  keep  the  student  exercised  in  the  language  of  the  old  masters 
of  the  science,  which  is  still,  and  must  for  some  time  remain,  a 
part  of  the  vernacular  of  the  physician,  the  apothecary,  the 
metallurgist,  and  the  manufacturer. 

SAMUEL  W.  JOHNSON. 

Sheffield  Laboratory  of  Yale  College,  Dec.,  1869. 


* Viz.,  assay  of  chrome  iron,  and  separation  of  phosphoric  acid  from  lime, 
alumina,  and  iron. 


CONTENTS 


PAGE 

Introduction . 1 

PART  I. 

GJ-EHSTER^IL.  PART. 

DIVISION  L 

EXECUTION  OF  ANALYSIS. 

SECTION  I. 

Operations,  § 1 9 

I.  Determination,  of  quantity,  §2 9 

1.  Weighing,  § 3 9 

a.  The  balance 9 

Accuracy,  §4 10 

Sensibility,  §5 11 

Testing,  § 6 and  §7 12 

b.  The  weights,  § 8 14 

c.  The  process  of  weighing,  § 9 15 

Rules,  § 10 17 

2.  Measuring,  § 11 _. 18 

a.  The  measuring  of  gases,  §12 19 

Correct  reading-off,  § 13 20 

Influence  of  temperature,  § 14 21 

Influence  of  pressure,  § 15 21 

Influence  of  moisture,  § 16 22 

b.  The  measuring  of  fluids,  § 17 22 

a.  Measuring  vessels  graduated  to  hold  certain  volumes  of 

fluid. 

aa.  Vessels  serving  to  measure  out  one  definite  volume  of 
fluid. 

1.  Measuring  flasks,  § 18 22 

bb.  Vessels  serving  to  measure  out  different  volumes  of 

fluid. 

2.  The  graduated  cylinder,  § 19 24 

(3.  Measuring  vessels  graduated  to  deliver  certain  volumes 

of  fluid. 

aa.  Vessels  serving  to  measure  out  one  definite  volume 
of  fluid. 

3.  The  graduated  pipette,  § 20 24 

bb.  Vessels  serving  to  measure  out  different  volumes  of 

fluid. 

4.  The  Burette. 

I.  Mohr’s  burette,  § 21 26 

II.  Gay-Lussac’s  burette,  § 22 30 

III.  Geissler’s  burette,  § 23 31 


CONTENTS. 


viii 


PAGE 


II.  Preliminary  operations.  Preparation  of  substances  for  the  processes 
of  quantitative  analysis. 

1.  Selection  of  the  sample,  § 24 81 

2.  Mechanical  division,  § 25 82 

3.  Desiccation,  § 26 34 

Desiccators,  § 27 35 

Water-baths,  § 28 36 

Air-baths,  § 29 38 

Paraffine-baths,  § 30 40 

III.  General  procedure  in  quantitative  analysis,  § 32 40 

1.  Weighing  the  substance,  § 33 41 

2.  Estimation  of  water,  § 34 42 

a.  Estimation  of  water  by  loss  of  weight,  § 35 43 

b.  Estimation  of  water  by  direct  weighing,  § 36 44 

3.  Solution  of  substances,  § 37 46 

a.  Direct  solution,  § 38 47 

b.  Decomposition  by  fluxing,  § 39 48 

4.  Conversion  of  the  dissolved  substance  into  a weighable  form, 

§ 40 48 

a.  Evaporation,  § 41 49 

Weighing  of  residues,  § 42 52 

b.  Precipitation,  § 43 53 

a.  Separation  of  precipitates  by  decantation,  § 44. . 55 

0.  Separation  of  precipitates  by  filtration,  § 45 55 

aa.  Filtering  apparatus 56 

bb.  Rules  to  be  observed  in  the  process  of  filtra- 
tion, § 46 58 

cc .-  Washing  of  precipitates,  § 47 , 59 

y.  Separation  of  precipitates  by  decantation  and  fil- 
tration combined,  § 48 60 

Further  treatment  of  precipitates  preparatory  to 

weighing,  § 49 61 

aa.  Drying  of  precipitates,  § 50 61 

bb.  Ignition  of  precipitates,  § 51 62 

First  method,  § 52 64 

Second  method,  § 53 65 

Bunsen’s  method  of  rapid  filtration,  § 53,  a 66 

Bunsen’s  treatment  of  precipitates,  § 53,  b. 77 

Advantages  of  Bunsen’s  new  method,  § 53,  c 77 

Bunsen’s  simple  exhausting  apparatus,  § 53,  d 79 

5.  Volumetric  analysis,  § 54 80 


SECTION  II. 


Reagents,  § 55 83 

A.  Reagents  for  gravimetric  analysis  in  the  wet  way. 

L Simple  solvents,  § 56 83 

II.  Acids  and  halogens. 

a.  Oxygen  acids,  § 57 84 

b.  Hydrogen  acids  and  halogens,  § 58 84 

c.  Sulpho-acids 85 

III.  Bases  and  metals. 

a.  Oxygen  bases  and  metals. 

a.  Alkalies,  and 

0.  Alkaline  earths,  § 59 86 

y.  Heavy  metals  and  oxides  of  heavy  metals,  § 60. . ..  86 

b.  Sulpho-bases 87 


CONTENTS.  i X 

PAGB 

IY.  Salts. 

a.  Salts  of  tlie  alkalies,  § 61 87 

b.  Salts  of  the  alkaline  earths,  § 62 88 

c.  Salts  of  the  oxides  of  the  heavy  metals,  § 63 89 

B.  Reagents  for  gravimetric  analysis  in  the  dry  way,  § 64 90 

G.  Reagents  for  volumetric  analysis,  § 65 91 

D.  Reagents  for  organic  analysis,  § 66 96 

SECTION  III. 

Forms  and  combinations  in  which  substances  are  separated  from  each  other, 
or  weighed,  § 67 101 

A.  Bases. 

FIRST  GROUP. 

1.  Potassa,  § 68 102 

2.  Soda,  § 69 103 

3.  Ammonia,  § 70 105 

SECOND  GROUP. 

1.  Baryta,  §71 106 

2.  Strontia,  § 72 107 

3.  Lime,  § 73 108 

4.  Magnesia,  § 74 110 

THIRD  GROUP. 

1.  Alumina,  § 75 112 

2.  Sesquioxide  of  chromium,  § 76 114 

FOURTH  GROUP. 

1.  Oxide  of  zinc,  § 77 114 

2.  Protoxide  of  manganese,  § 78 116 

3.  Protoxide  of  nickel,  § 79 118 

4.  Protoxide  of  cobalt,  § 80 119 

5.  Protoxide;  and  6.  Sesquioxide  of  iron,  § 81 121 

FIFTH  GROUP. 

1.  Oxide  of  silver,  § 82 124 

2.  Oxide  of  lead,  § 83 125 

3.  Suboxide  ; and  4.  Oxide  of  mercury,  § 84 127 

5.  Oxide  of  copper,  § 85 129 

6.  Teroxide  of  bismuth,  § 86 131 

7.  Oxide  of  cadmium,  § 87 133 

SIXTH  GROUP. 

1.  Teroxide  of  gold,  § 88 134 

2.  Binoxide  of  platinum,  § 89 134 

3.  Teroxide  of  antimony,  § 90 135 

4.  Peroxide  of  tin;  and  5.  Binoxide  of  tin,  § 91 136 

6.  Arsenious  acid  ; and  7.  Arsenic  acid,  § 92 137 

B.  Acids. 

FIRST  GROUP.  § 93. 

1.  Arsenious  and  arsenic  acids. 

2.  Chromic  acid 139 

3.  Sulphuric  acid 140 


X 


CONTENTS. 


PAGE 

4.  Phosphoric  acid 140 

5.  Boracic  acid 144 

6.  Oxalic  acid 144 

7.  Hydrofluoric  acid 144 

8.  Carbonic  acid 145 

9.  Silicic  acid 145 

SECOND  GROUP.  § 94. 

1.  Hydrochloric  acid 146 

2.  Hydrobromic  acid 146 

3.  Hydriodic  acid 147 

4.  Hydrocyanic  acid 148 

5.  Hydrosulphuric  acid 148 

THIRD  GROUP.  § 95. 

1.  Nitric  acid 148 

2.  Chloric  acid. 148 

SECTION  IV. 

Determination  of  bodies,  § 96 149 

I.  Estimation  of  the  bases. 

FIRST  GROUP. 

1.  Potassa,  § 97 151 

2.  Soda,  § 98 154 

3.  Ammonia,  § 99 156 

Supplement  to  first  group,  § 100. 

4.  Lithia 161 

SECOND  GROUP. 

1.  Baryta,  § 101 164 

2.  Strontia,  § 102 166 

3.  Lime,  § 103 168 

4.  Magnesia,  § 101 171 

THIRD  GROUP. 

1.  Alumina,  § 105 174 

2.  Sesquioxide  of  chromium,  § 106 176 

Supplement  to  third  group,  § 107. 

3.  Titanic  acid 178 

FOURTH  GROUP. 

1.  Oxide  of  zinc,  § 108 179 

2.  Protoxide  of  manganese,  § 109 182 

3.  Protoxide  of  nickel,  § 110 187 

4.  Protoxide  of  cobalt,  § 111 189 

5.  Protoxide  of  iron,  § 112 192 

6.  Sesquioxide  of  iron,  § 113 ... . ’. 199 

Supplement  to  fourth  group,  §.  114. 

7.  Sesquioxide  of  uranium 205 

FIFTH  GROUP. 

1.  Oxide  of  silver,  § 115 205 

;2.  Oxide  of  lead,  § 116 216 

3.  Suboxide  of  mercury,  § 117 220 


CONTENTS. 


XI 


PAGE 

4.  Oxide  of  mercury,  §118 220 

5.  Oxide  of  copper,  §119 225 

6.  Teroxide  of  bismuth,  § 120 232 

7.  Oxide  of  cadmium,  § 121 235 

Supplement  to  fifth  group,  § 122. 

8.  Protoxide  of  palladium 236 

SIXTH  GROUP. 

1.  Teroxide  of  gold,  § 123  237 

2.  Binoxide  of  platinum,  § 124 239 

3.  Teroxide  of  antimony,  § 125 241 

4.  Protoxide  of  tin  ; and  5.  Binoxide  of  tin,  § 126  245 

6.  Arsenious  acid;  and  7.  Arsenic  acid,  § 127 249 

Supplement  to  sixth  group,  § 128. 

8,  Molybdic  acid 255 

II.  Estimation  of  the  acids. 

FIRST  GROUP. 

First  Division. 

1.  Arsenious  and  arsenic  acids,  § 129  256 

2.  Chromic  acid,  § 130 257 

Supplement , § 131. 

1.  Selenious  acid 261 

2.  Sulphurous  acid 262 

3.  Hyposulphurous  acid 263 

4.  Iodic  acid 263 

5.  Nitrous  acid 263 

Second  Division. 

Sulphurous  acid.  § 132  264 

Supplement , § 133. 

Hydro  fluosilicic  acid 269 

Third  Division. 

1.  Phosphoric  acid. 

I.  Determination,  § 134 269 

II.  Separation  from  the  bases,  § 135 275 

2.  Boracic  acid,  § 136  279 

3.  Oxalic  acid,  § 137 282 

4.  Hydrofluoric  acid,  § 138  284 

Fourth  Division. 

1.  Carbonic  acid,  § 139 285 

2.  Silicic  acid,  § 140 299 

SECOND  GROUP. 

1.  Hydrochloric  acid,  § 141 304 

Supplement : free  chlorine,  § 142 307 

2.  Hydrobromic  acid,  § 143 309 

Supplement:  free  bromine,  §144 311 

3.  Hydriodic  acid,  § 145 311 

Supplement:  free  iodine,  § 146 313 

4.  Hydrocyanic  acid,  § 147 316 

5.  Hydrosulphuric  acid,  § 148 321 

THIRD  GROUP. 


1.  Nitric  acid,  § 149  , 

2.  Chloric  acid,  § 150 


328 

335 


Xll 


CONTENTS. 


SECTION  Y. 

PAGB 

Separation  of  bodies,  § 151 337 

I.  SEPARATION  OP  BASES  FROM  EACH  OTHER. 

FIRST  GROUP. 

Separation  of  the  alkalies  from  each  other,  § 152 339 

SECOND  GROUP. 

I.  Separation  of  the  oxides  of  the  second  group  from  those  of  the  first, 

§ 153  343 

II.  Separation  of  the  oxides  of  the  second  group  from  each  other,  § 154 . . 346 

THIRD  GROUP. 

I.  Separation  of  the  oxides  of  the  third  group  from  the  alkalies,  § 155. . 350 

II.  Separation  of  the  oxides  of  the  third  group  from  the  alkaline  earths, 

§ 156  351 

III.  Separation  of  the  oxides  of  the  third  group  from  each  other,  § 157. . . 354 

FOURTH  GROUP. 

I.  Separation  of  the  oxides  of  the  fourth  group  from  the  alkalies, 

§ 158 355 

II.  Separation  of  the  oxides  of  the  fourth  group  from  the  alkaline 

earths,  159  356 

III.  Separation  of  the  oxides  of  the  fourth  group  from  those  of  the  third 

and  from  each  other,  § 160 358 

IV.  Separation  of  sesquioxide  of  iron,  alumina,  protoxide  of  manganese, 

lime,  magnesia,  potassa,  and  soda,  § 161 370 

Separation  of  sesquioxide  of  uranium  from  the  oxides  of  groups  I. — IV.  373 

FIFTH  GROUP. 

I.  Separation  of  the  oxides  of  the  fifth  group  from  those  of  the  preceding 

four  groups,  § 162 375 

II.  Separation  of  the  oxides  of  the  fifth  group  from  each  other,  § 163. . . . 379 

SIXTH  GROUP. 

I.  Separation  of  the  oxides  of  the  sixth  group  from  those  of  the  first  five 

groups,  § 164 387 

II.  Separation  of  the  oxides  of  the  sixth  group  from  each  other.  § 165. . . 397 

II.  SEPARATION  OF  ACIDS  FROM  EACH  OTHER. 

FIRST  GROUP. 

Separation  of  the  acids  of  the  first  group  from  each  other,  § 166 402 

SECOND  GROUP. 

I.  Separation  of  the  acids  of  the  second  group  from  those  of  the  first, 

§ 167 409 

Supplement. — Analysis  of  compounds  containing  sulphides  of  the 

alkali  metals,  carbonates,  sulphates,  and  hyposulphites,  § 168.  . . . 411 

II.  Separation  of  the  acids  of  the  second  group  from  each  other,  § 169. . 412 


CONTENTS.  xiii 

THIRD  GROUP. 

PAGE 

I.  Separation  of  the  acids  of  the  third  group  from  those  of  the  two  first 

groups,  § 170 418 

II.  Separation  of  the  acids  of  the  third  group  from  each  other 419 

SECTION  VI. 

Ultimate  analysis  of  organic  bodies,  §171 420 

I.  Qualitative,  § 172 421 

II.  Quantitative,  § 173 423 

A.  Substances  consisting  of  carbon  and  hydrogen,  or  of  carbon,  hydro- 

gen, and  oxygen. 

a.  Solid  bodies. 

Combustion  with  oxide  of  copper,  § 174 424 

Completion  of  the  combustion  by  oxygen  gas,  § 176 431 

Combustion  with  chromate  of  lead  (and  bichromate  of  potash), 

§ 177 431 

Combustion  with  oxide  of  copper  and  oxygen  gas,  § 178  432 

Volatile  bodies,  or  bodies  undergoing  alteration  at  100°, 

§179 435 

b.  Liquid  bodies. 

a.  Volatile  bodies,  § 180 435 

/?.  Non-volatile  bodies,  § 181 437 

Supplement  to  A.  — Modified  apparatus  for  absorption  of  carbonic 

acid,  § 182  438 

B.  Substances  consisting  of  carbon,  hydrogen,  oxygen,  and  nitrogen. 

a.  Estimation  of  carbon  and  hydrogen,  § 183 439 

b.  Estimation  of  nitrogen. 

a.  From  the  volume,  § 184 440 

/?.  By  conversion  into  ammonia,  after  Varrentrapp  and  Will, 

§185 . . . 442 

C.  Analysis  of  bodies  containing  sulphur,  § 186  445 

D.  Estimation  of  phosphorus  in  organic  bodies,  § 187 448 

E.  Analysis  of  substances  containing  chlorine,  bromine,  or  iodine, 

§ 188 449 

F.  Analysis  of  organic  substances  containing  inorganic  bodies,  § 189. . 451 

III.  Determination  of  the  equivalent  of  organic  bodies. 

1.  From  their  combining  proportions  with  other  bodies,  § 190 452. 

2.  From  their  vapor-density,  §191 453 

3.  From  their  products  of  decomposition,  § 192 457 


DIVISION  II. 


Calculation  of  analyses 458 

I.  Calculation  of  the  constituent  sought  from  the  compound  produced, 

and  exhibition  of  the  results  in  per-cents,  § 193 458 

1.  When  the  substance  sought  has  been  separated  in  the  free  state. 

a.  Solid  bodies,  liquids,  or  gases,  which  have  been  determined 

by  weight,  § 194 458 

b.  G-ases  which  have  been  measured,  § 195  459 

2.  When  the  substance  sought  has  been  separated  in  combination 

with  another,  § 196  462 

3 Calculation  of  indirect  analyses,  § 197  464 

Supplement  to  I. — Remarks  on  loss  and  excess,  and  on  taking  the 

average,  § 198  466 

II.  Deduction  of  empirical  formulae,  § 199 468 

III.  Deduction  of  rational  formulae,  § 200  471 

IV.  Calculation  of  the  density  of  vapors,  § 201  475 


XIV 


CONTENTS. 


PART  II. 

SPECIAL  PART. 

PAGE 

1.  Analysis  of  fresh  water,  § 202  483 

2.  Acidimetry. 

A.  Estimation  by  specific  gravity,  § 203 487 

B.  Determination  of  the  acid  by  saturation  with  an  alkaline  fluid  of 

known  strength,  § 204 487 

Kiefer’s  modification  of  the  process,  § 205 496 

3.  Alkalimetry. 

A.  Estimation  of  potassa,  soda,  or  ammonia,  from  the  density  of  their 

solutions,  § 206 498 

B.  Estimation  of  the  amount  of  caustic  and  carbonated  alkali  in  com- 

mercial alkalies 498 

Method  of  Descroizilles  and  Gay-Lussac,  § 207 499 

Modification  by  Mohr,  § 208 500 

C.  Estimation  of  caustic  alkali  in  the  presence  of  carbonates,  § 209.  . 502 

D.  Estimation  of  carbonate  of  soda  in  presence  of  carbonate  of 

potassa  502 

4.  Estimation  of  alkaline  earths  by  the  alkalimetric  method,  § 210 503 

5.  Chlorimetry,  § 211 504 

Preparation  of  the  solution  of  chloride  of  lime 504 

A.  Penot’s  method,  §212 505 

B.  Otto’s  method,  § 213 506 

Modification 507 

C.  Bunsen’s  method 508 

6.  Valuation  of  manganese,  § 214 508 

I.  Drying-  the  sample 508 

II.  Estimation  of  the  binoxide  of  mang-anese,  § 215 509 

A.  Fresenius  and  Will’s  method 509 

B.  Bunsen’s  method 512 

C.  Method  by  means  of  iion 512 

III.  Estimation  of  moisture  in  mang-anese,  § 216 513 

IV.  Estimation  of  the  amount  of  hydrochloric  acid  required  for  the 

complete  decomposition  of  a manganese,  § 217 513 

7.  Analysis  of  common  salt,  §218 514 

8.  Analysis  of  gunpowder,  § 219 514 

9.  Analysis  of  native  silicates,  § 220 516 

10.  Analysis  of  limestones,  dolomites,  marls,  &c 518 

A.  Method  of  complete  analysis,  § 221 519 

B.  Volumetric  determination  of  carbonate  of  lime,  § 222  523 

11.  Analysis  of  Iron  ores,  § 223 524 

A.  Estimation  of  iron 524 

B.  Estimation  of  iron,  manganese,  silica,  and  phosphoric  acid 524 

C.  Estimation  of  sulphur 525 

D.  Estimation  of  titanium 525 

12.  Assay  of  copper  ores.  § 224 525 

A.  Mohr’s  method  for  oxides,  &c 525 

B.  Gibbs’  method  for  sulphides 526 

C.  Storerand  Pearson’s  method  for  sulphides 526 

13.  Analysis  of  galena,  § 225 527 

14.  Silver  assay,  § 226 528 

A.  Assay  of  poor  ores 528 

B.  Assay  of  rich  ores 531 

C.  Bullion  assay 531 

15.  Gold  assay,  § 227 531 

A.  Ores  of  the  first  class 531 

B.  Ores  of  the  second  class  (sulphides) 552 

16.  Assay  of  zinc  ores,  § 228 . 534 


CONTENTS. 


yv 

PAGE 

17.  Analysis  of  iron  and  steel,  § 229  535 

18.  Analysis  of  manures,  § 231 543 

A.  General  process,  § 232 543 

B.  Analysis  of  guano,  § 233 545 

C.  Analysis  of  bone  dust,  § 234 547 

D.  Analysis  of  superphosphate  of  lime,  § 235 548 

Abridged  analysis  of  superphosphates,  § 236 550 

E.  Analysis  of  bone  black,  § 237 551 

Estimation  of  the  carbonate  of  lime,  § 238 551 

19.  Analysis  of  coal  and  peat,  § 239 552 

20.  Analysis  of  atmospheric  air,  § 240 553 

A.  Determination  of  the  water  and  carbonic  acid,  § 241 553 

B.  Determination  of  the  nitrogen  and  oxygen,  § 242 558 


PART  III. 

Exercises  for  practice 564 


APPENDIX. 

Analytical  experiments 581 

Tables  for  the  calculation  of  analyses 603 — 620 

I.  Equivalents  of  the  elements 603 

II.  Composition  of  bases  and  oxygen  acids 604 

III.  Beduction  of  compounds  found  to  constituents  sought  by  simple 

multiplication  or  division 608 

IY.  Amount  of  constituent  sought  for  each  number  of  compound 

found 610 

Y.  Specific  gravity  and  absolute  weight  of  several  gases  620 

VI.  Comparison  of  degrees  of  mercurial  thermometer  with  those  of 

air  thermometer 620 


EDITOR’S  APPENDIX. 

Dr.  Gibbs’  method  of  correcting  volume  of  gases 621 

Assay  of  chromic  iron 621 

Separation  of  phosphoric  acid  from  lime,  alumina,  and  iron 022 


INTRODUCTION 


As  we  have  already  seen  in  the  " Manual  of  Qualitative  Analysis,” — 
to  which  the  present  work  may  be  regarded  as  the  sequel, — Chemical 
Analysis  comprises  two  branches,  viz. : qualitative  analysis  and  quanti- 
tative analysis , the  object  of  the  former  being  to  ascertain  the  nature , 
that  of  the  latter  to  determine  the  amount , of  the  several  component 
parts  of  any  compound. 

By  qualitative  analysis  we  convert  the  unknown  constituents  of  a 
body  into  certain  known  forms  or  combinations ; and  we  are  thus  en- 
abled to  draw  correct  inferences  respecting  the  nature  of  these  unknown 
constituents.  Quantitative  analysis  attains  its  object,  according  to  cir- 
cumstances, often  by  very  different  ways ; the  two  methods  most  widely 
differing  from  each  other,  are  analysis  by  weight , or  gravimetric  analysis , 
and  analysis  by  measure , or  volumetric  analysis. 

Gravimetric  analysis  has  for  its  object  to  convert  the  known  con- 
stituents of  a substance  into  forms  or  combinations  which  will  admit  of 
the  most  exact  determination  of  their  weight,  and  of  which,  moreover,  the 
composition  is  accurately  known.  These  new  forms  or  combinations  may 
be  either  educts  from  the  analyzed  substance,  or  they  may  be  'products. 
In  the  former  case  the  ascertained  weight  of  the  eliminated  substance  is 
the  direct  expression  of  the  amount  in  which  it  existed  in  the  compound 
under  examination ; whilst  in  the  latter  case,  that  is,  when  we  have  to 
deal  with  products , the  quantity  in  which  the  eliminated  constituent  was 
originally  present  in  the  analyzed  compound,  has  to  be  deduced  by 
calculation  from  the  quantity  in  which  it  exists  in  its  new  combination. 

The  following  example  will  serve  to  illustrate  these  points : — Suppose 
we  wish  to  determine  the  quantity  of  mercury  contained  in  the  chloride 
of  that  metal ; now,  we  may  do  this,  either  by  precipitating  the  metallic 
mercury  from  the  solution  of  the  chloride,  say  by  means  of  protochloride 
of  tin;  or  we  may  attain  our  object  by  precipitating  the  solution  by  sul- 
phuretted hydrogen,  and  weighing  the  precipitated  sulphide  of  mercury. 
100  parts  of  chloride  of  mercury  consist  of  73*82  of  mercury  and  26*18 
of  chlorine;  consequently,  if  the  process  is  conducted  with  absolute 
accuracy,  the  precipitation  of  100  parts  of  chloride  of  mercury  by  proto- 
chloride of  tin  will  yield  73*82  parts  of  metallic  mercury.  With  equally 
exact  manipulation  the  other  method  yields  85*634  parts  of  sulphide  of 
mercury. 

Now,  in  the  former  case  we  find  the  number  73*82  directly ; in  the 
latter  case  we  have  to  deduce  it  by  calculation : — (100  parts  of  sulphide  of 


2 


INTRODUCTION. 


mercury  contain  86*207  parts  of  mercury  ; how  much  mercury  do  85*634 
parts  contain  ?) 

100  : 85*634  : : 86*207  : a>— »=73*82. 

As  already  hinted,  it  is  absolutely  indispensable  that  the  forms  into 
which  bodies  are  converted  for  the  purpose  of  estimation  by  weight  should 
fulfil  two  conditions : first,  they  must  be  capable  of  being  weighed  exactly ; 
secondly,  they  must  be  of  known  composition, — for  it  is  quite  obvious,  on 
the  one  hand,  that  accurate  quantitative  analysis  must  be  altogether  im- 
possible if  the  substance  the  quantity  of  which  it  is  intended  to  ascertain, 
does  not  admit  of  correct  weighing ; and  on  the  other  hand,  it  is  equally 
evident  that  if  we  do  not  know  the  exact  composition  of  a new  product, 
we  lack  the  necessary  basis  of  our  calculation. 

Volumetric  analysis  is  based  upon  a very  different  principle  from  that 
of  gravimetric  analysis ; viz.,  it  affects  the  quantitative  determination  of 
a body,  by  converting  it  from  a certain  definite  state  to  another  equally 
definite  state,  by  means  of  a fluid  of  accurately  known  power  of  action, 
and  under  circumstances  which  permit  the  analyst  to  mark  with  rigorous 
precision  the  exact  point  when  the  conversion  is  accomplished.  The  fol- 
lowing example  will  serve  to  illustrate  the  principle  of  this  method  : — 
Permanganate  of  potassa  added  to  a solution  of  sulphate  of  protoxide  of 
iron,  acidified  with  sulphuric  acid,  immediately  converts  the  protoxide  of 
iron  to  sesquioxide  ; the  permanganic  acid,  which  is  characterized  by  its 
intense  colour,  yielding  up  oxygen  and  changing  to  protoxide  of  manga- 
nese, which  combines  with  the  sulphuric  acid  present,  to  colorless  sulphate 
of  protoxide  of  manganese.  If,  therefore,  to  an  acidified  fluid  containing 
protoxide  of  iron,  we  add,  drop  by  drop,  a solution  of  permanganate  of 
potassa,  its  red  color  continues  for  some  time  to  disappear  upon  stirring ; 
but  at  last  a point  is  reached  when  the  coloration  imparted  to  the  fluid 
by  the  last  drop  added  remains  : this  point  marks  the  termination  of  the 
conversion  of  the  protoxide  of  iron  to  sesquioxide. 

Now,  by  accurately  determining  the  strength  or  power  of  action  of  the 
solution  of  permanganate  of  potassa — which  is  done  simply  by  making  it 
act  upon  a known  quantity  of  protoxide  of  iron  in  solution,  and  correctly 
noting  how  much  of  it  is  required  to  effect  the  conversion  of  that  pro- 
toxide to  the  state  of  sesquioxide — we  are  now  able  with  this  solution  to 
determine  the  exact  amount  of  protoxide  of  iron  present  in  any  solution. 
Thus,  we  will  assume,  for  instance,  that  we  have  found  it  takes  exactly 
100  parts  of  our  solution  of  permanganate  of  potassa  to  oxidize  2 parts  of 
protoxide  of  iron  ; if  now,  in  testing,  with  this  standard  solution  of  per- 
manganate of  potassa,  any  solution  containing  an  unknown  quantity  of 
protoxide  of  iron,  we  find  that  100  parts  of  our  standard  fluid  are  required 
to  oxidize  the  iron,  we  know  at  once  that  the  examined  fluid  contained 
exactly  2 parts  of  protoxide  of  iron ; if  50  parts  are  required,  we  know 
that  1 part  of  protoxide  of  iron  was  present,  &c.  &c.  Accordingly,  by 
simply  measuring  the  quantity  used  of  our  standard  solution  of  perman- 
ganate of  potassa,  we  arrive  at  once  at  an  accurate  knowledge  of  the  amount 
of  protoxide  of  iron. 

As  the  process  of  measuring  is  mostly  adopted,  in  preference  to  that 
of  weighing,  for  determining  the  quantity  used  of  the  standard  fluid,  we 
give  to  this  analytical  method  the  name  of  “ analysis  by  measure.”  It 
generally  leads  to  the  attainment  of  the  object  in  view  with  much  greater 
expedition  than  is  the  case  with  analysis  by  weight. 


INTRODUCTION. 


3 


To  this  brief  intimation  of  the  general  purport  and  object  of  quantita- 
tive analysis,  and  the  general  mode  of  proceeding  in  analytical  re- 
searches, I have  to  add  that  certain  qualifications  are  essential  to  those 
who  would  devote  themselves  successfully  to  the  pursuit  of  this  branch. 
These  qualifications  are,  1,  theoretical  knowledge  ; 2,  skill  in  manipula- 
tion ; and  3,  strict  conscientiousness. 

The  preliminary  knowledge  required  consists  in  an  acquaintance  with 
qualitative  analysis,  the  stoichiometric  laws,  and  simple  arithmetic.  Thus 
prepared,  we  shall  understand  the  method  by  which  bodies  are  separated 
and  determined,  and  we  shall  be  in  a position  to  perform  our  calcu- 
lations, by  which,  on  the  one  hand,  the  formulae  of  compounds  are 
deduced  from  the  analytical  results,  and,  on  the  other  hand,  the  correct- 
ness of  the  adopted  methods  is  tested,  and  the  results  obtained  are  con- 
trolled. To  this  knowledge  must  be  joined  the  ability  of  performing  the 
necessary  practical  operations.  This  axiom  generally  holds  good  for  all 
applied  sciences,  but  if  it  is  true  of  one  more  than  another,  quantitative 
analysis  is  that  one.  The  most  extensive  and  solid  theoretical  acquire- 
ments will  not  enable  us,  for  instance,  to  determine  the  amount  of  com- 
mon salt  present  in  a solution,  if  we  are  without  the  requisite  dexterity 
to  transfer  a fluid  from  one  vessel  to  another  without  the  smallest  loss 
by  spirting,  running  down  the  side,  &c.  The  various  operations  of 
quantitative  analysis  demand  great  aptitude  and  manual  skill,  which  can 
be  acquired  only  by  practice.  But  even  the  possession  of  the  greatest 
practical  skill  in  manipulation,  joined  to  a thorough  theoretical  know- 
ledge, will  still  prove  insufficent  to  insure  a successful  pursuit  of  quanti- 
tative researches,  unless  also  combined  with  a sincere  love  of  truth , and 
a firm  determination  to  accept  none  but  thoroughly  confirmed  results. 

Every  one  who  has  been  engaged  in  quantitative  analysis  knows  that 
cases  will  sometimes  occur,  especially  when  commencing  the  study,  in 
which  doubts  may  be  entertained  as  to  whether  the  result  will  turn  out 
correct,  or  in  which  even  the  operator  is  positively  convinced  that  it 
cannot  be  quite  correct.  Thus,  for  instance,  a small  portion  of  the  sub- 
stance under  investigation  may  be  spilled  ; or  some  of  it  lost  by  decrepi- 
tation ; or  the  analyst  may  have  reason  to  doubt  the  accuracy  of  his 
weighing ; or  it  may  happen  that  two  analyses  of  the  same  substance  do 
not  exactly  agree.  In  all  such  cases  it  is  indispensable  that  the  operator 
should  be  conscientious  enough  to  repeat  the  whole  process  over  again. 
He  who  is  not  possessed  of  this  self-command — who  shirks  trouble  where 
truth  is  at  stake — who  would  be  satisfied  with  mere  assumptions  and 
guesswork,  where  the  attainment  of  positive  certainty  is  the  object, 
must  be  pronounced  just  as  deficient  in  the  necessary  qualifications  for 
quantitative  analytical  researches  as  he  who  is  wanting  in  knowledge  or 
skill.  He,  therefore,  who  cannot  fully  trust  his  work — who  cannot  swear 
to  the  correctness  of  his  results,  may  indeed  occupy  himself  with  quanti- 
tative analysis  by  way  of  practice,  but  he  ought  on  no  account  to  publish 
or  use  his  results  as  if  they  were  positive,  since  such  proceeding  could 
not  conduce  to  his  own  advantage,  and  would  certainly  be  mischievous 
as  regards  the  science. 

The  domain  of  quantitative  analysis  may  be  said  to-  extend  over  all 
matter — that  is,  in  other  words,  anything  corporeal  may  become  the 
object  of  quantitative  investigation.  The  present  work,  however,  is  in- 
tended to  embrace  only  the  substances  used  in  pharmacy,  arts,  trades,  and 
agriculture. 


4 


INTRODUCTION. 


Quantitative  analysis  may  be  subdivided  into  two  branches,  viz.,  ana- 
lysis of  mixtures , and  analysis  of  chemical  compounds.  This  division  may 
appear  at  first  sight  of  very  small  moment,  yet  it  is  necessary  that  we 
should  establish  and  maintain  it,  if  we  would  form  a clear  conception  of 
the  value  and  utility  of  quantitative  research.  The  quantitative  analy- 
sis of  mixtures,  too,  has  not  the  same  aim  as  that  of  chemical  com- 
pounds ; and  the  method  applied  to  secure  the  correctness  of  the  results 
in  the  former  case  is  different  from  that  adopted  in  the  latter.  The 
quantitative  analysis  of  chemical  compounds  also  rather  subserves  the 
purposes  of  the  science,  whilst  that  of  mixtures  belongs  to  the  practical 
purposes  of  life.  If,  for  instance,  I analyze  the  salt  of  an  acid,  the  result 
of  the  analysis  will  give  me  the  constitution  of  that  acid,  its  combining 
proportion,  saturating  capacity,  &c. ; or,  in  other  words,  the  results  ob- 
tained will  enable  me  to  answer  a series  of  questions  of  which  the  solu- 
tion is  important  for  the  theory  of  chemical  science  : but  if,  on  the  other 
band,  I analyze  gunpowder,  alloys,  medicinal  mixtures,  ashes  of  plants, 
&c.,  &c.,  I have  a very  different  object  in  view ; I do  not  want  in  such 
cases  to  apply  the  results  which  I may  obtain  to  the  solution  of  any  the- 
oretical question  in  chemistry,  but  I want  to  render  a practical  service 
either  to  the  arts  and  industries,  or  to  some  other  science.  If  in  the 
analysis  of  a chemical  compound  I wish  to  control  the  results  obtained, 
I may  do  this  in  most  cases  by  means  of  calculations  based  on  stoichio- 
metric data,  but  in  the  case  of  a mixture  a second  analysis  is  necessary 
to  confirm  the  correctness  of  the  results  afforded  by  the  first. 

The  preceding  remarks  clearly  show  the  immense  importance  of  quan- 
titative analysis.  It  may,  indeed,  be  averred  that  chemistry  owes  to 
this  branch  its  elevation  to  the  rank  of  a science,  since  quantitative 
researches  have  led  us  to  discover  and  determine  the  laws  which  govern 
the  combinations  and  transpositions  of  the  elements.  Stoichiometry  is 
entirely  based  upon  the  results  of  quantitative  investigations  ; all  rational 
views  respecting  the  constitution  of  compounds  rest  upon  them  as  the 
only  safe  and  solid  basis. 

Quantitative  analysis,  therefore,  forms  the  strongest  and  most  powerful 
lever  for  chemistry  as  a science,  and  not  less  so  for  chemistry  in  its 
applications  to  the  practical  purposes  of  life,  to  trades,  arts,  manufac- 
tures, and  likewise  in  its  application  to  other  sciences.  It  teaches  the 
mineralogist  the  true  nature  of  minerals,  and  suggests  to  him  principles 
and  rules  for  their  recognition  and  classification.  It  is  an  indispen- 
sable auxiliary  to  the  physiologist ; and  agriculture  has  already  derived 
much  benefit  from  it ; but  far  greater  benefits  may  be  predicted.  We 
need  not  expatiate  here  upon  the  advantages  which  medicine,  pharmacy, 
and  every  branch  of  industry  derive,  either  directly  or  indirectly,  from 
the  practical  application  of  its  results.  On  the  other  hand,  the  benefit 
thus  bestowed  by  quantitative  analysis  upon  the  various  sciences,  arts, 
&c.,  has  been  in  a measure  reciprocated  by  some  of  them.  Thus  whilst 
stoichiometry  owes  its  establishment  to  quantitative  analysis,  the  stoichio- 
metric laws  afford  us  the  means  of  controlling  the  results  of  our  analyses  so 
accurately  as  to  justify  the  reliance  which  we  now  generally  place  on  them. 
Again,  whilst  quantitative  analysis  has  advanced  the  progress  of  arts  and 
industry,  our  manufacturers  in  return  supply  us  with  the  most  perfect 
platinum,  glass,  and  porcelain  vessels,  and  with  articles  of  india-rubbber, 
without  which  it  would  be  next  to  impossible  to  conduct  our  analytical 
operations  with  the  minuteness  and  accuracy  which  we  have  now  attained. 


INTRODUCTION. 


5 


Although  the  aid  which  quantitative  analysis  thus  derives  from  stoi- 
chiometry, and  the  arts  and  manufactures,  greatly  facilitates  its  practice, 
and  although  many  determinations  are  considerably  abbrieviated  by  volu- 
metric analysis,  it  must  be  admitted,  notwithstanding,  that  the  pursuit 
of  this  branch  of  chemistry  requires  considerable  expenditure  of  time. 
This  remark  applies  especially  to  those  who  are  commencing  the  study, 
for  they  must  not  allow  their  attention  to  be  divided  upon  many  things 
at  one  time,  otherwise  the  accuracy  of  their  results  will  be  more  or  less 
injured.  I would  therefore  advise  every  one  desirous  of  becoming  an 
analytical  chemist  to  arm  himself  with  a considerable  share  of  patience, 
reminding  him  that  it  is  not  at  one  bound,  but  gradually,  and  step  by 
step,  that  the  student  may  hope  to  attain  the  necessary  certainty  in  his 
work,  the  indispensable  self-reliance  which  can  alone  be  founded  on  one’s 
own  results.  However  mechanical,  protracted,  and  tedious  the  opera- 
tions of  quantitative  analysis  may  appear  to  be,  the  attainment  of 
accuracy  will  amply  compensate  for  the  time  and  labor  bestowed  upon 
them;  whilst,  on  the  other  hand,  nothing  can  be  more  disagreeable  than 
to  find,  after  a long  and  laborious  process,  that  our  results  are  incorrect 
or  uncertain.  Let  him,  therefore,  who  would  render  the  study  of  quan- 
titative analysis  agreeable  to  himself,  from  the  very  outset  endeavor,  by 
strict,  nay,  scrupulous  adherence  to  the  conditions  laid  down,  to  attain 
correct  results,  at  any  sacrifice  of  time.  I scarcely  know  a better  and 
more  immediate  reward  of  labor  than  that  which  springs  from  the  at- 
tainment of  accurate  results  and  perfectly  corresponding  analyses.  The 
satisfaction  enjoyed  at  the  success  of  our  efforts  is  surely  in  itself  a 
sufficient  motive  for  the  necessary  expenditure  of  time  and  labor,  even 
without  looking  to  the  practical  benefits  which  we  may  derive  from  our 
operations. 

The  following  are  the  substances  treated  of  in  this  work  : — 


I.  Metalloids,  or  Non-Metallic  Elements. 

Oxygen , Hydrogen , Sulphur , [Selenium,]  Phosphorus , Chlorine , 
Iodine,  Bromine , Fluorine , Nitrogen , Boron , Silicon , Carbon. 

II.  Metals. 

Potassium , Sodium , [Lithium, \ Barium , Strontium , Calcium , 
Magnesium , Aluminium , Chromium , [ Titanium  Zinc , Manganese , 

Nickel , Cobalt , Iron , [ Uranium ,]  Silver , Mercury , Lead , Copper,  Bis- 
muth, Cadmium,  [ Palladium ,]  Cold,  Platinum,  Tin,  Antimony, 
Arsenic,  [ Molybdenum ]. 

(The  elements  enclosed  within  brackets  are  considered  in  supplement- 
ary paragraphs,  and  more  briefly  than  the  rest.) 


I have  divided  my  subject  into  three  parts.  In  the  first,  I treat  of 
quantitative  analysis  generally;  describing,  1st,  the  execution  of  analy- 
sis ; and,  2d,  the  calculation  of  the  results  obtained.  In  the  second,  I 
give  a detailed  description  of  several  special  analytical  processes.  And 
in  the  third,  a number  of  carefully  selected  examples,  which  may  serve 
as  exercises  for  the  groundwork  of  the  study  of  quantitative  analysis. 


6 


INTRODUCTION. 


The  following  table  will  afford  the  reader  a clear  and  definite  notion 
of  the  contents  of  the  whole  work  : — 

I.  GENERAL  PART. 

A — Execution  of  Analysis. 

1.  Operations. 

2.  Reagents. 

3.  Eorms  and  combinations  in  which  bodies  are  separated  from  others, 
or  in  which  their  weight  is  determined. 

4.  Determination  of  bodies  in  simple  compounds. 

5.  Separation  of  bodies. 

6.  Organic  elementary  analysis. 

B — Calculation  of  the  Results. 

II.  SPECIAL  PART. 

1.  Analysis  of  waters. 

2.  Analysis  of  such  minerals  and  technical  products  as  are  most  fre- 
quently brought  under  the  notice  of  the  chemist ; including  methods  for 
ascertaining  their  commercial  value. 

3.  Analysis  of  atmospheric  air. 

III.  EXERCISES  FOR  PRACTICE. 

APPENDIX. 

1.  Analytical  experiments. 

2.  Tables  for  the  calculation  of  analytical  results. 


PART  I. 


GENERAL  PART. 


DIVISION  L 


THE  EXECUTION  OF  ANALYSIS. 


SECTION  I. 
OPERATIONS. 


§ !• 

Most  of  the  operations  performed  in  quantitative  research  are  the  same 
as  in  qualitative  analysis,  and  have  been  accordingly  described  in  my 
work  on  that  branch  of  analytical  science.  With  respect  to  such  opera- 
tions I shall,  \ herefore,  confine  myself  here  to  pointing  out  any  modifica- 
tions they  may  require  to  adapt  them  for  application  in  the  quantitative 
branch;  but  I shall,  of  course,  give  a full  description  of  such  as  are 
resorted  to  exclusively  in  quantitative  investigations.  Operations  form- 
ing merely  part  of  certain  specific  processes  will  be  found  described  in 
the  proper  place,  under  the  head  of  such  processes. 

I.  Determination  of  Quantity. 

§ 2. 

The  quantity  of  solids  is  usually  determined  by  weight  / the  quantity 
of  gases  and  fluids,  in  many  cases  by  measure  • upon  the  care  and  accu- 
racy with  which  these  operations  are  performed,  depends  the  value  of  all 
our  results ; I shall  therefore  dwell  minutely  upon  them. 


§ 3. 

1.  Weighing. 

To  enable  us  to  determine  with  precision  the  correct  weight  of  a 
substance,  it  is  indispensable  that  we  should  possess,  1st,  a good  balance, 
and  2d,  accurate  weights. 

a.  The  Balance. 

Fig.  1 represents  a form  of  balance  well  adapted  for  analytical  pur- 
poses. There  are  several  points  respecting  the  construction  and  proper- 
ties of  a good  balance,  which  it  is  absolutely  necessary  for  every  chemist 
to  understand.  The  usefulness  of  this  instrument  depends  upon  two 
points : 1st,  its  accuracy , and  2d,  its  sensibility  or  delicacy . 


10 


OPERATIONS. 


18  *• 


§ 4* 

The  accuracy  of  a balance  depends  upon  the  following  conditions : — 
a.  The  fulcrum  or  the  point  on  which  the  beam  rests  must  lie  above  the 
centre  of  gravity  of  the  balance. 


This  is  in  fact  a condition  essential  to  every  balance.  If  the  fulcrum 
were  placed  in  the  centre  of  gravity  of  the  balance,  the  beam  would  not 
oscillate,  but  remain  in  any  position  in  which  it  is  placed,  assuming  the 
scales  to  be  equally  loaded.  If  the  fulcrum  be  placed  below  the  centre 
of  gravity,  the  balance  will  be  overset  by  the  slightest  impulse. 

When  the  fulcrum  is  above  the  centre  of  gravity  the  balance  represents 
a pendulum,  the  length  of  which  is  equal  to  that  of  the  line  uniting  the 
fulcrum  with  the  centre  of  gravity,  and  this  line  forms  right  angles  with 
the  beam,  in  whatever  position  the  latter  may  be  placed.  Now  if  we 
impart  an  impetus  to  a ball  suspended  by  a thread,  the  ball,  after  having 
terminated  its  vibrations,  will  invariably  rest  in  its  original  perpendicular 
position  under  the  point  of  suspension.  It  is  the  same  with  a properly 
adjusted  balance — impart  an  impetus  to  it,  and  it  will  oscillate  for  some 
time,  but  it  will  invariably  return  to  its  original  position ; in  other 
words,  its  centre  of  gravity  will  finally  fall  back  into  its  perpendicular 
position  under  the  fulcrum,  and  the  beam  must  consequently  reassume 
the  horizontal  position. 

But  to  judge  correctly  of  the  force  with  which  this  is  accomplished,  it 
must  be  borne  in  mind  that  a balance  is  not  a simple  pendulum,  but  a 
compound  one,  i.  e.,  a pendulum  in  which  not  one,  but  many  material 
points  move  round  the  turning  point.  The  inert  mass  to  be  moved  is 
accordingly  equal  to  the  sum  of  these  points,  and  the  moving  force  is 
equal  to  the  excess  of  the  material  points  below,  over  those  above  the 
fulcrum. 

/3.  The  points  of  suspension  of  the  scales  must  be  on  an  exact  level  with 
the  fulcrum.  If  the  fulcrum  be  placed  below  the  line  joining  the  points 
of  suspension,  increased  loading  of  the  scales  will  continually  tend  to 
raise  the  centre  of  gravity  of  the  whole  system,  so  as  to  bring  it  nearer 
and  nearer  the  fulcrum ; the  weight  which  presses  upon  the  scales  com- 
bining in  the  relatively  high-placed  points  of  suspension ; at  last,  when 
the  scales  have  been  loaded  to  a certain  degree,  the  centre  of  gravity 


WEIGHING. 


11 


§5-] 

will  shift  altogether  to  the  fulcrum,  and  the  balance  will  consequently 
cease  to  vibrate — any  further  addition  of  weight  will  finally  overset  the 
beam  by  placing  the  centre  of  gravity  above  the  fulcrum.  If,  on  the 
other  hand,  the  fulcrum  be  placed  above  the  line  joining  the  points  of 
suspension,  the  centre  of  gravity  will  become  more  and  more  depressed 
in  proportion  as  the  loading  of  the  scales  is  increased ; the  line  of  the 
pendulum  will  consequently  be  lengthened,  and  a greater  force  will  be 
required  to  produce  an  equal  turn ; in  other  words,  the  balance  will 
grow  less  sensitive  the  greater  the  load.  But  when  the  three  edges  are 
in  one  plane,  increased  loading  of  the  scales  will,  indeed,  continually 
tend  to  raise  the  centre  of  gravity  towards  the  fulcrum,  but  the  former 
can  in  this  case  never  entirely  reach  the  latter,  and  consequently  the 
balance  will  never  altogether  cease  to  vibrate  upon  the  further  addition 
of  weight,  nor  will  its  sensibility  be  lessened  ; on  the  contrary — speak- 
ing theoretically — a greater  degree  of  sensibility  is  imparted  to  it.  This 
increase  of  sensibility  is,  however,  compensated  for  by  other  circum- 
stances. ( See  § 5.) 

y.  The  beam  must  be  sufficiently  rigid  to  bear  without  bending  the 
greatest  weight  that  the  construction  of  the  balance  admits  of  y since  the 
bending  of  the  beam  would  of  course  depress  the  points  of  suspension  so 
as  to  place  them  below  the  fulcrum,  and  this  would,  as  we  have  just 
seen,  tend  to  diminish  the  sensibility  of  the  balance  in  proportion  to  the 
increase  of  the  load.  It  is,  therefore,  necessary  to  avoid  this  fault  by  a 
proper  construction  of  the  beam.  The  form  best  adapted  for  beams  is 
that  of  an  isosceles  obtuse-angled  triangle,  or  of  a rhombus.  • 

8.  The  arms  of  the  balance  must  be  of  equal  length , i.  e.,  the  points  of 
suspension  must  be  equidistant  from  the  fulcrum , for  if  the  arms  are  of 
unequal  length  the  balance  will  not  be  in  equilibrium,  supposing  the 
scales  to  be  loaded  with  equal  weights,  but  there  will  be  preponderance 
on  the  side  of  the  longer  arm. 

§ 5- 

The  sensibility  of  a balance  depends  principally  upon  the  three  fol- 
lowing conditions  : — 

a.  Tice  friction  of  the  edges  upon  their  supports  must  be  as  slight  as 
possible.  The  greater  or  less  friction  of  the  edges  upon  their  supports 
depends  upon  both  the  form  and  material  of  those  parts  of  the  balance. 
The  edges  must  be  made  of  good  steel,  the  supports  may  be  made  of  the 
same  material ; it  is  better,  however,  that  the  centre  edge  at  least  should 
rest  upon  an  agate  plane.  To  form  a clear  conception  of  how  necessary 
it  is  that  even  the  end  edges  should  have  as  little  friction  as  possible, 
we  need  simply  reflect  upon  what  would  happen  were  we  to  fix  the  scales 
immovably  to  the  beam  by  means  of  rigid  rods.  Such  a contrivance 
would  at  once  altogether  annihilate  the  sensibility  of  a balance,  for  if  a 
weight  were  placed  upon  one  scale,  this  certainly  would  have  a tendency 
to  sink ; but  at  the  same  time  the  connecting  rods  being  compelled  to  form 
constantly  a right  angle  with  the  beam,  the  weighted  scale  would  incline 
inwards,  whilst  the  other  scale  would  turn  outwards,  and  thus  the  arms 
would  become  unequal,  the  shorter  arm  being  on  the  side  of  the  weighted 
scale,  whereby  the  tendency  of  the  latter  to  sink  would  be  immediately 
compensated  for.  The  more  considerable  the  friction  becomes  at  the 
end  edges  of  a balance,  the  more  the  latter  approaches  the  state  just 
now  described,  and  consequently  the  more  is  its  sensibility  impaired. 


12 


OPERATIONS. 


(3.  The  centre  of  gravity  must  be  as  near  as  possible  to  the  fulcrum. 
The  nearer  the  centre  of  gravity  approaches  the  fulcrum,  the  shorter 
becomes  the  pendulum.  If  we  take  two  balls,  the  one  suspended  by  a 
short  and  the  other  by  a long  thread,  and  impart  the  same  impetus  to 
both,  the  former  will  naturally  swing  at  a far  greater  angle  from  its  per- 
pendicular position  than  the  latter.  The  same  must  of  course  happen 
with  a balance  ; the  same  weight  will  cause  the  scale  upon  which  it  is 
placed  to  turn  the  more  rapidly  and  completely,  the  shorter  the  distance 
between  the  centre  of  gravity  and  the  fulcrum.  We  have  seen  above, 
that  in  a balance  where  the  three  edges  are  on  a level  with  each  other, 
increased  loading  of  the  scales  will  continually  tend  to  raise  the  centre 
of  gravity  towards  the  fulcrum.  A good  balance  will  therefore  become 
more  delicate  in  proportion  to  the  increase  of  weights  placed  upon  its 
scales ; but,  on  the  other  hand,  its  sensibility  will  be  diminished  in  about 
the  same  proportion  by  the  increment  of  the  mass  to  be  moved,  anti  by 
the  increased  friction  attendant  upon  the  increase  of  load ; in  other 
words,  the  delicacy  of  a good  balance  will  remain  the  same,  whatever 
may  be  the  load  placed  upon  it.  The  nearer  the  centre  of  gravity  lies 
to  the  fulcrum,  the  slower  are  the  oscillations  of  the  balance.  Hence 
in  regulating  the  position  of  the  centre  of  gravity  we  must  not  go  too 
far,  for  if  it  approaches  the  fulcrum  too  nearly,  the  operation  of  weigh- 
ing will  take  too  much  time. 

y.  The  beam  must  be  as  light  as  possible.  The  remarks  which  we  have 
just  now  made  will  likewise  show  how  far  the  weight  of  the  beam  may 
influence  the  sensibility  of  a balance.  We  have  seen  that  if  a balance 
is  not  actually  to  become  less  delicate  on  increased  loading,  it  must  on 
the  one  hand  have  a tendency  to  become  more  delicate  by  the  continual 
approach  of  the  centre  of  gravity  to  the  fulcrum.  Now  it  is  evident, 
that  the  more  considerable  the  weight  of  the  beam  is,  the  less  will  an 
equal  load  placed  upon  both  scales  alter  the  centre  of  gravity  of  the 
whole  system,  the  more  slowly  will  the  centre  of  gravity  approach  the 
fulcrum,  the  less  will  the  increased  friction  be  neutralized,  and  conse- 
quently the  less  sensibility  will  the  balance  possess.  Another  point  to 
be  taken  into  account  here  is,  that  the  moving  forces  being  equal,  a 
lesser  mass  or  weight  is  more  readily  moved  than  a greater.  (§  4 a). 

§6- 

We  will  now  proceed,  first,  to  give  the  student  a few  general  rules  to 
guide  him  in  the  purchase  of  a balance  intended  for  the  purposes  of 
quantitative  analysis ; and,  secondly,  to  pbint  out  the  best  method  of 
testing  the  accuracy  and  sensibility  of  a balance. 

1.  A balance  able  to  bear  70  or  80  grammes  in  each  scale,  suffices  for 
most  purposes. 

2.  The  balance  must  be  enclosed  in  a glass  case  to  protect  it  from  dust. 
This  case  ought  to  be  sufficiently  large,  and,  more  especially,  its  sides 
should  not  approach  too  near  the  scales.  It  must  be  constructed  in  a 
manner  to  admit  of  its  being  opened  and  closed  with  facility,  and  thus 
to  allow  the  operation  of  weighing  to  be  effected  without  any  disturbing 
influence  from  currents  of  air.  Therefore,  either  the  front  part  of  the 
case  should  consist  of  three  parts,  viz.,  a fixed  centre  part  and  two 
lateral  parts,  opening  like  doors ; or,  if  the  front  part  happens  to  be 
made  of  one  piece,  and  arranged  as  a sliding-door,  the  two  sides  of  the 
case  must  be  provided  each  with  a door. 


WEIGHING. 


13 


§7.] 

3.  The  balance  must  be  provided  with  a proper  contrivance  to  render 
it  immovable  whilst  the  weights  are  being  placed  upon  the  scale.  This  is 
most  commonly  effected  by  an  arrangement  which  enables  the  operator  to 
lift  up  the  beam  and  thus  to  remove  the  middle  edge  from  its  support, 
whilst  the  scales  remain  suspended. 

It  is  highly  advisable  to  have  the  case  of  the  balance  so  arranged  that 
the  contrivances  for  lifting  the  beam  and  fixing  the  scales  can  be  worked 
while  the  case  remains  closed,  and  consequently  from  without. 

4.  It  is  necessary  that  the  balance  should  be  provided  with  an  index  to 
mark  its  oscillations ; this  index  is  appropriately  placed  at  the  bottom  of 
the  balance. 

5.  The  balance  must  be  provided  with  a spirit  level,  to  enable  the 
operator  to  place  the  three  edges  on  an  exactly  horizontal  level ; it  is  best 
also  for  this  purpose  that  the  case  should  rest  upon  three  screws. 

6.  It  is  very  desirable  that  the  beam  should  be  graduated  into  tenths,  so 
as  to  enable  the  operator  to  weigh  the  milligramme  and  its  fractions  with 
a centigramme  “ rider.”  * 

7.  The  balance  must  be  provided  with  a screw  to  regulate  the  centre  of 
gravity,  and  likewise  with  two  screws  to  regulate  the  equality  of  the  arms, 
and  finally  with  screws  to  restore  the  equilibrium  of  the  scales,  should 
this  have  been  disturbed. 


The  following  experiments  serve  to  test  the  accuracy  and  sensibility  of 
a balance. 

1.  The  balance  is,  in  the  first  place,  accurately  adjusted,  if  necessary, 
either  by  the  regulating  screws,  or  by  means  of  tinfoil,  and  a milligramme 
weight  is  then  placed  in  one  of  the  scales.  A good  and  practically 
useful  balance  must  turn  very  distinctly  with  this  weight ; a delicate 
chemical  balance  should  indicate  the  y1^  of  a milligramme  with  perfect 
distinctness. 

2.  Both  scales  are  loaded  with  the  maximum  weight  the  construction  of 
the  balance  will  admit  of — the  balance  is  then  accurately  adjusted,  and  a 
milligramme  added  to  the  weight  in  the  one  scale.  This  ought  to  cause 
the  balance  to  turn  to  the  same  extent  as  in  1.  In  most  balances,  how- 
ever, it  shows  somewhat  less  on  the  index.  It  follows  from  §5/3  that  the 
balance  will  oscillate  more  slowly  in  this  than  in  the  first  experiment. 

3.  The  balance  is  accurately  adj  usted,  (should  it  be  necessary  to  esta- 
blish a perfect  equilibrium  between  the  scales  by  loading  the  one  with  a 
minute  portion  of  tinfoil,  this  tinfoil  must  be  left  remaining  upon  the 
scale  during  the  experiment)  ; both  scales  are  then  equally  loaded,  say, 
with  fifty  grammes  each,  and,  if  necessary,  the  balance  is  again  adjusted 
(by  the  addition  of  small  weights).  The  load  of  the  two  scales  is  then 
interchanged,  so  as  to  transfer  that  of  the  right  scale  to  the  left,  and  vice 
versd.  A balance  with  perfectly  equal  arms  must  maintain  its  absolute 
equilibrium  upon  this  interchange  of  the  weights  of  the  two  scales. 

4.  The  balance  is  accurately  adjusted  ; it  is  then  arrested  and  again  set 
in  motion  ; the  same  process  should  be  repeated  several  times.  A good 
balance  must  invariably  reassume  its  original  equilibrium.  A balance 
the  end  edges  of  which  afford  too  much  play  to  the  hook  resting  upon 

* [Becker’s  later  balances  have  beams  graduated  to  twelfths,  and  a rider  weigh- 
ing 12  mgrs.  This  enables  the  operator  to  use  nearly  the  whole  of  the  gradua- 
tion.] 


14 


OPERATIONS. 


H 8. 


them,  so  as  to  allow  the  latter  slightly  to  alter  its  position,  will  show  per- 
ceptible differences  in  different  trials.  This  fault,  however,  is  possible 
only  with  balances  of  defective  construction. 

A balance  to  be  practically  useful  for  the  purposes  of  quantitative  ana- 
lysis must  stand  the  first,  second,  and  last  of  these  tests.  A slight  in- 
equality of  the  arms  is  of  no  great  consequence,  as  the  error  that  it  would 
occasion  may  be  completely  prevented  by  the  manner  of  weighing. 


As  the  sensibility  of  a balance  will  speedily  decrease  if  the  steel  edges 
are  allowed  to  get  rusty,  delicate  balances  should  never  be  kept  in  the 
laboratory,  but  always  in  a separate  room.  It  is  also  advisable  to  place 
within  the  case  of  the  balance  a vessel  half  filled  with  calcined  carbonate 
of  potassa,  to  keep  the  air  dry.  I need  hardly  add  that  this  salt  must  be 
re-calcined  as  soon  as  it  gets  moist. 

§ 8. 

b.  The  Weights. 

1.  The  French  gramme  is  the  best  standard  for  calculation.  A set  of 
weights  ranging  from  fifty  grammes  to  one  milligramme  may  be  considered 
sufficient  for  all  practical  purposes.  With  regard  to  the  set  of  weights,  it 
is  generally  a matter  of  indifference  for  scientific  purposes  whether  the 
gramme,  its  multiples  and  fractions,  are  really  and  perfectly  equal  to  the 
accurately  adjusted  normal  weights  of  the  corresponding  denominations ; * 
but  it  is  absolutely  necessary  that  they  should  agree  perfectly  with  each 
other,  i.e.,  the  centigramme  weight  must  be  exactly  the  one  hundredth 
part  of  the  gramme  weight  of  the  set,  &c.  &c. 

2.  The  whole  of  the  set  of  weights  should  be  kept  in  a suitable,  well- 
closing box ; and  it  is  desirable  likewise  that  a distinct  compartment  be 
appropriated  to  every  one  even  of  the  smaller  weights. 

3.  As  to  the  shape  best  adapted  for  weights,  I think  that  of  short  frusta 
of  cones  inverted,  with  a handle  at  the  top,  the  most  convenient  and  prac- 
tical form  for  the  large  weights ; square  pieces  of  foil,  turned  up  at  one 
corner,  are  best  adapted  for  the  small  weights.  The  foil  used  for  this  pur- 
pose should  not  be  too  thin,  and  the  compartments  adapted  for  the  recep- 
tion of  the  several  smaller  weights  in  the  box,  should  be  large  enough  to 
admit  of  their  contents  being  taken  out  of  them  with  facility,  or  else  the 
smaller  weights  will  soon  get  cracked,  bruised,  and  indistinct.  Every 
one  of  the  weights  (with  the  exception  of  the  milligramme)  should  be 
distinctly  marked. 

4.  With  respect  to  the  material  most  suitable  for  the  manufacture  of 
weights,  we  commonly  rest  satisfied  with  having  the  smaller  weights 
only,  from  1 or  0*5  gramme  downwards,  made  of  platinum  or  aluminium 
foil,  using  brass  weights  for  all  the  higher  denominations.  Brass  weights 
must  be  carefully  shielded  from  the  contact  of  acid  or  other  vapors,  or 
their  correctness  will  be  impaired ; nor  should  they  ever  be  touched  with 
the  fingers,  but  always  with  small  pincers.  But  it  is  an  erroneous  no- 
tion to  suppose  that  weights  slightly  tarnished  are  unfit  for  use.  It  is, 


* Still  it  would  be  desirable  that  mechanicians  who  make  gramme -weights  in- 
tended for  the  use  of  the  chemist,  should  endeavor  to  procure  normal  weights. 
It  is  very  inconvenient,  in  many  cases,  to  find  notable  differences  between  weights 
of  the  same  denomination,  but  coming  from  different  makers  ; as  I myself  have 
often  had  occasion  to  discover. 


§9.] 


WEIGHING. 


15 


indeed,  hardly  possible  to  prevent  weights  for  any  very  great  length  of 
time  from  getting  slightly  tarnished.  I have  carefully  examined  many 
weights  of  this  description,  and  have  found  them  as  exactly  corresponding 
with  one  another  in  their  relative  proportions  as  they  were  when  first 
used.  The  tarnishing  coat,  or  incrustation,  is  so  extremely  thin,  that 
even  a very  delicate  balance  will  generally  fail  to  point  out  any  per- 
ceptible difference  in  the  weight. 

The  following  is  the  proper  way  of  testing  the  weights  : — 

One  scale  of  a delicate  balance  is  loaded  with  a one-gramme  weight, 
and  the  balance  is  then  completely  equipoised  by  taring  with  small 
pieces  of  brass,  and  finally  tinfoil  (not  paper,  since  this  absorbs 
moisture).  The  weight  is  then  removed,  and  replaced  successively  by 
the  other  gramme  weights,  and  afterwards  by  the  same  amount  of  weight 
in  pieces  of  lower  denominations. 

The  balance  is  carefully  scrutinized  each  time,  and  *any  deviation  from 
the  exact  equilibrium  marked.  In  the  same  way  it  is  seen  whether  the 
two-gramme  piece  weighs  the  same  as  two  single  grammes,  the  five- 
gramme  piece  the  same  as  three  single  grammes  and  the  two-gramme 
piece,  &c.  In  the  comparison  of  the  smaller  weights  thus  among  them- 
selves, they  must  not  show  the  least  difference  on  a balance  turning  with 
y-g-  of  a milligramme.  In  comparing  the  larger  weights  with  all  the  small 
ones,  differences  of  -Jg-  to  To  of  a milligramme  may  be  passed  over.  If 
you  wish  them  to  be  more  accurate,  you  must  adjust  them  yourself.  In 
the  purchase  of  weights  chemists  ought  always  to  bear  in  mind  that  an 
accurate  weight  is  truly  valuable,  whilst  an  inaccurate  one  is  absolutely 
worthless.  It  is  the  safest  way  for  the  chemist  to  test  every  weight  he 
purchases,  no  matter  how  high  the  reputation  of  the  maker. 

§ 9. 

c.  The  Process  of  Weighing. 

We  have  two  different  methods  of  determining  the  weight  of  substan- 
ces ; the  one  might  be  termed  direct  weighing , the  other  is  called  weigh- 
ing by  substitution. 

In  direct  weighing , the  substance  is  placed  upon  one  scale,  and  the 
weight  upon  the  other.  If  we  possess  a balance,  the  arms  of  which  are 
of  equal  length,  and  the  scales  in  a perfect  state  of  equilibrium,  it  is  in- 
different upon  which  scale  the  substance  is  placed  in  the  several  weigh- 
ings required  during  an  analytical  process  ; i.e .,  we  may  weigh  upon  the 
right  or  upon  the  left  side,  and  change  sides  at  pleasure,  without  en- 
dangering the  accuracy  of  our  results.  But  if,  on  the  contrary,  the  arms 
of  our  balance  are  not  perfectly  equal,  or  if  the  scales  are  not  in  a state 
of  perfect  equilibrium,  we  are  compelled  to  weigh  invariably  upon  the 
same  scale,  otherwise  the  correctness  of  our  results  will  be  more  or  less 
materially  impaired. 

Suppose  we  want  to  weigh  one  gramme  of  a substance,  and  to  divide 
this  amount  subsequently  into  two  equal  parts.  Let  us  assume  our 
balance  to  be  in  a state  of  perfect  equilibrium,  but  with  unequal  arms, 
the  left  being  99  millimetres,  the  right  100  millimetres  long;  we  place  a 
gramme  weight  upon  the  left  scale,  and  against  this,  on  the  right  scale, 
as  much  of  the  substance  to  be  weighed  as  will  restore  the  equilibrium 
of  the  balance. 

According  to  the  axiom,  “ masses  are  in  equilibrium  upon  a lever,  if 


16 


OPERATIONS. 


[§  9. 

the  products  of  their  weights  into  their  distances  from  the  fulcrum  are 
equal,”  we  have  consequently  upon  the  right  scale  0*99  grm.  of  substance, 
since  99  X 1*00=100  X 0*99.  If  we  now,  for  the  purpose  of  weighing  one 
half  the  quantity,  remove  the  whole  weight  from  the  left  scale,  substitu- 
ting a 0*5  grm.  weight  for  it,  and  then  take  off  part  of  the  substance 
from  the  right  scale,  until  the  balance  recovers  its  equilibrium,  there  will 
remain  0*495  grm. ; and  this  is  exactly  the  amount  we  have  removed 
from  the  scale : we  have  consequently  accomplished  our  object  with  re- 
spect to  the  relative  weight;  and,  as  we  have  already  remarked,  the 
absolute  weight  is  not  generally  of  so  much  importance  in  scientific  work. 
But  if  we  attempted  to  halve  the  substance  which  we  have  on  the  right 
scale,  by  first  removing  both  the  weight  and  the  substance  from  the 
scales,  and  placing  subsequently  a 0*5  grm.  weight  upon  the  right  scale, 
and  part  of  the  substance  upon  the  left,  until  the  balance  recovers  its 
equilibrium,  we  should  have  0*505  of  substance  upon  the  left  scale,  since 
100  X 0*500=99  X 0*505  ; and  consequently,  instead  of  exact  halves,  we 
should  have  one  part  of  the  substance  amounting  to  0*505,  the  other  only 
to  0*485. 

If  the  scales  of  our  balance  are  not  in  a state  of  absolute  equilibrium, 
we  are  obliged  to  weigh  our  substances  in  vessels  to  insure  accurate  re- 
sults (although  the  arms  of  the  balance  be  perfectly  equal).  It  is  self- 
evident  that  the  weights  in  this  case  must  likewise  be  invariably  placed 
upon  one  and  the  same  scale,  and  that  the  difference  between  the  two 
scales  must  not  undergo  the  slightest  variation  during  the  whole  course 
of  a series  of  experiments. 

From  these  remarks  result  the  two  following  rules : — 

1.  It  is,  under  all  circumstances,  advisable  to  place  the  substance  in- 
variably upon  one  and  the  same  scale — most  conveniently  upon  the  left. 

2.  If  the  operator  happens  to  possess  a balance  for  his  own  private  and 
exclusive  use,  there  is  no  need  that  he  should  adjust  it  at  the  commence- 
ment of  every  analysis  ; but  if  the  balance  be  used  in  common  by  several 
persons,  it  is  absolutely  necessary  to  ascertain,  before  every  operation, 
whether  the  state  of  absolute  equilibrium  may  not  have  been  disturbed. 

Weighing  by  substitution  yields  not  only  relatively , but  also  absolutely 
accurate  results ; no  matter  whether  the  arms  of  the  balance  be  of  exactly 
equal  lengths  or  not,  or  whether  the  scales  be  in  perfect  equipoise  or  not. 

The  process  is  conducted  as  follows : the  material  to  be  weighed — say 
a platinum  crucible — is  placed  upon  one  scale,  and  the  other  scale  is 
accurately  counterpoised  against  it.  The  platinum  crucible  is  then  re- 
moved, and  the  equilibrium  of  the  balance  restored  by  substituting 
weights  for  the  removed  crucible.  It  is  perfectly  obvious  that  the  sub- 
stituted weights  will  invariably  express  ’the  real  weight  of  the  crucible 
with  absolute  accuracy.  We  weigh  by  substitution  whenever  we  require 
the  greatest  possible  accuracy ; as,  for  instance,  in  the  determination  of 
atomic  weights.  The  process  may  be  materially  shortened  by  first  placing 
a tare  (which  must  of  course  be  heavier  than  the  substance  to  be 
weighed)  upon  one  scale,  say  the  left,  and  loading  the  other  scale  with 
weights  until  equilibrium  is  produced.  This  tare  is  always  retained  on 
the  left  scale.  The  weights  after  being  noted  are  removed.  The  sub- 
stance is  placed  on  the  right  scale,  together  with  the  smaller  weights  re- 
quisite to  restore  the  equilibrium  of  the  balance.  The  sum  of  the 
weights  added  is  then  subtracted  from  the  noted  weight  of  the  counter- 
poise : the  remainder  will  at  once  indicate  the  absolute  weight  of  the  sub- 


WEIGHING. 


17 


§io.i 

stance.  Let  ns  suppose,  for  instance,  we  have  on  the  left  scale  a tare 
requiring  a weight  of  fifty  grammes  to  counterpoise  it.  We  place  a 
platinum  crucible  on  the  right  scale,  and  find  that  it  requires  an  addition 
of  weight  to  the  extent  of  10  grammes  to  counterpoise  the  tare  on  the 
left.  Accordingly,  the  crucible  weighs  50  minus  10=40  grammes. 

§ 10- 

The  following  rules  will  be  found  useful  in  performing  the  process  of 
weighing : — 

1.  The  safest  and  most  expeditious  way  of  ascertaining  the  exact 
weight  of  a substance,  is  to  avoid  trying  weights  at  random ; instead  of 
this,  a strictly  systematic  course  ought  to  be  pursued  in  counterpoising 
substances  on  the  balance.  Suppose,  for  instance,  we  want  to  weigh  a 
crucible,  the  weight  of  which  subsequently  turns  out  to  be  6*627  gram- 
mes ; well,  we  place  10  grammes  on  the  other  scale  against  it,  and  we 
find  this  is  too  much ; we  place  the  weight  next  in  succession,  i.  e.,  5 
grammes,  and  find  this  too  little;  next  7,  too  much;  6,  too  little;  6*5, 
too  little;  6*7,  too  much;  6*6,  too  little;  6*65,  too  much;  6*62,  too 
little  ; 6*63,  too  much  ; 6*625,  too  little  ; 6*627,  right. 

I have  selected  here,  for  the  sake  of  illustration,  a most  complicated 
case  ; but  this  systematic  way  of  laying  on  the  weights  will  in  most  in- 
stances lead  to  the  desired  end,  in  half  the  time  required  when  weights 
are  tried  at  random.  After  a little  practice  a few  minutes  will  suffice 
to  ascertain  the  weight  of  a substance  to  within  the  y1^  of  a milligramme, 
provided  the  balance  does  not  oscillate  too  slowly. 

2.  The  milligrammes  and  fractions  of  milligrammes  are  determined  by 
a centigramme  rider  (to  be  placed  on  or  between  the  divisions  on  the 
beam)  far  more  expeditiously  and  conveniently  than  by  the  use  of  the 
weights  themselves,  and  at  the  same  time  with  equal  accuracy. 

3.  Particular  care  and  attention  should  be  bestowed  on  entering  the 
weights  in  the  book.  The  best  way  is  to  write  down  the  weights  first 
by  inference  from  the  blanks,  or  gaps  in  the  weight  box,  and  to  control 
the  entry  subsequently  by  removing  the  weights  from  the  scale,  and  re- 
placing them  in  their  respective  compartments  in  the  box.  The  student 
should  from  the  commencement  make  it  a rule  to  enter  the  number  to 
be  deducted  in  the  lower  line  / thus,  in  the  upper  line,  the  weight  of 
the  crucible  4*  the  substance ; in  the  lower  line,  the  weight  of  the  empty 
crucible. 

4.  The  balance  ought  to  be  arrested  every  time  any  change  is  contem- 
plated, such  as  removing  weights,  substituting  one  weight  for  another, 
&c.  &c.,  or  it  will  soon  get  spoiled. 

5.  Substances  (except,  perhaps,  pieces  of  metal,  or  some  other  bodies 
of  the  kind)  must  never  be  placed  directly  upon  the  scales,  but  ought  to 
be  weighed  in  appropriate  vessels  of  platinum,  silver,  glass,  porcelain, 
&c.,  never  on  paper  or  card,  since  these,  being  liable  to  attract  moisture, 
are  apt  to  alter  in  weight.  The  most  common  method  is  to  weigh  in 
the  first  instance  the  vessel  by  itself,  and  to  introduce  subsequently  the 
substance  into  it ; to  weigh  again,  and  subtract  the  former  weight  from 
the  latter.  In  many  instances,  and  more  especially  where  several  por- 
tions of  the  same  substance  are  to  be  weighed,  the  united  weight  of  the 
vessel  and  of  its  contents  is  first  ascertained ; a portion  of  the  contents 
is  then  shaken  out,  and  the  vessel  weighed  again;  the  loss  of  weight 
expresses  the  amount  of  the  portion  taken  out  of  the  vessel. 

2 


18 


OPERATIONS. 


[§H. 

6.  Substances  liable  to  attract  moisture  from  tlie  air,  must  be  weighed 
invariably  in  closed  vessels  (in  covered  crucibles,  for  instance,  or  between 
two  watch-glasses,  or  in  a closed  glass  tube) ; fluids  are  to  be  weighed  in 
small  bottles  closed  with  glass  stoppers. 

7.  A vessel  ought  never  to  be  weighed  whilst  warm,  since  it  will  in 
that  case  invariably  weigh  lighter  than  it  really  is.  This  is  owing  to 
two  circumstances.  In  the  first  place,  every  body  condenses  upon  its 
surface  a certain  amount  of  air  and  moisture,  the  quantity  of  which 
depends  upon  the  temperature  and  hygroscopic  state  of  the  air,  and 
likewise  on  its  own  temperature.  Now  suppose  a crucible  has  been 
weighed  cold  at  the  commencement  of  the  operation,  and  is  subsequently 
weighed  again  whilst  hot,  together  with  the  substance  it  contains,  and  the 
weight  of  which  we  wish  to  determine.  If  we  subtract  for  this  purpose 
the  weight  of  the  cold  crucible,  ascertained  in  the  former  instance,  from 
the  weight  found  in  the  latter,  we  shall  subtract  too  much,  and  conse- 
quently we  shall  set  down  less  than  the  real  weight  for  the  substance. 
In  the  second  place,  bodies  at  a high  temperature  are  constantly  com- 
municating heat  to  the  air  immediately  around  them  ; the  heated  air 
expands  and  ascends,  and  the  denser  and  colder  air,  flowing  towards  the 
space  which  the  former  leaves,  produces  a current  which  tends  to  raise 
the  scale,  making  it  thus  appear  lighter  than  it  really  is. 

8.  If  we  suspend  from  the  end  edges  of  a correct  balance  respectively 
10  grammes  of  platinum  and  10  grammes  of  glass,  by  wires  of  equal 
weight,  the  balance  will  assume  a state  of  equilibrium  ; but  if  we  sub- 
sequently immerse  the  platinum  and  glass  completely  in  water,  this 
equilibrium  will  at  once  cease,  owing  to  the  different  specific  gravity  of 
the  two  substances  ; since,  as  is  well  known,  substances  immersed  in 
water  lose  of  their  weight  a quantity  equal  to  the  weight  of  their  own 
bulk  of  water.  If  this  be  borne  in  mind,  it  must  be  obvious  to  every 
one  that  weighing  in  the  air ' is  likewise  defective,  inasmuch  as  the  bulk 
of  the  substance  weighed  is  not  the  same  with  that  of  the  weight.  This 
defect,  however,  is  so  very  insignificant,  owing  to  the  trifling  specific 
gravity  of  the  air  in  proportion  to  that  of  solid  substances,  that  we  may 
generally  disregard  it  altogether  in  analytical  experiments.  In  cases, 
however,  where  absolutely  accurate  results  are  required,  the  bulk  both 
of  the  substance  examined,  and  of  the  weight,  must  be  taken  into  ac- 
count, and  the  weight  of  the  corresponding  volume  of  air  added  respec- 
tively to  that  of  the  substance  and  of  the  weight,  making  thus  the  pro- 
cess equivalent  to  weighing  in  vacuo. 

§ n. 

2.  Measuring. 

The  process  of  measuring  is  confined  in  analytical  researches  mostly  to 
gases  and  liquids.  The  method  of  measuring  gases  has  been  brought  to 
such  perfection  that  it  may  be  said  to  equal  in  accuracy  the  method  of 
weighing.  However,  such  accurate  measurements  demand  an  expendi- 
ture of  time  and  care,  which  can  be  bestowed  only  on  the  nicest  and  most 
delicate  scientific  investigations.* 

* [The  student  who  will  practise  the  accurate  measurement  of  gases  in  any  but 
the  simplest  cases,  must  refer  for  all  details  to  Bunsen’s  ‘ ‘ G-asometry  ” (trans- 
lated by  Roscoe),  and  Russell,  Jour.  Chem.  Soc.,  1868  p.  128,  as  the  subject  is 
too  extensive  for  the  limits  of  this  volume.  ] 


MEASURING. 


19 


§12.] 


The  measuring  of  liquids  in  analytical  investigations  was  resorted  to 
first  by  Descroizilles  (“  Alkalimeter,”  1806).  Gay-Lussac  materially 
improved  the  process,  and  indeed  brought  it  to  the  highest  degree  of 
perfection  (measuring  of  the  solution  of  chloride  of  sodium  in  the  assay 
of  silver  in  the  wet  way).  More  recently  F.  Mohr*  has  bestowed  much 
care  and  ingenuity  upon  the  production  of  appropriate  and  convenient 
measuring  apparatus,  and  has  added  to  our  store  the  eminently  practical 
compression  stop-cock  burette.  The  process  is  now  resorted  to  even  in 
most  accurate  scientific  investigations,  since  it  requires  much  less  time 
than  the  process  of  weighing. 

The  accuracy  of  all  measurings  depends  upon  the  proper  construction 
of  the  measuring  vessels,  and  also  upon  the  manner  in  which  the  process 
is  conducted. 


u.  The  Measuring  of  Gases, 

We  use  for  the  measuring  of  gases  graduated  tubes  of  greater  or  less 
capacity,  made  of  strong  glass,  and  closed  by  fusion  at  one  end,  which 
should  be  rounded.  The  following  tubes  will  be  found  sufficient  for  all 
the  processes  of  gas  measuring  required  in  organic  elementary  analyses. 

1.  A bell-glass  capable  of  holding  from  150  to  250  c.  c.,  and  about  4 
centimetres  in  diameter ; divided  into  cubic  centimetres. 

2.  Five  or  six  glass  tubes,  about  12  to  15  millimetres  in  diameter  in 
the  clear,  and  capable  of  holding  from  30  to  40  c.  c,  each,  divided  into 
\ c.  c. 

The  sides  of  these  tubes  should  be  pretty  thick,  otherwise  they  will 
be  liable  to  break,  especially  when  used  to  measure  over  mercury.  The 
sides  of  the  bell-glass  should  be  about  3,  of  the  tubes  about  2 millimetres 
thick. 

The  most  important  point,  however,  in  connection  with  measuring  in- 
struments is  that  the}”  be  correctly  graduated,  since  upon  this  of  course 
depends  the  accuracy  of  the  results.  For  the  method  of  graduating  I 
refer  to  Greville  Williams’  “Chemical  Manipulation.”  f 

In  testing  the  measuring  tubes  we  have  to  consider  three  things. 

1.  Do  the  divisions  of  a tube  correspond  with  each  other? 

2.  Do  the  divisions  of  each  tube  correspond  with  those  of  the  other 
tubes  ? 

3.  Do  the  volumes  expressed1'  by  the  graduation  lines  correspond  with 
the  weights  used  by  the  anatyst  ? 

These  three  questions  are  answered  by  the  following  experiments : 

a.  The  tube  which  it  is  intended  to  examine  is  placed  in  a perpendicu- 
lar position,  and  filled  gradually  with  accurately  measured  small  quanti- 
ties of  mercury,  care  being  taken  to  ascertain  with  the  utmost  precision 
whether  the  graduation  of  the  tube  is  proportionate  to  the  equal  vol- 
umes of  mercury  poured  in.  The  measuring-off  of  the  mercury  is  effected 
by  means  of  a small  glass  tube,  sealed  at  one  end,  and  ground  perfectly 
even  and  smooth  at  the  other.  This  tube  is  filled  to  overflowing  by  im- 
mersion under  mercury,  care  being  taken  to  allow  no  air  bubbles  to 


* “ Lehrbuch  der  Titrirmethode,”  by  Dr.  Fr.  Mohr.  Brunswick,  1855. 
f [See  also  Cary  Lea,  Am.  Jour.  Sci.  and  Arts,  2d  ser. , vol.  42,  p.  375.] 


OPERATIONS. 


20 


L§  13. 


remain  in  it ; the  excess  of  mercury  is  then  removed  by  pressing  a small 
glass  plate  down  on  the  smooth  edge  of  the  tube.* 

b.  Different  quantities  of  mercury  are  successively  measured  off  in  one 
o£  the  smaller  tubes,  and  then  transferred  into  the  other  tubes.  The  tubes 
may  be  considered  in  perfect  accordance  with  each  other,  if  the  mer- 
cury reaches  invariably  the  same  divisional  point  in  every  one  of  them. 

Such  tubes  as  are  intended  simply  to  determine  the  relative  volume  of 
different  gases,  need  only  pass  these  two  experiments  ; but  in  cases  where 
we  want  to  calculate  the  weight  of  a gas  from  its  volume , it  is  necessary 
also  to  obtain  an  answer  to  the  third  question.  For  this  purpose — 

c.  One  of  the  tubes  is  accurately  weighed  and  then  filled  with  distilled 
water  of  a temperature  of  16°  to  the  last  mark  of  the  graduated  scale; 
the  weight  of  the  water  is  then  accurately  determined.  If  the  tube 
agrees  with  the  weights,  every  100  c.  c.  of  water  of  16°  must  weigh  99'9 
grm.  But  should  it  not  agree,  no  matter  whether  the  error  lie  in  the 
graduation  of  the  tube  or  in  the  adjustment  of  the  weights,  we  must  ap- 
ply a correction  to  the  volume  observed  before  calculating  the  weight  of 
a gas  therefrom.  Let  us  suppose,  for  instance,  that  we  find  100  c.  c.  td 
weigh  only  99’6  grm. : assuming  our  weights  to  be  correct,  the  c.  c.  of 
our  scale  are  accordingly  too  small ; and  to  convert  100  of  these  c.c.  into 
normal  c.  c.  we  say : — 

99-9  : 99*6  : : 100  : a;. 

In  the  measuring  of  gases  we  must  have  regard  to  the  following 
points  : — 

1.  Correct  reading-off.  2.  The  temperature  of  the  gas.  3.  The  degree 
of  pressure  operating  upon  it.  And  4.  The  circumstance  whether  it  is 
dry  or  moist.  The  three  latter  points  will  be  readily  understood,  if  it 
be  borne  in  mind  that  any  alteration  in  the  temperature  of  a gas,  or  in 
the  pressure  acting  upon  it,  or  in  the  tension  of  the  admixed  aqueous 
vapor,  involves  likewise  a considerable  alteration  in  its  volume. 


§ 13- 

1.  Correct  Beading-off. 

This  is  rather  difficult,  since  mercury  in  a cylinder  has  a convex  sur- 
face (especially  observable  with  a narrow  tube),  owing  to  its  own  cohe- 
sion ; whilst  water,  on  the  other  hand,  under  the  same  circumstances  has 
a concave  surface,  owing  to  the  attraction  which  the  walls  of  the  tube 
exercise  upon  it.  The  cylinder  should  invariably  be  placed  in  a perfectly 
perpendicular  position,  and  the  eye  of  the  operator  brought  to  a level  with 
the  surface  of  the  fluid. 

In  reading-off  over  water,  the  middle  of  the  dark  zone  formed  by  that 
portion  of  the  liquid  that  is  drawn  up  around  the  inner  walls  of  the 
tube,  is  assumed  to  be  the  real  surface  ; whilst  when  operating  with 
mercury,  we  have  to  place  the  real  surface  in  a plane  exactly  in  the 
middle  between  the  highest  point  of  the  surface  of  the  mercury,  and 
the  points  at  which  the  latter  is  in  actual  contact  with  the  walls  of  the 
tube.  However,  the  results  obtained  in  this  way  are  only  approximate. 

Absolutely  accurate  results  cannot  be  arrived  at,  in  measuring  over 

* As  warming  the  metal  is  to  be  carefully  avoided  in  this  process,  it  is  advi- 
sable not  to  hold  the  tube  with  the  hand  in  immersing  it  in  the  mercury,  but  ta 
fasten  it  in  a small  wooden  holder. 


MEASURING  OF  GASES. 


21 


83  u>  15-1 

water  or  any  other  fluid  that  adheres  to  glass.  But  over  mercury  they 
may  be  arrived  at  if  the  error  of  the  meniscus  be  determined  and  the 
mercury  be  read  off  at  the  highest  point.  The  determination  of  the  error 
of  the  meniscus  is  performed  for  each  tube,  once  for  all,  in  the  following 
manner  : some  mercury  is  poured  into  the  tube,  and  its  height  read-off 
right  on  a level  with  the  top  of  the  convex  surface  exhibited  by  it ; a few 
drops  of  solution  of  chloride  of  mercury  are  then  poured  on  the  top  of  the 
metal ; this  causes  the  convexity  to  disappear  ; the  height  of  the  mercury 
in  the  tube  is  now  read-off  again  and  the  difference  noted.  In  the  process 
of  graduation,  the  tube  stands  upright,  in  that  of  measuring  gases,  it  is 
placed  upside  down ; the  difference  observed  must  accordingly  be  doubled, 
and  the  sum  added  to  each  volume  of  gas  read  off. 

§ i t- 

2.  Influence  of  Temperature. 

The  temperature  of  gases  to  be  measured  is  determined  either  by 
making  it  correspond  with  that  of  the  confining  fluid,  and  ascertaining 
the  latter,  or  by  suspending  a delicate  thermometer  by  the  side  of  the 
gas  to  be  measured,  and  noting  the  degree  which  it  indicates. 

If  the  construction  of  the  pneumatic  apparatus  permits  the  total  im- 
mersion of  the  cylinder  in  the  confining  fluid,  uniformity  of  tempe- 
rature between  the  latter  and  the  gas  which  it  is  intended  to  measure, 
is  most  readily  and  speedily  obtained  ; but  in  the  reverse  case,  the 
operator  must  always,  after  every  manipulation,  allow  half  an  hour  or, 
in  operations  combined  with  much  heating,  even  an  entire  hour  to  elapse, 
before  proceeding  to  observe  the  state  of  the  mercury  in  the  cylinder, 
and  in  the  thermometer. 

Proper  care  must  also  be  taken,  after  the  temperature  of  the  gas  has 
been  duly  adjusted,  to  prevent  re-expansion  during  the  reading-off ; all 
injurious  influences  in  this  respect  must  accordingly  be  carefully  guarded 
against,  and  the  operator  should,  more  especially,  avoid  laying  hold  of 
the  tube  with  his  hand  (in  pressing  it  down,  for  instance,  into  the  con- 
fining fluid)  ; making  use,  instead,  of  a wooden  holder. 

§ 15. 

3.  Influence  of  Pressure. 

With  regard  to  the  third  point,  the  gas  is  under  the  actual  pressure  of 
the  atmosphere  if  the  confining  fluid  stands  on  an  exact  level  both  in  and 
outside  the  cylinder;  the  degree  of  pressure  exerted  upon  it  may  therefore 
at  once  be  ascertained  by  consulting  the  barometer.  But  if  the  confining 
fluid  stands  higher  in  the  cylinder  than  outside,  the  gas  is  under  less 
pressure, — if  lower , it  is  under  greater  pressure  than  that  of  the  atmo- 
sphere ; in  the  latter  case,  the  perfect  level  of  the  fluid  inside  and  outside 
the  cylinder  may  readily  be  restored  by  raising  the  tube ; if  the  fluid 
stands  higher  in  the  cylinder  than  outside,  the  level  may  be  restored  by 
depressing  the  tube  ; this  however  can  only  be  done  in  cases  where  we 
have  a trough  of  sufficient  depth.  When  operating  over  water,  the  level 
may  in  most  cases  be  readily  adjusted  ; when  operating  over  mercury,  it 
is,  more  especially  with  wide  tubes,  often  impossible  to  bring  the  fluid  to 
a perfect  level  inside  and  outside  the  c}dinder. 


22 


OPERATIONS. 


[88  w,  ir,  ia 


§ is. 

4.  Influence  of  Moisture. 

In  measuring  gases  saturated  with  aqueous  vapor,  it  must  be  taken 
into  account  that  the  vapor,  by  virtue  of  its  tension,  exerts  a pressure 
upon  the  confining  fluid.  The  necessary  correction  is  simple,  since  we 
know  the  respective  tension  of  aqueous  vapor  for  the  various  degrees  of 
temperature.  But  before  this  correction  can  be  applied,  it  is,  of  course, 
necessary  that  the  gas  should  be  actually  saturated  with  the  vapor.  11 
is,  therefore,  indispensable  in  measuring  gases  to  take  care  to  have  the 
gas  thoroughly  saturated  with  aqueous  vapor,  or  else  absolutely  dry. 


It  is  quite  obvious  from  the  preceding  remarks,  that  volumes  of  gases 
can  be  compared  only  if  measured  at  the  same  temperature,  under  the 
same  pressure,  and  in  the  same  hygroscopic  state.  They  are  generally 
reduced  to  0°,  0*76  met.  barometer,  and  absolute  dryness.  How  this  is 
effected,  as  well  as  the  manner  in  which  we  deduce  the  weight  of  gases 
from  their  volume,  will  be  found  in  the  chapter  on  the  calculation  of 
analyses. 


§ 17. 

b.  The  Measuring  of  Fluids. 

In  consequence  of  the  vast  development  which  volumetric  analysis  has 
of  late  acquired,  the  measuring  of  fluids  has  become  an  operation  of  very 
frequent  occurrence.  According  to  the  different  objects  in  view,  various 
kinds  of  measuring  vessels  are  employed.  The  operator  must,  in  the 
case  of  every  measuring  vessel,  carefully  distinguish  whether  it  is 
graduated  for  holding  or  for  delivering  the  exact  number  of  c.  c.  marked 
on  it.  If  you  have  made  use  of  a vessel  of  the  former  description  in 
measuring  off  100  c.  c.  of  a fluid,  and  wish  to  transfer  the  latter  com- 
pletely to  another  vessel,  you  must,  after  emptying  your  measuring 
vessel,  rinse  it,  and  add  the  rinsings  to  the  fluid  transferred ; whereas, 
if  you  have  made  use  of  a measuring  vessel  of  the  latter  description, 
there  must  be  no  rinsing. 

a.  Measuring  vessels  graduated  for  holding  the  exact  measure 

OF  FLUID  MARKED  ON  THEM. 


aa.  Measuring  vessels  which  serve  to  measure  out  one  definite  quantity 
of  fluid. 

We  use  for  this  purpose — 


§ 18- 

1;  Measuring  Flasks. 

Fig.  2 represents  a measuring  flask  of  the  most  practical  and  con- 
venient form. 

Measuring  flasks  of  various  sizes  are  sold  in  the  shops,  holding 
respectively  200,  250,  500,  1000,  2000,  &c.,  c.  c.  As  a general  rule,  they 
have  no  ground-glass  stoppers ; it  is,  however,  very  desirable,  in  certain 
cases,  to  have  measuring  flasks  with  ground  stoppers.  The  flasks  must 
be  made  of  well-annealed  glass  of  uniform  thickness,  so  that  fluids  may 


§18.] 


MEASURING  OF  FLUIDS. 


23 


be  heated  in  them.  The  line-mark  should  be  placed  within  the  lower 
third,  or  at  least  within  the  lower  half,  of  the  neck. 

Measuring  llasks,  before  they  can  properly  be  employed  in  analytical 
operations,  must  first  be  carefully  tested.  The  best  and  simplest  way 
of  effecting  this  is  to  proceed  thus : — Put  the  flask, 
perfectly  dry  inside  and  outside,  on  the  one  scale  of 
a sufficiently  delicate  balance,  together  with  a weight  of 
1000  grm.  in  the  case  of  a litre  flask,  500  grm.  in  the 
case  of  a half-litre  flask,  &c.,  restore  the  equilibrium  by 
placing  the  requisite  quantity  of  shot  and  tinfoil  on  the 
other  scale,  then  remove  the  flask  and  the  weight  from 
the  balance,  put  the  flask  on  a perfectly  level  surface, 
and  pour  in  distilled  water  of  16°,*  until  the  lower 
border  of  the  dark  zone  formed  by  the  top  of  the 
water  around  the  inner  walls  corresponds  with  the 
line-mark.  After  having  thoroughly  dried  the  neck 
of  the  flask  above  the  mark,  replace  it  upon  the  scale  : 
if  this  restores  the  perfect  equilibrium  of  the  balance, 
the  water  in  the  flask  weighs,  in  the  case  of  a litre- 
measure,  exactly  1000  grm.  If  the  scale  bearing  the 
flask  sinks,  the  water  in  it  weighs  as  much  above  1000 
grm.  as  the  additional  weights  amount  to  which  you  have  to  put  in  the 
other  scale  to  restore  the  equilibrium  ; if  it  rises,  on  the  other  hand, 
the  water  weighs  as  much  less  as  the  weights  amount  to  which  you 
have  to  put  in  the  scale  with  the  flask  to  effect  the  same  end. 

If  the  water  in  the  litre-measure  weighs  999  grm.,|  in  the  half-litre 
measure,  499*5  grm.,  &c.,  the  measuring  flasks  are  correct.  Differences 
up  to  0*100  grm.,  in  the  litre  measure,  up  to  0*070  grm.  in  the  half-litre 
measure,  and  up  to  0*050  grm.  in  the  quarter-litre  measure,  are  not 
taken  into  account,  as  one  and  the  same  measuring-flask  will  be  found 
to  offer  variation  to  the  extent  indicated,  in  repeated  consecutive  weigh- 
ings, though  filled  each  time  exactly  up  to  the  mark  with  water  of  the 
same  temperature. 

Though  a flask  should,  upon  examination,  turn  out  not  to  hold  the 
exact  quantity  of  water  which  it  is  stated  to  contain,  it  may  yet  possibly 
agree  with  the  other  measuring  vessels,  and  may  accordingly  still  be 
perfectly  fit  for  use  for  most  purposes.  Two  measuring  vessels  agree 
among  themselves  if  the  marked  Nos.  of  c.  c.  bear  the  same  propor- 

* To  use  water  in  the  state  of  its  highest  density,  viz.,  of  4°,  1 c.  c.  of  which 
weighs  exactly  1 grm.,  and,  accordingly,  1 litre,  exactly  1000  grms.,  is  less  prac- 
tical, as  the  operations  must  in  that  case  be  conducted  in  a room  as  cold ; since, 
in  a warmer  room,  the  outside  of  the  flask  would  immediately  become  covered 
with  moisture,  in  consequence  of  the  air  cooling  below  dew-point.  Nor  can  I 
recommend  F.  Mohr’s  suggestion  to  make  litre-flasks,  and  measuring  vessels  in 
general,  upon  a plan  to  make  the  litre-flask,  for  instance,  hold,  not  1000  grm. 
water  at  4°,  but  1000  grm.  at  16°,  since  in  an  arrangement  of  the  kind  proper 
regard  is  not  paid  to  the  actual  meaning  of  the  term  “ litre  ” in  the  scientific 
world  ; and  measuring-vessels  of  the  same  nominal  capacity,  made  by  different 
instrument-makers,  are  thus  liable  to  differ  to  a greater  or  less  extent . One  litre- 
flask,  according  to  Mohr,  holds  1001  2 standard  c.  c.  I consider  it  impractical 
to  give  to  the  c . c . another  signification  in  vessels  intended  for  measuring  fluids 
than  in  vessels  used  for  the  measuring  of  gases,  which  latter  demand  strict  ad- 
hesion to  the  standard  c . c . , as  it  is  often  required  to  deduce  the  weight  of  a 
gas  by  calculating  from  the  volume. 

f With  absolute  accuracy,  998*981  grm. 


24 


OPERATIONS. 


tion  to  each,  other  as  the  weights  found  ; thus,  for  instance,  supposing 
your  litre-measure  to  hold  998  grin,  water  of  16°,  and  your  50  c.  c. 
pipette  to  deliver  49 '9  grm.  water  of  the  same  temperature,  the  two 
measures  agree,  since 

1000  : 50  = 998  : 49-9. 

To  prepare  or  correct  a measuring  flask,  tare  the  dry  litre,  half  litre, 
or  quarter-litre  flask,  and  then  weigh  into  it,  by  substitution  (§  9) 
999  grm.,  or,  as  the  case  may  be,  the  half  or  quarter  of  that  quantity  of 
distilled  water  of  16°.  Put  the  flask  on  a perfectly  horizontal  support, 
place  your  eye  on  an  exact  level  with  the  surface  of  the  water,  and  mark 
the  lower  border  of  the  dark  zone  by  two  little  dots  made  on  the  glass 
with  a point  dipped  into  thick  as*pkaltum  varnish,  or  some  other  sub- 
stance of  the  kind.  Now  pour  out  the  water,  place  the  flask  in  a con- 
venient position,  and  cut  with  a diamond  a fine  distinct  line  into  the 
glass  from  one  dot  to  the  other. 


bb.  Measuring  vessels  which  serve  to  measure  out  any  quantities  of 
fuid  at  will. 

S 19. 


2.  The  Graduated  Cylinder. 


This  instrument,  represented  in  fig.  3,  should  be  from  2 
to  3 cm.  wide,  of  acapacity  of  100 — 300  c.  c.,  and  divided 
into  single  c.  c.  It  must  be  ground  at  the  top,  that  it  may 
be  covered  quite  close  with  a ground-glass  plate.  The 
measuring  with  such  cylinders  is  not  quite  so  accurate  as 
with  measuring  flasks,  as  in  the  latter  the  volume  is  read 
off  in  a narrower  part.  The  accuracy  of  measuring  cylin- 
ders may  be  tested  in  the  same  way  as  in  the  case  of  mea- 
suring flasks,  viz.,  by  weighing  into  them  water  of  16°; 
or,  also,  very  well,  by  letting  definite  quantities  of  fluid 
flow  into  the  cylinder  from  a correct  pipette,  or  burette 
graduated  for  delivering,  and  observing  whether  or  not  they 
are  correctly  indicated  by  the  scale  of  the  cylinder. 


Fig.  3. 


/3.  Measuring  vessels  graduated  for  delivering  the 
exact  measure  of  fluid  marked  on  them  (graduated  & 
Vecoulement). 


aa.  Measuring  vessels  which  serve  to  measure  out  one  definite  quern- 
tity  of  fluid. 

§ 20. 

3.  The  Graduated  Pipette. 


This  instrument  serves  to  take  out  a definite  volume  of  a fluid  from 
one  vessel,  and  to  transfer  it  to  another ; it  must  accordingly  be  of  a 
suitable  shape  to  admit  of  its  being  freely  inserted  into  flasks  and  bottles. 

We  use  pipettes  of  1,  5,  10,  20,  50,  100,  150,  and  200  c.  c.  capacity. 
The  proper  shape  for  pipettes  up  to  20  c.  c.  capacity  is  represented  in 
fig.  4 ; fig.  5 shows  the  most  practical  form  for  larger  ones.  To  fill  a 


MEASURING  OF  FLUIDS. 


25 


20.] 


pipette  suction  is  applied  to  the  upper  aperture,  either  directly  with  the 
lips  or  through  a caoutchouc-tube,  until  the  fluid  stands  above  the  mark  ; 
the  upper  orifice  (which  is  somewhat  narrowed  and  ground)  is  then 
closed  with  the  first  finger  of  the  right 
hand  (the  point  of  which  should  be  a 
little  moist) ; the  outside  is  then  wiped 
dry,  if  required,  and,  the  pipette  being 
held  in  a perfectly  vertical  direction, 
the  fluid  is  made  to  drop  out,  by  lift- 
ing the  finger  a little,  till  it  has  fallen 
to  the  required  level ; the  loose  drop  is 
carefully  wiped  off,  and  the  contents  of 
the  tube  are  then  finally  transferred  to 
the  other  vessel.  In  this  process  it  is 
found  that  the  fluid  does  not  run  out 
completely,  but  that  a small  portion  of 
it  remains  adhering  to  the  glass  in  the 
point  of  the  pipette;  after  a time,  as 
this  becomes  increased  by  other  minute 
particles  of  fluid  trickling  down  from  the 
upper  part  of  the  tube,  a drop  gathers 
at  the  lower  orifice,  which  may  be  al- 
lowed to  fall  off  from  its  own  weight, 
or  may  be  made  to  drop  off  by  a slight 
shake.  If,  after  this,  the  point  of  the 
pipette  be  laid  against  a moist  portion 
of  the  inner  side  of  the  vessel,  another 
minute  portion  of  fluid  will  trickle  out, 
and,  lastly,  another  trifling  droplet  or  so 
may  be  got  out  by  blowing  into  the  pi- 
pette. Now,  supposing  the  operator 
follows  no  fixed  rule  in  this  respect,  let- 
ting the  fluid,  for  instance,  in  one  opera- 
tion simply  run  out,  whilst  in  another 
operation  he  lets  it  drain  afterwards, 
and  in  a third  blows  out  the  last  parti- 
cles of  it  from  the  pipette,  it  is  evident 
that  the  respective  quantities  of  fluid 
delivered  in  the  several  operations  can-  Fig.  4.  Fig.  5.  Fig.  6. 
not  be  quite  equal.  I prefer  in  all  cases 

the  second  method,  viz.,  to  lay  the  point  of  the  pipette,  whilst  draining, 
finally  against  a moist  portion  of  the  side  of  the  vessel,  which  I have 
always  found  to  give  the  most  accurately  corresponding  measurements. 

The  correctness  of  a pipette  is  tested  by  filling  it  up  to  the  mark  with 
distilled  water  of  16°,  letting  the  water  run  out,  in  the  manner  just 
stated,  into  a tared  vessel,  and  weighing ; the  pipette  may  be  pro- 
nounced correct  if  100  c.  c.  of  water  of  16°  weigh  99*9  grm. 

Testing  in  like  manner  the  accuracy  of  the  measurements  made  with 
a simple  hand  pipette,  we  find  that  one  and  the  same  pipette  will  in 
repeated  consecutive  weighings  of  the  contents,  though  filled  and  emptied 
each  time  with  the  minutest  care,  show  differences  up  to  0*010  grm.  for 
10  c.  c.  capacity,  up  to  0*040  grm.  for  50  c.  c.  capacity. 

The  accuracy  of  the  measurements  made  with  a pipette  may  be 


OPERATIONS. 


26 


tl  21 


heightened  by  giving  the  instrument  the  form  and  construction  shown  in 
fig.  6,  and  fixing  it  to  a holder. 

It  will  be  seen  from  the  drawing  that  these  pipettes  are  emptied  only 
to  a certain  mark  in  the  lower  tube,  and  that  they  are  provided  with 
a compression  stop-cock , a contrivance  which  we  shall  have  occasion  to 
describe  in  detail  when  on  the  subject  of  burettes.  This  contrivance 
reduces  the  differences  of  measurements  with  one  and  the  same  50  c.  c. 
pipette  to  0-005  grm. 

Pipettes  are  used  more  especially  in  cases  where  it  is  intended  to 
estimate  different  constituents  of  a substance  in  separate  portions  of  the 
same  : for  instance,  10  grm.  of  the  substance  under  examination  are  dis- 
solved in  a 250  c.  c.  flask,  the  solution  is  diluted  up  to  the  mark,  shaken, 
and  2,  3,  or  4 several  portions  are  then  taken  out  with  a 50  c.  c.  pipette. 
Each  portion  consists  of  i part  of  the  whole,  and  accordingly  contains  2 
grm.  of  the  substance.  Of  course  the  pipette  and  the  flask  must  be  in 
perfect  harmony.  Whether  they  are  may  be  ascertained  by,  for  instance, 
emptying  the  50  c.  c.  pipette  5 times  into  the  250  c.  c.  flask,  and  observ- 
ing if  the  lower  edge  of  the  dark  zone  of  fluid  coincides  with  the  mark. 
If  it  does  not,  you  may  make  a fresh  mark,  which,  no  matter  whether 
it  is  really  correct  or  not,  will  bring  the  two  instruments  in  question 
into  conformity  with  each  other. 

Cylindrical  pipettes,  graduated  throughout  their  entire  length,  may  be 
used  also  to  measure  out  any  given  quantities  of  liquid  ; however,  these 
instruments  can  properly  be  employed  only  in  processes  where  minute 
accuracy  is  not  indispensable,  as  the  limits  of  error  in  reading  off  the 
divisions  in  the  wider  part  of  the  tube  are  not  inconsiderable.  For 
smaller  quantities  of  liquid  this  inaccuracy  may  be  avoided,  by  making 
the  pipettes  of  tubes  of  uniform  width,  having  a small  diameter  only, 
and  narrowed  at  both  ends.  (Fr.  Mohr’s  measuring  pipettes.) 

When  a fluid  runs  out  of  a pipette,  drops  sometimes  remain  here  and 
there  adhering  to  the  tube  ; this  arises  from  a film  of  fat  on  the  inside ; 
it  may  be  removed  by  keeping  the  instrument  some  time  filled  with  a 
solution  of  bichromate  of  potassa  mixed  with  sulphuric  acid. 


bb.  Measuring  vessels  which  serve  to  measure  out  quantities  of  fluid  at 
will. 


4.  The  Burette . 

Of  the  various  forms  and  dispositions  of  this  instrument,  the  following 
appear  to  me  the  most  convenient : — , 


§ 21. 

I.  Mohr’s  Burette , (Compression  cock  burette.) 

For  this  excellent  measuring  apparatus,  which  is  represented  in  fig.  7, 
we  are  indebted  to  Fr.  Mohr.  It  consists  of  a cylindrical  tube,  nar- 
rower towards  the  lower  end  for  about  an  inch,  with  a slight  widening, 
however,  at  the  extreme  point,  in  order  that  the  caoutchouc  connector 
may  take  a firm  hold.  I only  use  burettes  of  two  sizes,  viz.,  of  30  c.  c., 
divided  into  To  C-  C-  ; and  of  50  c.  c.  divided  into  % c.  c.  The  former  I 
employ  principally  in  scientific,  the  latter  chiefly  in  technical  investi* 


MEASURING  OF  FLUIDS* 


27 


§21.] 

gations.  The  usual  length  of  my  30  c.  c.  burette  is  about  50  cm. ; the 
graduated  portion  occupies  about  49  cm.  The  diameter  of  the  tube  is 
accordingly  about  10  mm.  in  the  clear;  the  upper  orifice  is,  for  the  con- 
venience of  filling,  widened  in  form  of  a funnel,  measuring  20  mm.  in 
diameter;  the  width  of  the  lower  orifice  is  5 mm.  For  very  delicate 
processes,  the  length  of  the  graduated  portion  may  be  extended  to  50  or 
52  cm.,  leaving  thus  intervals  of  nearly  2 mm.  between  the  small  divi- 
sional lines.  In  my  50  c.  c.  burettes  the  graduated  portion  of  the  tub© 
is  generally  40  cm.  long. 


To  make  the  instrument  ready  for  use,  the  narrowed  lower  end  of  the 
tube  is  warmed  a little,  and  greased  with  tallow ; a caoutchouc  tube, 
about  30  mm.  long,  and  having  a diameter  of  3 mm.  in  the  clear,  is  then 
drawn  over  it ; into  the  other  end  of  this  is  inserted  a tube  of  pretty 
thick  glass,  about  40  mm.  long,  and  drawn  out  to  a tolerably  fine  point ; 
it  is  advisable  to  slightly  widen  the  upper  end  of  this  tube  also,  and  to 


28 


OPERATIONS. 


cover  it  with  a thin  coat  of  tallow ; and  also  to  tie  linen-thread,  or  twine, 
round  both  ends  of  the  connector,  to  insure  perfect  tightness. 

The  space  between  the  lower 
orifice  of  the  burette  and  the 
upper  orifice  of  the  small  deli- 
very tube  should  be  about  15 
mm.  The  india-rubber  tube  is 
now  pressed  together  between 
the  ends  of  the  tubes  by  the 
compression-cock  (or  clip).  This 
latter  instrument  is  usually  made 
out  of  brass  wire ; the  form  re- 

A good  clip  must  pinch  so  tight  that  not  a particle  of  fluid  can  make 
its  way  through  the  connector  when  compressed  by  it ; it  must  be  so  con- 
structed that  the  analyst  may  work  it  with  perfect  facility  and  exactness, 
so  as  to  regulate  the  outflow  of  the  liquid  with  the  most  rigorous  accu- 
racy, by  bringing  a higher  or  less  degree  of  pressure  to  bear  upon  it. 

For  supporting  Mohr’s  burettes,  I use  the  holder  represented  in  fig. 
7 ; this  instrument,  whilst  securely  confining  the  tube,  permits  its  being 
moved  up  and  down  with  perfect  freedom,  and  also  its  being  taken  out, 
without  interfering  with  the  compression  cock.  The  position  of  the  bu- 
rette must  be  strictly  perpendicular,  to  insure  which,  care  must  be  taken 
to  have  the  grooves  of  the  cork  lining,  which  are  intended  to  receive  the 
tube,  perfectly  vertical,  with  the  lower  board  of  the  stand  in  a horizon- 
tal position. 

To  charge  the  burette  for  a volumetrical  operation,  the  point  of  the 
instrument  is  immersed  in  the  liquid,  the  compression-cock  opened,  and 
a little  liquid,  sufficient  at  least  to  reach  into  the  burette  tube,  sucked 
up  by  applying  the  mouth  to  the  upper  end ; the  cock  is  then  closed,  and 
the  liquid  poured  into  the  burette  until  it  reaches  up  to  a little  above 
the  top  mark.  The  burette  having,  if  required,  been  duly  adjusted  in 
the  proper  vertical  position,  the  liquid  is  allowed  to  drop  out  to  the  ex- 
act level  of  the  top  mark.  The  instrument  is  now  ready  for  use.  When 
as  much  liquid  has  flowed  out  as  is  required  to  attain  the  desired  object, 
the  analyst,  before  proceeding  to  read  off  the  volume  used,  has  to  wait  a 
few  minutes,  to  give  the  particles  of  fluid  adhering  to  the  sides  of  the 
emptied  portion  of  the  tube  proper  time  to  run  down.  This  is  an  indis- 
pensable part  of  the  operation  in  accurate  measurements,  since,  if  neg- 
lected, an  experiment  in  which  the  standard  liquid  in  the  burette  is  added 
slowly  to  the  fluid  under  examination  (in  which,  accordingly,  the  minute 
particles  of  fluid  adhering  to  the  glass  have  proper  time  afforded  them 
during  the  operation  itself  to  run  down),  will,  of  course,  give  slightly 
different  results  from  those  arrived  at  in  another  experiment,  where  the 
larger  portion  of  the  standard  fluid  is  applied  rapidly,  and  the  last  few 
drops  alone  are  added  slowly. 

The  way  in  which  the  reading-off  is  effected,  is  a matter  of  great  im- 
portance in  volumetric  analysis ; the  first  requisite  is  to  bring  the  eye  to 
a level  with  the  top  of  the  fluid.  We  must  consequently  settle  the  ques- 
tion— What  is  to  be  considered  the  top  ? 

If  you  hold  a burette,  partly  filled  with  water,  between  the  eye  and  a 
strongly  illumined  wall,  the  surface  of  the  fluid  presents  the  appearance 
shown  in  fig.  10  ; if  you  hold  close  behind  the  tube  a sheet  of  white  paper, 


presented  in  fig.  8 was  given  by  Mohr. 


MEASURING  OF  FLUIDS. 


29 


§21.1 

with  a strong  light  falling  on  it,  the  surface  of  the  fluid  presents  the  appear- 
ance  shown  in  tig.  9. 

In  the  one  as  welj.  as  in  the  other  case,  you  have  to  read  off  at  the  lower 
border  of  the  dark  zone,  this  being  the  most  distinctly  marked  line.  Fr. 
Mohr  recommends  the  following  device  for  reading-off : — Paste  on  a sheet 
of  very  white  paper  a broad  strip  of  black  paper,  and,  when  reading-off, 
hold  this  close  behind  the  burette,  in  a position  to  place  the  border  line 
between  white  and  black  from  2 to  3 mm.  below  the  lower  border  of  the 
dark  zone,  as  shown  in  fig.  1 1 ; read-off  at  the  lower  border  of  the  dark 
zone. 


Fig.  9.  Fig.  10.  Fig.  11. 


Great  care  must  be  taken  to  hold  the  paper  invariably  in  the  same  posi- 
tion, since,  if  it  be  held  lower  down,  the  lower  border  of  the  black  zone 
will  move  higher  up. 

I prefer  to  read-off  in  a light  which  causes  the  appearance  represented 
in  fig.  9. 

By  the  use  of  Erdmann’s  float  * all  uncertainties  in  reading-off  may  be 
avoided.  Fig.  12  represents  a burette  thus  provided.  In  this  case  we 
always  read  off  the  degree  of  the  burette  which  coincides  with  the  circle 
in  the  middle  of  the  float.  The  float  must  be  so  fitted  to  the  width  of  the 
burette  that  when  placed  in  the  filled  burette,  it  will,  on  allowing  the 
fluid  to  run  out  gradually,  sink  down  with  the  same  without  wavering, 
and  when  it  has  been  pressed  down  into  the  fluid  of  the  closed  burette,  it 
will  slowly  rise  again.  The  weight  of  the  float  must,  if  necessary,  be  so 
regulated  by  mercury  that  when  placed  in  the  filled  tube  it  may  cut  the 
fluid  with  its  top  uniformly  all  round.  A further  important  condition 
of  the  float  is  that  its  axis  should  coincide  as  nearly  as  possible  with 
that  of  the  burette  tube,  so  that  the  division-mark  on  the  burette  may 
be  always  parallel  with  the  circular  line  on  the  float. 

The  correctness  of  the  graduation  of  a burette  is  tested  in  the  most 
simple  way,  as  follows : fill  the  instrument  up  to  the  highest  division 


* Journ.  f.  prakt.  Chem.  71,  194. 


30 


OPERATIONS. 


[§  22. 


■with  water  of  16°,  then  let  10  c.  c.  of  the  liquid  flow  out  into  an  accu- 
rately weighed  flask,  and  weigh;  then  let  another  quantity  of  10c.  c. 

flow  out,  and  weigh  again,  and  repeat  the  operation 
until  the  contents  of  the  burette  are  exhausted.  If 
the  instrument  is  correctly  graduated,  every  10  c.  c. 
of  water  of  16°  must  weigh  9’990  grm.  Differences 
up  to  O’OIO  grm.  may  be  disregarded,  since  even  with 
the  greatest  care  bestowed  on  the  process  of  reading- 
off,  deviations  to  that  extent  will  occur  in  repeated 
measurements  of  the  uppermost  10  c.  c.  of  one  and  the 
same  burette.  With  the  float-burettes  the  weighings 
agree  much  more  accurately,  and  the  differences  for 
10  c.  c.  do  not  exceed  0*002  grm. 

Mohr’s  burette  is  unquestionably  the  best  and  most 
convenient  instrument  of  the  kind,  and  ought  to  be 
employed  in  the  measurement  of  all  liquids  which  are 
not  injuriously  affected  by  contact  with  caoutchouc. 
Of  the  standard  solutions  used  at  present  in  volumetric 
analysis,  that  of  permanganate  of  potassa  alone  cannot 
bear  contact  with  caoutchouc. 

§ 22. 

II.  Gay-Lussac's  Burette, 

Fig.  13  represents  this  instrument  in, 
as  I believe,  its  most  practical  form. 

I make  use  of  two  sizes,  one  of  fifty  c. 
c.  divided  into  ^ c.  c.,  the  other  of  30  c. 

Fig.  12.  c.  divided  into  c.  c.  The  former  is 
about  33  cm.  long  ; the  graduated  por- 
tion occupies  about  25  cm. ; the  internal  diameter  of  the 
wide  tube  measures  15  mm. ; that  of  the  narrow  tube  4 
mm.,  which  in  the  upper  bent  end  gradually  decreases  to  2 
mm.  The  graduated  portion  of  the  smaller  burette  is 
about  28  cm.  long,  and  has  accordingly  an  internal  diameter 
of  about  11  mm. 

The  stand  which  I make  use  of  to  rest  my  burettes  in, 
consists  of  a disk  of  solid  wood,  from  5 to  6 cm.  high,  and 
from  10  to  12  cm.  in  diameter,  with  holes  made  with  the 
auger  and  chisel,  of  proper  size  to  receive  the  bottom  part  of 
the  burettes. 

To  complete  the  instrument,  Mohr  suggests  the  use  of  a 
perforated  cork,  bearing  a short  glass  tube  bent  at  a right 
angle.  The  cork  being  inserted  into  the  mouth  of  the  wide 
tube,  a piece  of  caoutchouc  is  drawn  over  the  short  glass 
tube ; by  blowing  into  this  with  greater  or  less  force,  the 
outflow  of  the  liquid  from  the  spout  of  the  slightly  slanting 
burette  may  be  regulated  at  pleasure. 

The  reading-off  of  the  height  of  the  liquid  is  effected  in 
the  same  way  as  explained  in  § 21.  I prefer,  however, 
placing  the  burette  firmly  against  a perpendicular  partition,  either  a 
strongly  illumined  door,  or  the  pane  of  a window,  to  insure  the  vertical 


Fig.  13. 


MEASURING  OF  FLUIDS. 


31 


S3  23> 2M 


position  of  the  instrument.  It  is  only  when  operating  with  more  highly 
concentrated,  and  accordingly  opaque  solutions  of  permanganate  of  potassa, 
that  the  method  of  reading  oft*  requires  modification ; in  that  case,  the 
upper  border  of  the  liquid  is  noted ; an4  the  best  way  is  to  place  the 
burette  against  a white  background,  and  read  off  by  reflected  light. 


§23. 

III.  Geissler’s  Burette. 

In  this  instrument,  which  is  represented  in  fig.  14,  the  narrow  tube 
is  placed  inside  the  wide  tube  instead  of  outside,  as  in  Gay-Lussac’s 
burette.  The  part  of  the  inner  tube  projecting  beyond  the  wide  tube  is 
thick  in  the  glass ; whilst  the  part  inside,  which  is  of  the  same  inside 
width,  is  made  of  very  thin  glass. 

This  is  a very  convenient  instrument,  and  less 
liable  to  fracture  than  Gay-Lussac’s  burette. 


II.  Preliminary  Operations. — Preparation  of 
Substances  for  the  Processes  of  Quantita- 
tive Analysis. 

§24. 

1.  The  Selection  of  the  Sample. 


Before  the  analyst  proceeds  to  make  the  quanti- 
tative analysis  of  a body,  he  cannot  too  carefully 
consider  whether  the  desired  result  is  fully  attained 
if  he  simply  knows  the  respective  quantity  of  every 
individual  constituent  of  that  body.  This  primary 
point  is  but  too  frequently  disregarded,  and  thus 
false  impressions  are  made,  even  by  the  most  care- 
ful analysis.  This  remark  applies  both  to  scientific 
and  to  technical  investigations. 

Therefore,  if  you  have  to  determine  the  constitu- 
tion of  a mineral,  take  the  greatest  possible  care  to 
remove  in  the  first  place  every  particle  of  gangue, 
and  disseminated  impurities  ; remove  any  adherent 
matter  by  wiping  or  washing,  then  wrap  the  sub- 
stance up  in  a sheet  of  thick  paper,  and  crush  it  to 
pieces  on  a steel  anvil ; and  pick  out  with  a pair  of 
small  pincers  the  cleanest  pieces.  Cry  stall  ine  sub- 
stances, prepared  artificially,  ought  to  be  purified 
by  recrystallization  ; precipitates  by  thorough  wash- 
ing, &c.,  &c. 

In  technical  investigations, — when  called  upon, 
for  instance,  to  determine  the  amount  of  peroxide 
present  in  a manganese  ore,  or  the  amount  of  iron 
present  in  an  iron  ore, — the  first  point  for  consider-  Fig.  14. 

ation  ought  to  be  whether  the  samples  selected  cor- 
respond as  much  as  possible  to  the  average  quality  of  the  ore.  What 


32 


OPERATIONS. 


L§  25. 

would  it  serve,  indeed,  to  tlie  purchaser  of  a manganese  mine  to  know  the 
amount  of  peroxide  present  in  a select,  possibly  particularly  rich,  sample  ? 

These  few  observations  will  suffice  to  show  that  no  universally  appli- 
cable and  valid  rules  to  guide  the  analyst  in  the  selection  of  the  sample 
can  be  laid  down ; he  must  in  every  individual  case,  on  the  one  hand, 
examine  the  substance  carefully,  and  more  particularly  also  under  the 
microscope,  or  through  a lens ; and,  on  the  other  hand,  keep  clearly  in 
view  the  object  of  the  investigation,  and  then  take  his  measures  accord- 
ingly. 


§ 25. 

2.  Mechanical  Division. 

In  order  to  prepare  a substance  for  analysis,  i.e .,  to  render  it  accessible 
to  the  action  of  solvents  or  fluxes,  it  is  generally  indispensable,  in  the 
first  place,  to  divide  it  into  minute  parts,  since  this  will  create  abun- 
dant points  of  contact  for  the  solvent,  and  will  counteract,  and,  as  far  as 
practicable,  remo  ve  the  adverse  influences  of  the  power  of  cohesion,  thus 
fulfilling  all  the  conditions  necessary  to  effect  a complete  and  speedy 
solution. 

The  means  employed  to  attain  this  object  vary  according  to  the  nature 
of  the  different  bodies  we  have  to  operate  upon.  In  many  cases,  simple 
crushing  or  pounding  is  sufficient ; in  other  cases  it  is  necessary  to  reduce 
the  powder  to  the  very  highest  degree  of  fineness,  by  sifting  or  by  elu- 
triation. 

The  operation  of  powdering  is  conducted  in  mortars ; the  first  and  most 
indispensable  condition  is,  that  the  material  of  the  mortar  be  considerably 
harder  than  the  substance  to  be  pulverized,  so  as  to  prevent,  as  far  as 
practicable,  the  latter  from  being  contaminated  with  any  particles  of  the 
former.  Thus,  for  pounding  salts  and  other  substances  possessing  no 
very  considerable  degree  of  hardness,  porcelain  mortars  may  be  used, 
whilst  the  pounding  of  harder  substances  (of  most  minerals,  for  instance,) 
requires  vessels  of  agate,  chalcedony,  or  flint.  In  such  cases,  the  larger 
pieces  are  first  reduced  to  a coarse  powder;  this  is  best  effected  by 
wrapping  them  up  in  several  sheets  of  writing-paper,  and  striking  them 

with  a hammer  upon  a steel  or  iron  plate ; 
the  coarse  powder  thus  obtained  is 
then  pulverized,  in  small  portions  at  a 
time,  in  an  agate  mortar,  until  it  is  re- 
duced to  the  state  of  an  impalpable  pow- 
der. If  we  have  but  a small  portion  of 
a mineral  to  operate  upon,  and  indeed  in 
all  cases  where  we  are  desirous  of  avoid- 
ing loss,  it  is  advisable  to  use  a steel 
mortar  (fig.  15)  for  the  preparatory  re- 
duction of  the  mineral  to  coarse  powder. 
a b and  c d represent  the  two  parts  of 
k the  mortar  ; these  may  be  readily  taken 
asunder.  The  substance  to  be  crushed 
(having,  if  practicable,  first  been  broken 
into  small  pieces),  is  placed  in  the  cy- 
lindrical chamber  efj  the  steel  cylinder, 


Fig.  15. 


which  fits  somewhat  loosely  into  the  chamber,  serves  as  pestle.  The 


25.] 


MECHANICAL  DIVISION. 


33 


mortar  is  placed  upon  a solid  support,  and  perpendicular  blows  are  re- 
peatedly struck  upon  the  pestle  with  a hammer  until  the  object  in  view 
is  attained. 

Minerals  which  are  very  difficult  to  pulverize  should  be  strongly 
ignited,  and  then  suddenly  plunged  into  cold  water,  and  subsequently 
again  ignited.  This  process  is  of  course  applicable  only  to  minerals 
which  lose  no  essential  constituent  on  ignition,  and  are  perfectly  insolu- 
ble in  water. 

In  the  purchase  of  agate  mortars,  especial  care  ought  to  be  taken 
that  they  have  no  palpable  cracks  or  indentations ; very  slight  cracks, 
however,  that  cannot  be  felt,  do  not  render  the  mortar  useless,  although 
they  impair  its  durability. 

Minerals  insoluble  in  acids,  and  which  consequently  require  fusing, 
must  especially  be  finely  divided,  otherwise  we  cannot  calculate  upon 
complete  decomposition.  This  object  may  be  obtained  either  by  tritu- 
rating the  pounded  mineral  with  water,  or  by  elutriation,  or  by  sifting ; 
the  two  former  processes,  however,  can  be  resorted  to  only  in  the  case 
of  substances  which  are  not  attacked  by  water.  It  is  quite  clear  that 
analysts  must  in  future  be  much  more  cautious  in  this  point  than  has 
hitherto  been  the  case,  since  we  know  now  that  many  substances  which 
are  usually  held  to  be  insoluble  in  water  are,  when  in  a state  of  minute 
division,  strongly  affected  by  that  solvent ; thus,  for  instance,  water, 
acting  upon  some  sorts  of  finely  pulverized  glass,  is  found  to  rapidly 
dissolve  from  2 to  3 per  cent,  of  the  powder  even  in  the  cold.  (Pelouze.*) 
Thus,  again,  finely  divided  feldspar,  granite,  trachyte  and  porphyry  give 
up  to  water  both  alkali  and  silica.  (H.  Ludwig. f) 

Trituration  ivith  water  (levigatioii).  Add  a little  water  to  the  pounded 
mineral  in  the  mortar,  and  triturate  the  paste  until  all  crepitation  ceases, 
or,  which  is  a more  expeditious  process,  transfer  the  mineral  paste  from 
the  mortar  to  an  agate  or  flint  slab,  and  triturate  it  thereon  with  a 
muller.  Rinse  the  paste  off,  with  the  washing  bottle,  into  a smooth 
porcelain  basin  of  hemispheric  form,  evaporate  the  water  on  the  water- 
bath,  and  mix  the  residue  most  carefully  with  the  pestle.  (The  paste 
may  be  dried  also  in  the  agate  mortar,  but  at  a very  gentle  heat,  since 
otherwise  the  mortar  might  crack.) 

To  perform  the  process  of  elutriation , the  pasty  mass,  having  first  been 
very  finely  triturated  with  water,  is  washed  off  into  a beaker,  and  stirred 
with  distilled  water ; the  mixture  is  then  allowed  to  stand  a minute  or 
so,  after  which  the  supernatant  turbid  fluid  is  poured  off  into  another 
beaker.  The  sediment,  which  contains  the  coarser  parts,  is  then  again 
subjected  to  the  process  of  trituration,  &c.,  and  the  same  operation  re- 
peated until  the  whole  quantity  is  elutriated.  The  turbid  fluid  is 
allowed  to  stand  at  rest  until  the  minute  particles  of  the  substance  held 
in  suspension  have  subsided,  which  generally  takes  many  hours.  The 
water  is  then  finally  decanted,  and  the  powder  dried  in  the  beaker. 

The  process  of  sifting  is  conducted  as  follows : a piece  of  fine,  well- 
washed,  and  thoroughly  dry  linen  is  placed  over  the  mouth  of  a bottle 
about  10  cm.  high,  and  pressed  down  a little  into  the  mouth,  so  as  to 
form  a kind  of  bag ; a portion  of  the  finely  triturated  substance  is  put 
into  the  bag,  and  a piece  of  soft  leather  stretched  tightly  over  the  top 


3 


* Compt.  Rend.  t.  xliii.,  pp.  117-123.. 
f Archiv  der  Pharm.  91,  147.. 


34 


OPERATIONS. 


[8  26- 

by  way  of  cover.  By  drumming  with  the  finger  on  the  leather  cover,  a 
shaking  motion  is  imparted  to  the  bag,  which  makes  the  finer  particles 
of  the  powder  gradually  pass  through  the  linen.  The  portion  remaining 
in  the  bag  is  subjected  again  to  trituration  in  an  agate  mortar,  and,  to- 
gether with  a fresh  portion  of  the  powder,  sifted  again ; and  the  same 
process  is  continued  until  the  entire  mass  has  passed  through  the  bag 
into  the  glass. 

When  operating  on  substances  consisting  of  different  compounds  it 
would  be  a grave  error  indeed  to  use  for  analysis  the  powder  resulting 
from  the  first  process  of  elutriation  or  sifting,  since  this  will  contain  the 
more  readily  pulverizable  constituents  in  a greater  proportion  to  the 
more  resisting  ones  than  is  the  case  with  the  original  substance. 

Great  care  must,  therefore,  also  be  taken  to  avoid  a loss  of  substance 
in  the  process  of  elutriation  or  sifting,  as  this  loss  is  likely  to  be  distri- 
buted unequally  among  the  several  component  parts. 

In  cases  where  it  is  intended  to  ascertain  the  average  composition  of 
a heterogeneous  substance,  of  an  iron  ore  for  instance,  a large  average 
sample  is  selected,  and  reduced  to  a coarse  powder ; the  latter  is 
thoroughly  intermixed,  a portion  of  it  powdered  more  finely,  and  mixed 
uniformly,  and  finally  the  quantity  required  for  analysis  is  reduced  to 
the  finest  powder.  The  most  convenient  instrument  for  the  crushing 
and  coarse  pounding  of  large  samples  of  ore,  &c.,  is  a steel  anvil  and 
hammer.  The  anvil  in  my  own  laboratory  consists  of  a wood  pillar,  85 
cm.  high  and  26  cm.  in  diameter,  into  which  a steel  plate,  3 cm.  thick 
and  20  cm.  in  diameter,  is  let  to  -the  depth  of  one-half  of  its  thickness. 
A brass  ring,  5 cm.  high,  fits  round  the  upper  projecting  part  of  the 
steel  plate.  The  hammer,  which  is  well  steeled,  has  a striking  surface 
of  5 cm.  diameter.  An  anvil  and  hammer  of  this  kind  afford,  among 
others,  this  advantage,  that  their  steel  surfaces  admit  most  readily  of 
cleaning.  To  convert  the  coarse  powder  into  a finer,  a smooth-turned 
steel  mortar  of  about  130  mm.  upper  diameter  and  74  mm.  deep  is  used 
— the  final  trituration  is  conducted  in  an  agate  mortar. 

§ 26. 

3.  Drying. 

Bodies  which  it  is  intended  to  analyze  quantitatively,  must  be,  when 
weighed,  in  a definite  state,  in  a condition  in  which  they  can  be  always 
obtained  again. 

Now,  the  essential  constituents  of  a substance  are  usually  accompanied 
by  an  unessential  one,  viz.,  a greater  or  less  amount  of  water,  enclosed 
either  within  its  lamellfe,  or  adhering  to  it  from  the  mode  of  its  prepara- 
tion, or  absorbed  by  it  from  the  atmosphere.  It  is  perfectly  obvious  that 
to  estimate  correctly  the  quantity  of  a substance,  we  must,  in  the  first 
place,  remove  this  variable  amount  of  water.  Most  solid  bodies , there- 
fore, require  to  be  dried  before  they  can  be  quantitatively  analyzed. 

The  operation  of  drying  is  of  the  very  highest  importance  for  the 
correctness  of  the  results  ; indeed  it  may  safely  be  averred  that  many  of 
the  differences  observed  in  analytical  researches  proceed  entirely  from 
the  fact  that  substances  are  analyzed  in  different  states  of  moisture. 

Many  bodies  contain,  as  is  well  known,  water  which  is  proper  to  them 
either  as  inherent  in  theii*  constitution  or  as  so-called  water  of  crystal- 


DESICCATION. 


35 


§27.] 

lization.  In  contradistinction  to  this,  we  will  employ  the  term  moisture 
to  designate  that  variable  adherent  or  mechanically  enclosed  water,  with 
the  removal  of  which  the  operation  of  drying  in  the  sense  here  in  view 
is  alone  concerned. 

In  the  drying  of  substances  for  quantitative  analysis,  our  object  is  to 
remove  all  moisture,  without  interfering  in  the  slightest  degree  with 
combined  water  or  any  other  constituent  of  the  body.  To  accomplish 
this  object,  it  is  absolutely  requisite  that  we  should  know  the  properties 
which  the  substance  under  examination  manifests  in  the  dry  state,  and 
whether  it  loses  water  or  other  constituents  at  a red  heat,  or  at  100°,. 
or  in  dried  air,  or  even  simply  in  contact  with  the  atmosphere.  These 
data  will  serve  to  guide  us  in  the  selection  of  the  process  of  desiccation 
best  suited  to  each  substance.* 

The  following  classification  may  accordingly  be  adopted  : — 

a . Substances  which  lose  water  even  in  simple  contact  with  the  atmo- 
sphere / such  as  sulphate  of  soda,  crystallized  carbonate  of  soda,  &c. 
Substances  of  this  kind  turn  dull  and  opaque  when  exposed  to  the  air, 
and  finally  crumble  wholly  or  partially  to  a white  powder.  They  are 
more  difficult  to  dry  than  many  other  bodies.  The  process  best  adapted 
for  the  purpose,  is  to  press  the  pulverized  salts  with  some  degree  of  force 
between  thick  layers  of  fine  white  blotting-paper,  repeating  the  operation 
with  fresh  paper  until  the  last  sheets  remain  absolutely  dry. 

It  is  generally  advisable  in  the  course  of  this  operation  to  repowder  the 
salt. 

b.  Substances  which  do  not  yield  water  to  the  atmosphere  ( unless  it  is 
perfectly  dry ),  but  effloresce  in  artificially  dried  air  / such  as  sulphate  of 
magnesia,  tartrate  of  potassa  and  soda  (Rochelle  salt),  &c.  Salts  of  this 
kind  are  reduced  to  powder,  which,  if  it  be  very  moist,  is  pressed  between 
sheets  of  blotting  paper,  as  in  a ; after  this  operation,  it  must  be  allowed 
to  remain  for  some  time  spread  in  a thin  layer  upon  a sheet  of  blotting- 
paper,  effectually  protected  against  dust,  and  shielded  from  the  direct 
rays  of  the  sun. 

§ 27. 

e.  Substances  which  undergo  no  alteration  in  dried  air , but  lose  water 
at  100° ; tartrate  of  lime,  for  instance.  These  are  finely  pulverized ; the 
powder  is  put  in  a thin  layer  into  a watch-glass  or  shallow  dish,  and  the 
latter  placed  inside  a chamber  in  which  the  air  is  kept  dry  by  means  of 
sulphuric  acid.  This  process  is  usually  conducted  in  one  of  the  following 
apparatuses,  which  are  termed  desiccators , and  Subserve  still  another 
purpose  besides  that  of  drying,  viz.,  that  of  allowing  hot  crucibles,  dishes, 
&c.,  to  cool  in  dry  air. 

In  fig.  16,  a represents  a glass  plate  (ground-glass  plates  answer  the 
purpose  best),  5,  a bell  jar  with  ground  rim,  which  is  greased  with 
tallow ; c is  a glass  basin  with  sulphuric  acid ; <i,  a round  iron  plate, 
supported  on  three  feet,  with  circular  holes  of  various  sizes,  for  the 
reception  of  the  watch-glasses,  crucibles,  &c.,  containing  the  substance. 

* The  dried  substance  should  always  at  once  be  transferred  to  a well-closed 
vessel ; glass  tubes,  sealed  at  one  end,  and  of  sufficiently  thick  ‘glass  to  bear  the 
firm  insertion  of  tight-fitting  smooth  corks — weighing-tubes — are  usually  em- 
ployed for  this  purpose. 


36 


OPERATIONS. 


[§  28. 


In  fig.  1 7,  a represents  a beaker  with  ground  and  greased  rim,  and 
filled  to  one-fourth  or  one-third  with  concentrated  sulphuric  acid  ; b is 
a ground-glass  plate ; c is  a bent  wire  of  lead,  which  serves  to  support 
the  watch-glass  containing  the  substance. 


Fig.  18  represents  a readily  portable  desiccator,  used  more  particularly 
to  receive  crucibles  in  course  of  cooling,  and  carry  them  to  the  balance. 

The  instrument  consists  of  a box  made  of 
strong  glass ; the  lid  must  be  ground  to 
shut  air-tight ; the  place  on  which  it  joins  is 
greased  with  tallow.  The  outer  diameter 
of  my  boxes  is  105  mm. ; the  sides  are  6 
mm.  thick.  The  aperture  has  a diameter 
of  80  mm. ; the  box  up  to  the  small  part  is 
65  mm.  high ; the  lid  has  the  same  height ; 
the  small  part  itself  is  15  mm.  high,  and 
ground  to  a slightly  conical  shape.  A 
brass  ring,  with  rim,  fits  exactly  into  the 
aperture  ; the  rim  must  not  project  beyond 
the  glass.  The  ring  bears  a triangle  of 
iron,  or,  better,  platinum  wire,  intended 
for  the  reception  of  crucibles,  &c. 

The  body  which  it  is  intended  to  dry 
is  kept  exposed  to  the  action  of  the  dry 
air  in  the  glass,  until  it  shows  no  further 
diminution  of  weight.  Substances  upon 
which  the  oxygen  of  the  air  exercises  a 
modifying  influence  are  dried  in  a simi- 
lar manner,  under  the  exhausted  receiver 
of  an  air-pump.  Substances  which,  though  losing  no  water  in  dry  air, 
yet  give  off  ammonia,  are  dried  over  quicklime,  mixed  with  some  chlo- 
ride of  ammonium  in  powder,  and  consequently  in  an  anhydrous  am* 
moniacal  atmosphere. 


§ 28. 

d.  Substances  which  at  100°  completely  lose  their  moisture , without  suf- 
fering any  other  alteration , such  as  bitartrate  of  potassa,  sugar,  &c. 
These  are  dried  in  the  water-bath  ; in  the  case  of  slow-drying  substances, 


DESICCATION-. 


37 


§28.1 

or  where  it  is  wished  to  expedite  the  operation,  with  the  aid  of  a cur- 
rent of  dry  air. 

Fig.  19  represents  the  water-bath  most 
commonly  used.  It  is  made  of  sheet  cop- 
per. The  engraving  renders  a detailed  de- 
scription unnecessary.  The  inner  cham- 
ber, c,  is  surrounded  on  five  sides  by  the 
outer  case  or  jacket,  d e,  without  commu- 
nicating with  it.  The  object  of  the  aper- 
tures g and  h is  to  effect  change  of  air, 
which  purpose  they  answer  sufficiently  well. 

When  it  is  intended  to  use  the  apparatus, 
the  outer  case  is  filled  to  about  one-half  with  rain-water,  and  the 
aperture  a is  closed  with  a perforated  cork,  into  which  a glass  tube 
is  fitted ; the  aperture  b is  entirely  closed.  If  the  apparatus  is  intended 
to  be  heated  over  charcoal,  it  should  have  a length  of  about  20  cm. 
from  d to  but  if  over  a gas-,  spirit-,  or  oil-lamp,  it  should  be  only  about 

13  cm.  long.  In  the  former  case,  the  inner  chamber  is  17  cm.  deep, 

14  cm.  broad,  and  10  cm.  high  ; in  the  latter  case,  it  is  10  cm.  deep,  9 
cm.  broad,  and  6 cm.  high.  The  temperature  in  the  inner  chamber 
never  quite  reaches  100°  ; to  bring  it  up  to  100°,  F.  Rochleder  has 
suggested  to  close  b with  a double-limbed  tube,  the  outer  longer  limb 
of  which  dips  into  a cylinder  filled  with  water;  a is  in  that  case  closed 
with  a perforated  cork  bearing  a sufficiently  tall  funnel  tube,  which  fits 
air-tight  in  the  cork.  The  lower  end  of  this  tube  reaches  down  to  one 
inch  from  the  bottom. 

In  large  analytical  laboratories  water  is  usually  kept  boiling  all  day 
long,  for  the  production  of  distilled  water.  The  boilers  used  in  my  own 
laboratory  have  the  shape  of  somewhat  oblong  square  boxes,  about 
120  cm.  long,  60  cm.  broad,  and  24  cm.  high;  the  front  of  the  boiler 
has  soldered  into  it,  one  above  the  other,  two  rows  of  drying  cham- 
bers, of  the  kind  shown  in  fig.  19.  This  gives  so  many  ovens  that 
almost  every  student  may  have  one  for  his  special  use.  Most  of 
these  ovens  are  from  11  to  12  cm.  deep  and  broad,  and  8 cm.  high ; 
some  of  them,  however,  are  16  cm.  deep  and  broad,  to  enable  them  to 
receive  large-sized  dishes.  The  substances  to  be  dried  are  usually  put 
on  double  watch-glasses,  laid  one  within  the  other,  which  are  placed  in 
the  oven,  and  the  door  is  then  closed.  In  the  subsequent  process  of  weigh- 
ing, the  upper  glass,  which  contains  the  substance,  is  covered  with  the 
lower  one.  The  glasses  must  be  quite  cold  before  they  are  placed  on  the 
scale.  In  cases  where  we  have  to  deal  with  hygroscopic  substances,  the 
reabsorption  of  water  upon  cooling  is  prevented  by  the  selection  of  close- 
fitting  glasses,  which  are  held  tight  together  by  a clasp  (fig.  20),  and 
allowed  to  cool  with  their  contents 
under  a bell-glass  over  sulphuric  acid 
(see  fig.  16).  These  latter  instruc- 
tions apply  equally  to  the  process  of 
drying  conducted  in  other  apparatus. 

The  clasp  used  for  keeping  the 
watch-glasses  pressed  together — and  Fig.  20. 

which  in  all  cases  where  it  is  intended 

to  ascertain  the  loss  of  weight  which  a substance  suffers  on  desiccation,  is 
to  be  looked  upon  as  belonging  to  the  glasses,  and  must  accordingly  be 


Fig.  19. 


38 


OPERATIONS. 


[§  29. 

weighed  with  them — is  constructed  of  two  strips  of  thin  brass  plate,  about 
10  cm.  long,  and  1 cm.  wide,  which  are  laid  the  one  over  tho  other,  and 
soldered  together  at  the  ends,  to  the  extent  of  5 to  6 mm. 

The  following  apparatus  (fig.  21)  serves  for  drying  substances  in  a 
current  of  air  : — 


Fig.  21. 


a represents  a flask  filled  to  one-third  with  concentrated  sulphuric 
acid ; c a glass  vessel  (commonly  called  a Liebig’s  drying-tube),  and  d a tin 
vessel,  provided  with  a stop-cock  at  e,  and  arranged  in  other  respects  as 
the  cut  shows. 

A,  i,  represents  a small  tin  vessel,  containing  water  and  covered  with 
a lid ; two  apertures  are  cut  into  the  border  of  the  latter,  to  receive 
the  ascending  limbs  of  c. 

The  tube  c is  first  weighed  with  the  substance,  then  placed  in  the  water- 
bath,  A,  i,  which  is  placed  over  a spirit-  or  gas-lamp ; the  aspirator 
d is  then  filled  with  water,  and  c connected  with  the  flask  a by  the  per- 
forated cork  gy  and  with  d by  means  of  a caoutchouc  tube  f.  If  the 
stop-cock  e be  now  opened  so  as  to  cause  the  water  to  drop  from  d,  the 
air  will  pass  through  the  tube  b , and  after  being  dehydrated  by  the  sul- 
phuric acid,  will  pass  over  the  heated  substance  in  c.  After  the  operation 
has  been  continued  for  some  time,  it  is  interrupted  for  the  purpose  of 
weighing  the  tube  c and  its  contents,  and  then  resumed  again,  and  con- 
tinued until  the  weight  of  c (and  its  contents)  remains  stationary.  The 
current  of  cold  air,  exercising  its  constant  cooling  action  upon  the  sub- 
stance, the  latter  never  really  reaches  100°.  It  is,  therefore,  sometimes 
advisable  to  substitute  for  the  water  in  the  bath  a saturated  solution  of 
common  salt. 

With  this  substitution,  the  apparatus  represented  in  fig.  21  will  be 
found  to  effect  its  purpose  the  most  expeditiously.  It  is  not  adapted, 
however,  for  drying  such  substances  as  have  a tendency  to  fuse  or  agglu- 


e.  Substances  which  persistently  retain  moisture  at  100°,  or  become  com- 
pletely dry  only  after  a very  long  time  y but  which  are  decomposed  by  a 
red  heat . 

The  desiccation  of  such  substances  is  effected  in  the  air-bath  or  oil- 
bath,  the  temperature  being  raised  to  110—120°,  and  still  higher,  and, 


DESICCATION. 


39 


§29.] 


according  to  circumstances,  with  or  without  application  of  a current  of 
air,  carbonic  acid,  or  hydrogen. 

Figs.  22  and  23  represent  two  air-baths  of  simple  construction  ; the  for- 
mer (fig.  22)  adapted  for  the  desiccation  of  a single  substance,  the  latter 
suited  for  the  simultaneous  drying  of  several  substances. 

In  fig.  22,  A is  a box  of  strong  sheet  copper,  about 
1 1 cm.  high,  and  9 cm.  in  diameter.  The  box  is  closed 
with  the  loose-fitting  cover  JJ,  which  is  provided  with 
a narrow  rim,  and  has  two  apertures,  G and  E j C is 
intended  to  receive  the  thermometer  J9,  which  is  fitted 
into  it  by  a perforated  cork,  E affords  an  exit  to  the 
aqueous  vapors,  and  is,  according  to  circumstances, 
either  left  open,  or  loosely  closed.  In  the  interior  of 
the  box,  about  half-way  up,  are  fixed  three  pins,  sup- 
porting a triangle  of  moderately  stout  wire,  upon 
which  the  crucible  with  the  substance  is  placed  un- 
covered. The  bulb  of  the  thermometer  approaches  the 
crucible  as  closely  as  possible,  but  without  touching 
the  triangle.  The  heating  is  effected  by  means  of  a 
gas-  or  spirit-lamp.  When  the  apparatus  has  cooled 
sufficiently  to  allow  its  being  laid  hold  of  without  incon- 
venience, the  lid  is  removed,  the  crucible,  which  is  still 
warm,  taken  out,  covered,  and  allowed  to  cool  in  a desiccator ; and  weigh- 
ed when  cold. 

In  fig.  23,  a b is  a case  of  strong  sheet  copper,  with  riveted  or  lock- 
ed joints,  of  a width  and  depth  of 
15  to  20  cm.,  and  corresponding 
height.  The  aperture  c is  intend- 
ed to  receive  a perforated  cork, 
into  which  is  fixed  a thermometer, 
df  which  reaches  into  the  interior 
of  the  case  ; within  is  a shelf,  on 
which  are  placed  the  watch-glasses 
with  the  substances  to  be  dried. 

The  case  is  heated  by  means  of  a 
gas-,  spirit-,  or  oil-lamp.  When  the 
temperature  has  once  reached  the 
intended  point,  it  is  easy  to  main- 
tain it  pretty  constant,  by  regu- 
lating the  flame.*  In  order  to  limit 
as  much  as  possible  the  cooling 
from  without,  it  is  advisable  to  put 
over  the  whole  apparatus  a paste- 
board hood  with  a movable  front. 

[The  air-bath,  fig.  23,  by  a slight 
alteration,  may  serve  for  desicca- 
ting in  a stream  of  dry  air.  For  this  purpose,  cut  a circular  orifice,  35  mm. 
wide,  in  each  end  of  the  copper  chamber,  and  rivet  over  each  orifice  a cop- 
per tube  or  ring  of  corresponding  diameter,  and  25  mm.  long.  Fit  a glass 
tube  of  20  mm.  diameter,  by  means  of  perforated  corks,  into  these  open- 


* With  a gas-lamp,  Kemp’s  regulator  improved  by  Bunsen,  may  advantageously 
be  used  to  obtain  constant  temperatures. 


40 


OPERATIONS. 


ings,  so  that  it  shall  traverse  the  chamber  and  project  40-50  mm. 
beyond  the  corks  at  each  end.  The  copper  tubes  should  be  so  adjusted 
that  the  glass  tube  shall  stand  horizontally  in  the  chamber,  at  the  same 
height  as  the  thermometer  bulb  and  just  behind  it.  To  produce  the  cur- 
rent of  dry  air  one  of  the  projecting  ends  of  the  wide  tube  is  connected  by 
a narrow  glass  tube  and  perforated  cork,  with  an  aspirator  as  in  fig.  21,  the 
other  with  a large  chloride  of  calcium  tube  ; the  water  of  the  aspirator  is 
allowed  to  run  off  somewhat  rapidly  at  first,  more  slowly  afterwards. 
The  end  of  the  tube  that  delivers  the  air  into  the  wide  tube  is  recurved, 
so  that  the  substance  within  shall  not  be  carried  away  in  the  current. 


Fig.  24. 


The  substance  to  be  dried  is  weighed  out  in  a tray  of  platinum  or 
porcelain,  fig.  24,  which  is  pushed  within  the  wide  glass  tube  by  help  of 
a wire.  When  the  substance  is  hygroscopic,  the  tray  is  placed  horizon- 
tally within  a test-tube,  which  is  corked  while  the  weight  is  being  ascer- 
tained. The  substance  and  tray,  after  drying,  may  be  cooled  in  the  same 
test-tube  ; in  that  case,  just  before  putting  on  the  balance,  the  cork  should 
be  removed  momentarily  to  allow  the  tube  to  fill  with  air.] 

§ 30- 

The  copper  apparatus  represented  in  fig.  19,  when  made  with  brazed 
joints,  can  be  employed  also  as  a paraffine-bath;  when  used  for  that 
purpose,  the  outer  case  is  filled  to  two-thirds  with  paraffine.  To  note 
the  temperature,  a thermometer  is  inserted,  by  means  of  a perforated 
cork,  in  the  aperture  a ; with  the  bulb  reaching  nearly  to  the  bottom, 
or,  at  all  events,  entirely  immersed  in  the  paraffine. 

Many  organic  substances,  when  dried  at  a somewhat  high  temperature, 
suffer  alteration  by  the  action  of  the  atmospheric  oxygen.  In  the  desic- 
cation of  such  substances,  oxygen  must  accordingly  be  excluded. 

[The  drying  of  such  bodies  is  conducted  as  just  described  in  the  modified 
air-bath,  but  in  a stream  of  dried  and  purified  hydrogen  or  carbonic  acid 
(see  §29).  The  gas  is  evolved  from  a self-regulating  generator  (see  fig.  47, 
§ 108,  or  “ Qual.  Anal.,”  Am.  ed.  p.  49).  To  the  end  of  the  wide  tube  from 
which  the  gas  escapes  is  fitted  a perforated  cork  and  long  narrow  tube.] 

§ 81. 

f.  Substances  which  suffer  no  alteration  at  a red  heat , such  as  sulphate 
of  baryta,  pearlash,  &c.,  are  very  readily  freed  from  moisture.  They 
need  simply  be  heated  in  a platinum  or  porcelain  crucible  over  a gas  or 
spirit-lamp  until  the  desired  end  is  attained.  The  crucible,  having  first 
been  allowed  to  cool  a little,  is  put,  still  hot,  under  a desiccator,  and 
finally  weighed  when  cold. 

III.  General  Procedure  in  Quantitative  Analyses. 

§ 32. 

It  is  important,  in  the  first  place,  to  observe  that  we  embrace  in  the 
following  general  analytical  method  only  the  separation  and  determina- 
tion of  the  metals  and  their  combinations  with  the  metalloids,  and  of 
the  inorganic  acids  and  salts.  With  respect  to  the  quantitative  analysis 


DESICCATION. 


41 


§33.] 

of  other  compounds,  it  is  not  easy  to  lay  down  a universally  applicable 
method,  except  that  their  constituents  usually  require  to  be  converted, 
first  into  acids  or  bases,  before  their  separation  and  estimation  can  be 
attempted ; this  is  the  case,  for  instance,  with  sulphide  of  phosphorus* 
chloride  of  sulphur,  chloride  of  iodine,  sulphide  of  nitrogen,  &c. 

The  quantitative  analysis  of  a substance  presupposes  an  accurate 
knowledge  of  the  properties  of  the  same,  and  of  the  nature  of  its  several 
constituents.  These  data  will  enable  the  operator  at  once  to  decide 
whether  the  direct  estimation  of  each  individual  constituent  is  necessary ; 
whether  he  need  operate  only  on  one  portion  of  the  substance,  or 
whether  it  would  be  advantageous  to  determine  each  constituent  in 
different  portions.  Let  us  suppose,  for  instance,  we  have  a mixture  of 
chloride  of  sodium  and  anhydrous  sulphate  of  soda,  and  wish  to  ascertain 
the  proportion  in  which  these  two  substances  are  mixed.  Here  it 
would  be  superfluous  to  determine  each  constituent  directly,  since  the 
determination  either  of  the  quantity  of  the  chlorine,  or  of  the  sulphuric 
acid,  is  quite  sufficient  to  answer  the  purpose;  still  the  estimation  of 
both  the  chlorine  and  the  sulphuric  acid  will  afford  us  an  infallible  con- 
trol for  the  correctness  of  our  analysis ; since  the  united  weights  of  these 
two  substances,  added  to  the  sodium  and  soda  respectively  equivalent  to 
them,  must  be  equal  to  the  weight  of  the  substance  taken. 

These  estimations  may  be  made,  either  in  one  and  the  same  portion  of 
the  mixture,  by  first  precipitating  the  sulphuric  acid  with  nitrate  of 
baryta,  and  subsequently  the  hydrochloric  acid  from  the  filtrate  with 
solution  of  nitrate  of  silver ; or  a separate  portion  of  the  mixture  may 
be  appropriated  to  each  of  these  two  operations. » Unless  there  is  some 
objection  to  its  use  ( e.g .,  deficiency  or  heterogeneousness  of  substance), 
the  latter  method  is  more  convenient  and  generally  yields  more  accu- 
rate results  ; since,  in  the  former  method,  the  unavoidable  washing  of 
the  first  precipitate  swells  the  amount  of  liquid  so  considerably  that  the 
analysis  is  thereby  delayed,  and,  moreover,  loss  of  substance  less  easily 
guarded  against. 

Before  beginning  all  analyses,  at  least  those  of  a more  complex  nature, 
the  student  should  write  out  an  exact  plan,  and  accurately  note  on 
paper,  during  the  entire  process,  everything  that  he  does.  It  is  in  tho 
highest  degree  unwise  to  rely  on  the  memory  in  a complicated  analysis. 
When  students,  who  imagine  they  can  do  so,  come,  a week  or  a fort- 
night after  they  have  begun  their  analysis,  to  work  out  the  results, 
they  find  generally  too  late  that  they  have  forgotten  much,  which  now 
appears  to  them  of  importance  to  know.  The  intelligent  pursuit  of 
chemical  analysis  consists  in  the  projecting  and  accurate  testing  of  the 
plan ; acuteness  and  the  power  of  passing  in  review  all  the  influencing 
chemical  relations  must  here  support  each  other.  He  who  works  with- 
out a thoroughly  thought-out  plan,  has  no  right  to  say  he  is  practising 
chemistry ; for  a mere  unthinking  stringing  together  of  a series  of  fil- 
trations,  evaporations,  ignitions,  and  weighings,  howsoever  well  these 
several  operations  may  be  performed,  is  not  chemistry. 

We  will  now  proceed  to  describe  the  various  operations  constituting 
the  process  of  quantitative  analysis. 

§ 33. 

1.  Weighing  the  Substance. 

The  amount  of  matter  required  for  the  quantitative  analysis  of  a 


42 


OPERATIONS. 


[§  34. 

substance  depends  upon  the  nature  of  its  constituents  ; it  is,  therefore, 
impossible  to  lay  down  rules  for  guidance  on  this  point.  Half  a 
gramme  of  chloride  of  sodium,  and  even  less,  is  sufficient  to  effect  the 
estimation  of  the  chlorine.  For  the  quantitative  analysis  of  a mixture 
of  common  salt  and  anhydrous  sulphate  of  soda,  1 gramme  will  suffice ; 
whereas,  in  the  case  of  ashes  of  plants,  complex  minerals,  &c.,  3 or  4 
grammes,  and  even  more,  are  required.  1 to  3 grm.  can  therefore  be 
indicated  as  the  average  quantity  suitable  in  most  cases.  For  the  esti- 
mation of  constituents  present  in  very  minute  proportions  only,  as, 
for  instance,  alkalies  in  limestones,  phosphorus  or  sulphur  in  cast-iron, 
<fcc.,  much  greater  quantities  are  often  required — 10,  20,  or  50  grammes. 

The  greater  the  amount  of  substance  taken  the  more  accurate  will  be 
the  analysis ; the  smaller  the  quantity,  the  sooner,  as  a rule,  will  the 
analysis  be  finished.  We  would  advise  the  student  to  endeavor  to 
combine  accuracy  with  economy  of  time.  The  less  substance  he  takes 
to  operate  upon,  the  more  carefully  he  ought  to  weigh ; the  larger  the 
amount  of  substance,  the  less  harm  can  result  from  slight  inaccuracies  in 
weighing.  Somewhat  large  quantities  of  substance  are  generally 
weighed  to  1 milligramme ; minute  quantities,  to  of  a milligramme. 

If  one  portion  of  a substance  is  to  be  weighed  off,  we  first  weigh  two 
watch-glasses  which  fit  on  each  other,  or  else  an  empty  platinum  cruci- 
ble with  lid,  then  we  put  some  substance  in,  and  weigh  again ; the  differ- 
ence between  the  two  weighings  gives  the  weight  of  the  substance  taken. 

If  several  quantities  of  a substance  are  to  be  operated  upon,  the  best 
way  is  to  weigh  off  the  several  portions  successively  ; which  may  be 
accomplished  most  readily  by  weighing  in  a glass  tube,  or  other  appro- 
priate vessel,  the  whole  amount  of  substance,  and  then  shaking  out  of  the 
tube  the  quantities  required  one  after  another  into  appropriate  vessels, 
weighing  the  tube  after  each  time. 

The  work  may  often  also  be  materially  lightened,  by  weighing  off  a 
larger  portion  of  the  substance,  dissolving  this  to  y,  y or  1 litre,  and  tak- 
ing out  for  the  several  estimations  aliquot  parts,  with  the  50  or  100  c.  c. 
pipette.  The  first  ana  most  essential  condition  of  this  proceeding,  of 
course,  is  that  the  pipettes  must  accurately  correspond  with  the  measur- 
ing flasks  (§§  18  and  20). 

§ 34. 

2.  Estimation  of  the  Water. 

If  the  substance  to  be  examined — after  having  been  freed  from  mois- 
ture by  a suitable  drying  process  (§§  26 — 32) — contains  water,  it  is 
usual  to  begin  by  determining  the  amount  of  this  water.  This  operation 
is  generally  simple;  in  some  instances,  however,  it  has  its  difficulties. 
This  depends  upon  various  circumstances,  viz.,  whether  the  compounds 
intended  for  analysis  yield  their  water  readily  or  not ; whether  they  can 
bear  a red  heat  without  suffering  decomposition ; or  whether,  on  the 
contrary,  they  give  off  other  volatile  substances,  besides  water,  even  at 
a lower  temperature. 

The  correct  knowledge  of  the  constitution  of  a compound  depends 
frequently  upon  the  accurate  estimation  of  the  water  contained  in  it ; in 
many  cases — for  instance,  in  the  analysis  of  the  salts  of  known  acids — 
the  estimation  of  the  water  contained  in  the  analyzed  compound  suffices 
to  enable  us  to  deduc,e  the  formula.  The  estimation  ?f  the  water  com 


ESTIMATION  OF  WATER. 


43 


§3o.] 

tained  in  a substance  is,  therefore,  one  of  the  most  important,  as  well  as 
most  frequently  occurring  operations  of  quantitative  analysis.  The  pro- 
portion of  water  contained  in  a substance  may  be  determined  in  two 
ways,  viz.,  a,  from  the  diminution  of  weight  consequent  upon  the  expul- 
sion of  the  water ; b,  by  weighing  the  amount  of  water  expelled. 

§ 35. 

a.  Estimation  of  the  Water  from  the  Loss  of  Weight. 

This  method,  on  account  of  its  simplicity,  is  most  frequently  employed. 
The  modus  operandi  depends  upon  the  nature  of  the  substance  under 
examination. 

a.  The  Substance  bears  ignition  without  losing  other  Constituents  besides 
Water,  and  without  absorbing  Oxygen. 

The  substance  is  weighed  in  a platinum  or  porcelain  crucible,  and 
placed  over  the  gas  or  spirit  lamp ; the  heat  should  be  very  gentle  at 
first,  and  gradually  increased.  When  the  crucible  has  been  maintained 
some  time  at  a red  heat,  it  is  allowed  to  cool  a little,  put  still  warm 
under  the  desiccator,  and  finally  weighed  when  cold.  The  ignition  is 
then  repeated,  and  the  weight  again  ascertained.  If  no  further  diminu- 
tion of  weight  has  taken  place,  the  process  is  at  an  end,  the  desired  ob- 
ject being  fully  attained.  But  if  the  weight  is  less  than  after  the  first 
heating,  the  operation  must  be  repeated  until  the  weight  remains  constant. 

In  the  case  of  silicates,  the  heat  must  be  raised  to  a very  high  degree, 
since  many  of  them  ( e.g . talc,  steatite,  nephrite)  only  begin  at  a red  heat 
to  give  off  water,  and  require  a yellow  heat  for  the  complete  expulsion 
of  that  constituent.  (Th.  Scheerer.*)  Such  bodies  are  therefore 
ignited  over  a blast  lamp. 

In  the  case  of  substances  that  have  a tendency  to  puff  off,  or  to  spirt, 
a small  flask  or  retort  may  sometimes  be  advantageously  substituted  for 
the  crucible.  Care  must  be  taken  to  remove  the  last  traces  of  aqueous 
vapor  from  the  vessel,  by  suction  through  a glass  tube. 

Decrepitating  salts  (chloride  of  sodium,  for  instance)  are  put — finely 
pulverized,  if  possible — in  a small  covered  platinum  crucible,  which  is 
then  placed  in  a large  one,  also  covered ; the  whole  is  weighed,  then 
heated,  gently  at  first  for  some  time,  then  more  strongly  ; finally,  after 
cooling,  weighed  again. 

(3.  The  substance  loses  on  ignition  other  Constituents  besides  Water 
(JBoracic  Acid , Sulphuric  Acid , Fluoride  of  Silicon , dtc.). 

Here  the  analyst  has  to  consider,  in  the  first  place,  whether  the  water 
may  not  be  expelled  at  a lower  degree  of  heat,  which  does  not  involve 
the  loss  of  other  constituents.  If  this  may  be  done,  the  substance  is 
heated  either  in  the  water-bath,  or  where  a higher  temperature  is  re- 
quired, in  the  air-bath  or  oil-bath,  the  temperature  being  regulated  by 
the  thermometer.  The  expulsion  of  the  water  may  be  promoted  by 
the  co-operation  of  a current  of  air  (compare  §§29  and  30)  ; or  by  the 
addition  of  pure  dry  sand  to  the  substance,  to  keep  it  porous,  f The 

* Jahresber.  von  Liebig-  u.  Kopp,  1851,  610. 
f Ann.  d.  Chem.  u.  Pharm. , 53,  233. 


44  OPERATIONS.  [§  36. 

process  must  be  continued  under  these  circumstances  also,  until  the  weight 
remains  constant. 

In  cases  where,  for  some  reason  or  other,  such  gentle  heating  is  insuf- 
ficient, the  analyst  has  to  consider  whether  the  desired  end  may  not  be 
attained  at  a red  heat,  by  adding  some  substance  that  will  retain  the 
volatile  constituent  whose  loss  is  apprehended.  Thus,  for  instance,  the 
crystallized  sulphate  of  alumina  loses  at  a red  heat,  besides  water,  also 
sulphuric  acid ; now,  the  loss  of  the  latter  constituent  may  be  guarded 
against  by  adding  to  the  sulphate  an  excess  (about  six  times  the  quan- 
tity) of  finely  pulverized,  recently  ignited,  pure  oxide  of  lead.  But  the 
addition  of  this  substance  will  not  prevent  the  escape  of  fluoride  of 
silicon  from  silicates  when  exposed  to  a red  heat  (List  *). 

Thus  again,  the  amount  of  water  in  commercial  iodine  may  be  deter- 
mined by  triturating  the  iodine  together  with  eight  times  the  quantity 
of  mercury,  and  drying  the  mixture  at  100°  (BoLLEYf). 

y.  The  Substance  contains  several  differently  combined  quantities  of 
Water  which  require  different  Degrees  of  Temperature  for  Expulsion. 

Substances  of  this  nature  are  heated  first  in  the  water-bath,  until  their 
weight  remains  constant ; they  are  then  exposed  in  the  oil-  or  air-bath 
to  150,  200,  or  250°,  &c.,  and  finally,  when  practicable,  ignited  over  a 
gas-  or  spirit-lamp.  [In  such  experiments,  it  is  best  to  proceed  as  de- 
scribed, § 29,  p.  39,  viz.,  to  heat  in  a current  of  dried  air,  hydrogen,  or  car- 
bonic acid.] 

In  this  manner  differently  combined  quantities  of  water  may  be  dis- 
tinguished, and  their  respective  amounts  correctly  estimated.  Thus,  for 
instance,  crystallized  sulphate  of  copper  contains  28*87  per  cent,  of  water, 
which  escapes  at  a temperature  below  140°,  and  7*22  per  cent.,  which 
escapes  only  at  a temperature  between  220  and  260°. 

6.  When  the  substance  has  a tendency  to  absorb  oxygen  (from  the  pre- 
sence of  protoxide  of  iron,  for  instance)  the  water  is  better  determined 
in  the  direct  way,  than  by  the  loss.  (§  36.) 


§ 36. 

b.  Estimation  of  Water  by  Direct  Weighing. 

This  method  is  resorted  to  by  way  of  control,  or  in  the  case  of  substances 
which,  upon  ignition,  lose,  besides  water,  other  constituents,  which  cannot 
be  retained  even  by  the  addition  of  some  other  substance  ( e.g .,  carbonic 
acid,  oxygen),  or  in  the  case  of  substances  containing  bodies  inclined  to 
oxidation  ( e.g .,  protoxide  of  iron).  The  principle  of  the  method  is  to  expel 
the  water  by  the  application  of  a red  heat,  so  as  to  admit  of  the  condensa- 
tion of  the  aqueous  vapor,  and  the  collection  of  the  condensed  water  in 
an  appropriate  apparatus,  partly  physically,  partly  by  the  agency  of  some 
hygroscopic  substance.  The  increase  in  the  weight  of  this  apparatus 
represents  the  quantity  of  the  water  expelled. 

The  operation  may  be  conducted  in  various  ways ; the  following  is  one 
of  the  most  appropriate  : — 


* Arm,  d.  Chem.  u.  Pharm.,  81,  189. 


f Dingler’s  Polyt.  Joum.,  126,  39. 


ESTIMATION  OF  WATER. 


45 


§36.] 


J?,  fig.  25,  represents  a gasometer  filled  with  air ; b a flask  half-filled 
with  concentrated  sulphuric  acid  ; c and  a o are  chloride  of  calcium  tubes  ; 
d is  a bulb-tube. 


The  substance  intended  for  examination  is  weighed  in  the  perfectly  dry 
tube  d*  which  is  then  connected  with  c and  the  weighed  chloride  of  cal- 
cium tube  a o , by  means  of  sound  and  well-dried  perforated  corks. 

The  operation  is  commenced  by  opening  the  stop-cock  e a little,  to 
allow  the  air,  which  loses  all  its  moisture  in  b and  c,  to  pass  slowly  through 
d ; the  tube  d is  then  heated  to  beyond  the  boiling-point  of  water,  by  hold- 
ing a lamp  towards  /,  taking  care  not  to  burn  the  cork ; and  finally,  the 
bulb  which  contains  the  substance  is  exposed  to  a low  red  heat,  the  tem- 
perature at  / being  maintained  all  the  while  at  the  point  indicated. 
When  the  expulsion  of  the  water  has  been  accomplished,  a slow  current  of 
air  is  still  kept  up  till  the  bulb-tube  is  cold  ; the  apparatus  is  then  dis- 
connected, and  the  chloride  of  calcium  tube  a o,  weighed.  The  increase 
in  the  weight  of  this  tube  represents  the  quantity  of  water  originally 
present  in  the  substance  examined. 

The  empty  bulb  a , in  which  the  greater  portion  of  the  water  collects, 
has  not  only  for  its  object  to  prevent  the  liquefaction  of  the  chloride  of 
calcium,  but  enables  the  analyst  also  to  test  the  condensed  water  as  to  its 
reaction  and  purity. 

The  apparatus  may,  of  course,  be  modified  in  various  ways  ; thus,  the 
chloride  of  calcium  tubes  may  be  XJ-shaped ; a U-tube,  filled  with  pieces 
of  pumice-stone  saturated  with  sulphuric  acid,  may  be  substituted  for  the 
flask  with  sulphuric  acid  ; and  the  gasometer  may  be  replaced  by  an  aspi- 
rator (fig.  21)  joined  to  o. 

The  expulsion  of  the  aqueous  vapor  from  the  tube  containing  the  sub- 
stance under  examination,  into  the  chloride  of  calcium  tube,  may  be 
effected  also  by  other  means  than  a current  of  air  supplied  by  a gasometer 
or  aspirator ; Viz.,  the  substance  under  examination  may  be  heated  to 
redness  in  a perfectly  dry  tube,  together  with  carbonate  of  lead,  since  the 
carbonic  acid  of  the  latter,  escaping  at  a red  heat,  serves  here  the  same 
purpose  as  a stream  of  air.  This  method  is  principally  applied  in  cases 

* [It  is  usually  better  to  weigh  off  the  substance  into  a tray  or  boat  of  porcelain 
or  platinum,  and  place  this  within  a straight  tube  of  hard  glass  and  ignite  by  means 
of  a tube  furnace.] 


46 


OPERATIONS. 


L§  37. 

where  it  is  desirable  to  retain  an  acid  which  otherwise  would  volatilize 
together  with  the  water  ; thus,  it  is  applied,  for  instance,  for  the  direct 
estimation  of  the  water  contained  in  the  bisulphate  of  potassa,  &c. 


Fig.  26. 


Fig.  26  represents  the  disposition  of  the  apparatus. 

a b is  a common  combustion  furnace  ; c f'  a tube  filled  as  follows 
from  c to  d with  carbonate  of  lead,*  from  d to  e the  substance  intimately 
mixed  with  carbonate  of  lead,  and  from  e to /‘pure  carbonate  of  lead.  The 
chloride  of  calcium  tube  y,  being  accurately  weighed,  is  connected  with 
the  tube  c by  means  of  a well-dried  perforated  cork,  f'. 

The  operation  is  commenced  by  surrounding  the  tube  with  red-hot 
charcoal,  advancing  from  f'  toward  c;  the  fore  part  of  the  tube  which 
protrudes  from  the  furnace  should  be  maintained  at  a degree  of  heat  which 
barely  permits  the  operator  to  lay  hold  of  it  with  his  fingers.  All  further 
particulars  of  this  operation  will  be  found  in  the  chapter  on  organic  ele- 
mentary analysis.  The  mixing  is  performed  best  in  the  tube  with  a wire. 
The  tube  c fr  may  be  short  and  moderately  narrow. 

The  volatilization  of  an  acid  cannot  in  all  cases  be  prevented  by  oxide  of 
lead;  thus,  for  instance,  we  could  not  determine  the  water  in  crystallized 
boracic  acid  by  the  above  process.  This  could  readily  be  done,  however, 
by  igniting  the  acid  mixed  with  excess  of  dry  carbonate  of  soda  in  a glass 
tube  drawn  out  behind  in  the  form  of  a beak,  receiving  the  water  in  a 
chloride  of  calcium  tube,  and  transferring  the  final  residue  of  aqueous 
vapor  into  the  Ca  Cl-tube  by  suction,  after  the  point  of  the  beak  has  been 
broken  off.  (See  Organic  Analysis.) 

The  foregoing  methods  for  the  direct  estimation  of  water  do  not,  how- 
ever, yet  embrace  all  cases  in  which  those  described  in  § 35  are  inap- 
plicable ; since  they  can  be  employed  only  if  the  substances  escaping 
along  with  the  water  are  such  as  will  not  wholly  or  partly  condense  in 
the  chloride  of  calcium  tube  (or  in  a hydrate  of  potassa  tube,  or  one 
filled  with  pumice-stone  saturated  with  sulphuric  acid,  which  might  be 
used  instead).  Thus  they  are  perfectly  well  adapted  for  determining 
the  water  in  the  basic  carbonate  of  zinc,  but  they  cannot  be  applied  to 
determine  the  water  in  sulphate  of  soda  and  ammonia.  With  sub- 
stances like  the  latter,  we  must  either  have  recourse  to  the  processes  of 
organic  elementary  analysis,  or  we  must  rest  satisfied  with  the  indirect 
estimation  of  the  water. 

§ 37. 

3.  Solution  of  Substances. 

Before  pursuing  the  analytical  process  further,  it  is  in  most  cases  ne- 
cessary to  obtain  a solution  of  the  substance.  This  operation  is  simple 
where  the  body  may  be  dissolved  by  direct  treatment  with  water,  or 
acids,  or  alkalies,  &c. ; but  it  is  more  complicated  in  cases  where  the 
body  requires  fluxing  as  an  indispensable  preliminary  to  solution. 

* The  carbonate  of  lead  must  have  been  previously  ignited  to  incipient  decom- 
position, and  cooled  in  a closed  tube. 


SOLUTION1. 


47 


§ 38.1 

When  we  have  mixed  substances  to  operate  upon,  the  component  parts 
of  which  behave  differently  with  solvents,  it  is  not  by  any  means  neces- 
sary to  dissolve  the  whole  substance  at  first ; on  the  contrary,  the  sepa- 
ration may,  in  such  cases,  be  often  effected,  in  the  most  simple  and  ex- 
peditious manner,  by  the  solvents  themselves.  Thus,  for  instance,  a 
mixture  of  nitrate  of  potassa,  carbonate  of  lime,  and  sulphate  of  baryta, 
may  be  readily  and  accurately  analyzed  by  dissolving  out,  in  the  first 
place,  the  nitrate  of  potassa  with  water,  and  subsequently  the  carbonate 
of  lime  by  hydrochloric  acid,  leaving  the  insoluble  sulphate  of  baryta. 

§ 38. 

a.  Direct  Solution. 

The  direct  solution  of  substances  is  effected,  according  to  circum- 
stances, in  beakers,  flasks,  or  dishes,  and  may,  if  necessary,  be  promoted 
by  the  application  of  heat ; for  which  purpose  the  water-bath  will  be 
found  most  convenient.  In  cases  where  an  open  fire,  or  the  Sand-bath, 
or  an  iron-plate  is  resorted  to,  the  analyst  must  take  care  to  guard  against 
actual  ebullition  of  the  fluid,  since  this  would  render  a loss  of  substance 
from  spirting  almost  unavoidable,  especially  in  cases  where  the  process 
is  conducted  in  a dish.  Fluids  containing  a sediment,  either  insoluble, 
or,  at  least,  not  yet  dissolved,  will,  when  heated  over  the  lamp,  often 
bump  and  spirt  even  at  temperatures  far  short  of  the  boiling-point. 

In  cases  where  the  solution  of  a substance  is  attended  with  evolution 
of  gas,  the  process  is  conducted  in  a flask,  placed  in  a sloping  position, 
so  that  the  spirting  drops  may  be  thrown  against  the  walls  of  the  vessel, 
and  thus  secured  from  being  carried  off  with  the  stream  of  the  evolved 
gas ; or  it  may  be  conducted  in  a beaker,  covered  with  a large-sized 
watch-glass,  which,  after  the  solution  is  effected,  and  the  gas  expelled  by 
heating  on  the  water-bath,  must  be  thoroughly  rinsed  with  the  washing- 
bottle. 

In  cases  where  the  solution  has  to  be  effected  by  means  of  concentrated 
volatile  acids  (hydrochloric  acid,  nitric  acid,  aqua  regia),  the  operation 
should  never  be  conducted  in  a dish,  but  always  in  a flask  covered  with 
a watch-glass,  or  placed  in  a slanting  position,  and  the  application  of  too 
high  a temperature  must  be  avoided.  The  operation  should  always  be 
conducted  also  under  a hood,  with  proper  draught,  to  carry  off  the  es- 
caping acid  vapors.  In  my  own  laboratory,  I use  for  the  latter  purpose 
the  following  simple  contrivance  : a leaden  pipe,  permanently  fixed  in  a 
convenient  position,  leads  from  the  working  table  through  the  wall  or 
the  window-frame  into  the  open  air.  The  end  in  the  laboratory  is  con- 
nected with  one  of  the  mouths  of  a two-necked  bottle  which  contains  a 
little  water.  The  other  mouth  of  the  bottle  is  closed  with  a perforated 
cork,  bearing  a firmly-fixed  glass  tube  bent  at  a right  angle ; the  portion 
of  the  tube  which  enters  the  bottle  must  not  dip  into  the  water.  The 
solution-flask  being  now  closed  with  a perforated  cork,  or  an  india-rub- 
ber cap,  bearing  a glass  tube,  connected  by  means  of  india-rubber  with 
the  bent  tube  in  the  doubled-necked  bottle,  the  vapors  evolved  are  car- 
ried out  of  the  laboratory  without  the  least  inconvenience  to  the  operator ; 
moreover,  no  receding  of  fluid  upon  cooling  need  be  apprehended.  In- 
stead of  conveying  the  vapors  away  through  a tube  leading  into  the 
open  air,  a conical  glass-tube  filled  with  pieces  of  broken  glass,  moist 


48 


OPERATIONS. 


ened  with  water  or  solution  of  carbonate  of  soda,  may  be  fixed  on  the 
second  mouth  of  the  double-necked  bottle.  I,  however,  prefer  the  other 
method.  In  some  cases,  it  is  advisable  also  to  conduct  the  escaping  va- 
pors into  a little  water,  and,  when  solution  has  been  effected,  make  the 
water  recede  by  withdrawing  the  lamp,  since  this  will,  at  the  same  time, 
serve  to  dilute  the  solution;  care  must  be  taken,  however,  to  guard 
against  a premature  receding  of  the  water  in  consequence  of  an  acci- 
dental cooling  of  the  solution  flask. 

It  is  often  necessary,  in  conducting  a process  of  solution,  to  guard 
against  the  action  of  the  atmospheric  oxygen ; in  such  cases,  a slow 
stream  of  carbonic  acid  is  transmitted  through  the  solution-flask ; in 
some  cases  it  is  sufficient  to  expel  the  air,  by  simply  first  putting  a little 
bicarbonate  of  soda  into  the  flask,  containing  an  excess  of  acid,  before 
introducing  the  substance. 


§ 39. 

b.  Solution,  preceded  by  Fluxing. 

Substances  insoluble  in  water,  acids,  or  aqueous  alkalies,  usually 
require  decomposition  by  fluxing,  to  prepare  them  for  analysis.  Sub- 
stances of  this  kind  are  often  met  w'ith  in  the  mineral  kingdom;  most 
silicates,  the  sulphates  of  the  alkaline  earths,  chrome  ironstone,  &c., 
belong  to  this  class. 

The  object  and  general  features  of  the  process  of  fluxing  have  already 
been  treated  of  in  the  qualitative  part  of  the  present  work.  The  special 
methods  of  conducting  this  important  operation  will  be  described  here- 
after under  “ The  analysis  of  silicates,”  and  in  the  proper  places ; as  a 
satisfactory  description  of  the  process,  with  its  various  modifications, 
cannot  well  be  given  without  entering  more  minutely  into  the  particular 
circumstances  of  the  several  special  cases. 

Decomposition  by  fluxing  often  requires  a higher  temperature  than  is 
attainable  with  a spirit-lamp  with  double  draught,  or  with  a common 
gas-lamp.  In  such  cases,  the  glass-blower’s  lamp,  fed  with  gas,  is  used 
with  advantage. 


§ 40. 

4.  Conversion  of  the  dissolved  Substance  into  a weighable  Form. 

The  conversion  of  a substance  in  a state  of  solution  into  a form  adapted 
for  weighing  may  be  effected  either  by  evaporation  or  by  precipitation. 
The  former  of  these  operations  is  applicable  only  in  cases  where  the  sub- 
stance, the  weight  of  which  we  are  desirous  to  ascertain,  either  exists 
already  in  the  solution  in  the  form  suitable  for  the  determination  of  its 
weight,  or  may  be  converted  into  such  form  by  evaporation  in  conjunction 
with  some  reagent.  The  solution  must,  moreover,  contain  the  substance 
unmixed,  or,  at  least,  mixed  only  with  such  bodies  as  are  expelled  by 
evaporation  or  at  a red-heat.  Thus,  for  instance,  the  amount  of  sulphate 
of  soda  present  in  an  aqueous  solution  of  that  substance  may  be  ascer- 
tained by  simple  evaporation  ; whilst  the  carbonate  of  potassa  contained 
in  a solution  would  better  be  converted  into  chloride  of  potassium,  by 
evaporating  with  solution  of  chloride  of  ammonium. 

Precipitation  may  always  be  resorted  to,  whenever  the  substance  in 


EVAPORATION. 


49 


§41.] 

solution  admits  of  being  converted  into  a combination  which  is  insoluble 
in  the  menstruum  present,  provided  that  the  precipitate  is  fit  for  deter- 
mination, which  can  never  be  the  case  unless  it  can  be  washed  and  is  of 
constant  composition. 


§ 41. 

a.  Evaporation. 

In  processes  of  evaporation  for  pharmaceutical  or  technico-chemical 
purposes  the  principal  object  to  be  considered  is  saving  of  time  and  fuel ; 
but  in  evaporating  processes  in  quantitative  analytical  researches  this  is. 
merely  a subordinate  point,  and  the  analyst  has  to  direct  his  principal 
care  and  attention  to  the  means  of  guarding  against  loss  or  contamina- 
tion of  the  substance  operated  upon. 

The  simplest  case  of  evaporation  is  when  we  have  to  concentrate  a 
clear  fluid , without  carrying  the  process  to  dryness.  To  effect  this  object, 
the  fluid  is  poured  into  a basin,  which  should  not  be  filled  to  more  than 
two-thirds.  Heat  is  then  applied  by  placing  the  basin  either  on  a water- 
bath,  sand-bath,  common  stove,  or  heated  iron  plate,  or  over  the  flame 
of  a gas-  or  spirit-lamp,  care  being  taken  always  to  guard  against  actual 
ebullition,  as  this  invariably  and  unavoidably  leads  to  loss  from  small 
drops  of  fluid  spirting  out.  Evaporation  over  a gas  or  spirit-lamp,  when 
conducted  with  proper  care,  is  an  expeditious  and  cleanly  process.  Bun- 
sen’s gas-lamp  may  be  used  most  advantageously  in  operations  of  this 
kind  ; a little  wire-gauze  cap,  loosely  fitted  upon  the  tube  of  the  lamp,  is 
a material  improvement.  By  means  of  this  simple  arrangement  it  is 
easy  to  produce  even  the  smallest  flame,  without  the  least  apprehension 
of  ignition  of  the  gas  within  the  tube. 

If  the  evaporation  is  to  be  effected  on  the 
water-bath,  and  the  operator  happens  to  possess 
a Beindorf,  or  other  similarly-constructed  steam 
apparatus,  the  evaporating-dish  may  be  placed 
simply  into  an  opening  corresponding  in  size. 

Otherwise  recourse  must  be  had  to  the  water-bath, 
illustrated  by  fig.  27. 

It  is  made  of  strong  sheet  copper,  and  when 
used  is  half  filled  with  water,  which  is  kept  boiling  over  a gas-,  spirit-,  or 
oil-lamp.  The  breadth  from  a to  b should  be  from  12  to  18  cm.  Vari- 
ous flat  rings  of  the  same  outside  diameter  as  the  top  of  the  bath,  and 
adapted  to  receive  dishes  and  crucibles  of  different  sizes,  are  essential 
adjuncts  to  the  bath.  These  rings  when  required  are  simply  laid  on  the 
bath. 

It  will  occasionally  happen  that  the  water  in  the  bath  completely 
evaporates ; in  such  cases,  residues  are  heated  to  a higher  degree  than  is 
desirable,  concentrated  solutions  spirt,  &c.  To  avoid  these  inconve- 
niences, a water-bath  with  constant  level  is  employed.  Such  a bath  is 
shown  in  fig.  , p.  , where  the  reader  will  find  its  description. 

If  the  operator  can  conduct  his  processes  of  evaporation  in  a room  set 
apart  for  the  purpose,  where  he  may  easily  guard  against  any  occurrence 
tending  to  suspend  dust  in  the  air,  he  will  find  it  no  very  difficult  task  to 
keep  the  evaporating  fluid  clean ; in  this  case  it  is  best  to  leave  the  dishes 
uncovered.  But  in  a large  laboratory,  frequented  by  many  people,  or  in 
4 


Fig.  27. 


50 


OPERATIONS. 


[§  41. 


Fig:.  29. 


a room  exposed  to  draughts  of  air,  or  in  which  coal  fires  are  burning,  the 
greatest  caution  is  required  to  protect  the  evaporating  fluid  from  contami- 
nation by  dust  or  ashes. 

For  this  purpose  the  evaporating  dish  is  either  covered  with  a sheet  of 
filtering-paper  turned  down  over  the  edges,  or  a glass  rod  twisted  into  a 
triangular  shape  (fig.  28)  is  laid  upon  it,  and  a 
sheet  of  filtering-paper  spread  over  it,  which  is 
kept  in  position  by  a glass  rod  laid  across,  the 
latter  again  being  kept  from  rolling  down  by  the 
slightly  turned  up  ends,  a and  6,  of  the  triangle. 

The  best  way,  however,  is  the  following : — 
Take  two  small  thin  wooden  hoops  (fig.  29),  one 
of  which  fits  loosely  in  the  other ; spread  a sheet  of  blotting-paper  over 
the  smaller  one,  and  push  the  other  over  it.  This  forms  a cover  admirably 
adapted  to  the  purpose ; and  whilst  in  no  way 
interfering  with  the  operation,  it  completely  pro- 
tects the  evaporating  fluid  from  dust,  and  may 
be  readily  taken  off ; the  paper  cannot  dip  into  the 
fluid ; the  cover  lasts  a long  time,  and  may, 
moreover,  at  any  time  be  easily  renewed. 

It  must  be  borne  in  mind,  however,  that  the  common  filtering-paper 
contains  always  certain  substances  soluble  in  acids,  such  as  lime,  sesqui- 
oxide  of  iron,  &c.,  which,  were  covers  of  the  kind  just  described  used  over 
evaporating  dishes  containing  a fluid  evolving  acid  vapors,  would  infallibly 
dissolve  in  these  vapors,  and  the  solution  dripping  down  into  the  evapo- 
rating fluid,  would  speedily  contaminate  it.  Care  must  be  taken,  there- 
fore, in  such  cases,  to  use  only  such  filtering-paper  as  has  been  freed  by 
washing  from  substances  soluble  in  acids. 

Evaporation  for  the  purpose  of  concentration  may  be  effected  also 
in  flasks ; these  are  only  half  filled,  and  placed  in  a slanting  position. 
The  process  may  be  conducted  on  the  sand-bath,  or  over  a gas-  or  spirit- 
lamp,  or  even,  and  with  equal  propriety,  over  a charcoal  fire.  In  cases 
where  the  operation  is  conducted  over  a lamp  or  a charcoal  fire,  it  is  the 
safest  way  to  place  the  flasks  on  wire  gauze.  Gentle  ebullition  of  the 
fluid  can  do  no  harm  here,  since  the  slanting  position  of  the  flask  guards 
effectively  against  risk  of  loss  from  the  spirting  of  the  liquid.  Still  better 
than  in  flasks,  the  object  may  be  attained  by  evaporating  in  tubulated 
retorts  with  open  tubulure  and  neck  directed  obliquely  upwards.  The 
latter  acts  as  a chimney,  and  the  constant  change  of  air  thus  effected  is 
extremely  favorable  to  evaporation. 

The  evaporation  of  fluids  containing  a precipitate  is  best  conducted  on 
the  water- bath ; since  on  the  sand-bath,  or  over  the  lamp,  it  is  next  to 
impossible  to  guard  against  loss  from  bumping.  This  bumping  is  occa- 
sioned by  slight  explosions  of  steam,  arising  from  the  sediment  impeding 
the  uniform  diffusion  of  the  heat.  Still  there  remains  another,  though 
less  safe  way,  viz,,  to  conduct  the  evaporation  in  a crucible  placed  in  a 
slanting  position,  as  illustrated  in  fig.  30.  In  this  process,  the  flame  is 
made  to  play  upon  the  crucible  above  the  level  of  the  fluid. 

Where  a fluid  has  to  he  evaporated  to  dryness , as  is  so  often  the  case,  the 
operation  should  always,  if  possible,  be  terminated  on  the  water-bath.  In 
cases  where  the  nature  of  the  dissolved  substance  precludes  the  applica- 
tion of  the  water-batfi,  the  object  in  view  may  often  be  most  readily 
attained  by  heating  the  .contents  of  the  dish  from  the  top,  which  is 


EVAPORATION. 


51 


§«•] 

effected  by  placing  the  dish  in  a proper  position  in  a drying  closet,  whose 
upper  plate  is  heated  by  a flame  (that  of  the  water-  or  sand-bath)  passing 
over  it.  If  the  substance  is  in  a covered  platinum  dish  or  crucible,  place  the 
gas-lamp  in  such  a position  that  the  flame  may  act  on  the  cover  from  above. 

In  cases  where  the  heat  has  to  be  applied 
from  the  bottom,  a method  must  be  chosen 
which  admits  of  an  equal  diffusion  and  ready 
regulation  of  the  heat. 

An  air-bath  is  well  adapted  for  this  purpose, 
i.e .,  a dish  of  iron  plate,  in  which  the  porcelain 
or  platinum  dish  is  to  be  placed  on  a wire  tri- 
angle, so  that  the  two  vessels  may  be  at  all 
points  \ to  inch  distant  from  each  other. 

The  copper  apparatus,  fig.  27,  may  also  serve 
as  an  air-bath,  although  I must  not  omit  to 
mention  that  this  mode  of  application  will  in 
the  end  seriously  injure  it.  If  the  operation  has 
to  be  conducted  over  a lamp,  the  dish  should  be 
placed  high  above  the  flame ; best  on  wire 
gauze,  since  this  will  greatly  contribute  to  an 
equal  diffusion  of  the  heat.  The  use  of  the 
sand-bath  is  objectionable  here,  because  with 
that  apparatus  we  cannot  reduce  the  heat  so  speeder  as  may  be  desira- 
ble. An  iron  plate  heated  by  gas  may  perhaps  be*^cd  with  advantage. 
But  no  matter  which  method  be  employed,  this  rule  applies  equally  to 
all  of  them  ; that  the  operator  must  watch  the  process,  from  the  moment 
that  the  residue  begins  to  thicken,  in  order  to  prevent  spirting,  by  redu- 
cing the  heat,  and  breaking  the  pellicles  which  form  on  the  surface,  with 
a glass  rod,  or  a platinum  wire  or  spatula. 

Saline  solutions  that  have  a tendency , upon  their  evaporation , to  creep 
up  the  sides  of  the  vessel , and  may  thus  finally  pass  over  the  brim  of  the 
latter,  thereby  involving  the  risk  of  a loss  of  substance,  should  be  heated 
from  the  top,  in  the  way  just  indicated  ; since  by  that  means  the  sides 
of  the  vessel  will  get  heated  sufficiently  to  cause  the  instantaneous  evap- 
oration of  the  ascending  liquid,  preventing  thus  its  overflowing  the 
brim.  The  inconvenience  just  alluded  to  may,  however,  be  obviated 
also,  in  most  cases,  by  covering  the  brim,  and  the  uppermost  part  of  the 
inner  side  of  the  vessel,  with  a very  thin  coat  of  tallow,  thus  diminish- 
ing the  adhesion  between  the  fluid  and  the  vessel. 

In  the  case  of  liquids  evolving  gas-bubbles  upon  evaporating , particu- 
lar caution  is  required  to  guard  against  loss  from  spirting.  The  safest 
way  is  to  heat  such  liquids  in  an  obliquely-placed  flask,  or  in  a beaker 
covered  with  a large  watch-glass ; the  latter  is  removed  as  soon  as  the 
evolution  of  gas-bubbles  has  ceased,  and  the  fluid  that  may  have  spirted 
up  against  it  is  carefully  rinsed  into  the  glass,  by  means  of  a washing- 
bottle.  If  the  evaporation  has  to  be  conducted  in  a dish,  a rather 
capacious  one  should  be  selected,  and  a very  moderate  degree  of  heat  ap- 
plied at  first,  and  until  the  evolution  of  gas  has  nearly  ceased. 

If  a fluid  has  to  be  evaporated  with  exclusion  of  air,  the  best  way  is 
to  place  the  dish  under  the  bell  of  an  air-pump,  over  a vessel  with  sul- 
phuric acid,  and  to  exhaust ; or  a tubulated  retort  may  be  used,  through 
whose  tubulure  hydrogen  or  carbonic  acid  is  passed  by  the  aid  of  a tube 
not  quite  reaching  to  the  surface  of  the  fluid. 


52 


OPERATIONS. 


I §42. 

The  material  of  the  evaporating  vessels  may  exercise  a much  greater 
influence  on  the  results  of  an  analysis  than  is  generally  believed.  Many 
rather  startling  phenomena  that  are  observed  in  analytical  processes  may 
arise  simply  from  a contamination  of  the  evaporated  liquid  by  the  mate- 
rial of  the  vessel ; great  errors  may  also  spring  from  the  same  source. 

The  importance  of  this  point  has  induced  me  to  subject  it  to  a search- 
ing investigation  (see  Appendix,  Analytical  Experiments,  1 — 4),  of 
which  I will  here  briefly  intimate  the  results. 

Distilled  water  kept  boiling  for  some  length  of  time  in  glass  (flasks  of 
Bohemian  glass)  dissolves  very  appreciable  traces  of  that  material.  This 
is  owing  to  the  formation  of  soluble  silicates ; the  particles  dissolved 
consist  chiefly  of  potassa,  or  soda  and  lime,  in  combination  with  silicic 
acid.  A much  larger  proportion  of  the  glass  is  dissolved  by  water  contain- 
ing caustic  or  carbonated  alkali  ; boiling  solution  of  chloride  of  ammo- 
nium also  strongly  attacks  glass  vessels.-  Boiling  dilute  acids,  with  the 
exception,  of  course,  of  hydrofluoric  and  hydrofluosilicic  acids,  exercise  a 
less  powerful  solvent  action  on  glass  than  pure  water.  Porcelain  (Berlin 
dishes)  is  much  less  affected  by  water  than  glass ; alkaline  liquids  also  ex- 
ercise a less  powerful  solvent  action  on  porcelain  than  on  glass  ; the 
quantity  dissolved  is,  however,  still  notable.  Solution  of  chloride  of  am- 
monium acts  on  porcelain  as  strongly  as  on  glass ; dilute  acids,  though 
exercising  no  very  powerful  solvent  action  on  porcelain,  yet  attack  that 
material  more  strongly  than  glass.  It  results  from  these  data,  that  in 
analyses  pretending  to  a high  degree  of  accuracy,  platinum  or  platinum- 
iridium  or  silver  dishes  should  always  be  preferred.  The  former  may 
be  used  in  all  cases  where  no  free  chlorine,  bromine,  or  iodine  is  present 
in  the  fluid,  or  can  be  formed  during  evaporation.  Fluids  containing 
caustic  alkalies  may  safely  be  evaporated  in  platinum,  but  not  to  the 
point  of  fusion  of  the  residue.  Silver  vessels  should  never  be  used  to  evap- 
orate acid  fluids  nor  liquids  containing  alkaline  sulphides ; but  they  are 
admirably  suited  for  solutions  of  caustic  and  carbonated  alkalies,  as  well 
as  of  most  neutral  salts. 

§ 42* 

We  come  now  to  weighing  the  residues  remaining  upon  the  evapo- 
ration of  fluids.  We  allude  here  simply  to  such  as  are  soluble  in 
water  ; those  which  are  separated  by  filtration  will  be  treated  of  afterwards. 
.Residues  are  generally  weighed  in  the  same  vessel  in  which  the  evaporation 
has  been  completed,  for  which  purpose  platinum  dishes,  from  4 to  8 cm.  in 
diameter,  provided  with  light  covers,  or  large  plati- 
num crucibles,  are  best  adapted,  since  they  are 
lighter  than  porcelain  vessels  of  the  same  capacity. 

However,  in  most  cases,  the  amount  of  liquid 
to  be  evaporated  is  too  large  for  so  small  a vessel, 
and  its  evaporation  in  portions  would  occupy  too 
much  time.  The  best  way,  in  cases  of  this  kind, 
is  to  concentrate  the  liquid  first  in  a larger  vessel, 
and  to  terminate  the  operation  afterwards  in  the 
smaller  weighing  vessel. 

In  transferring  the  fluid  from  the  larger  to  the 
smaller  vessel,  the  lip  of  the  former  is  slightly 
greased',  and  the  liquid  made  to  run  down  a glass  rod.  (See  fig.  31.) 


PRECIPITATION. 


53 


Finally  the  large  vessel  is  carefully  rinsed  with  a washing-bottle,  until  a 
drop  of  the  last  rinsing  leaves  no  longer  a residue  upon  evaporation  on  a 
platinum  knife.  When  the  fluid  has  thus  been  transferred  to  the  weigh- 
ing-vessel, the  evaporation  is  completed  on  the  water-bath  and  the  resi- 
duary substance  finally  ignited,  provided,  of  course,  it  will  admit  of  this 
process.  For  this  purpose  the  dish  is  covered  with  a lid  of  thin  plati- 
num (or  a thin  glass  plate),  and  then  placed  high  over  the  flame  of  a 
lamp,  and  heated  very  gently  until  all  the  water  which  may  still  adhere 
to  the  substance  is  expelled  ; the  dish  is  now  exposed  to  a stronger,  and 
finally  to  a red-heat.  (Where  a glass  plate  is  used,  this  must,  of  course, 
be  removed  before  igniting.)  In  this  case  it  is  also  well  to  make  the 
flame  play  obliquely  on  the  cover  from  above,  so  as  to  run  as  little  risk 
as  possible  of  loss  by  spirting.  After  cooling  in  a desiccator,  the  covered 
dish  is  weighed  with  its  contents.  When  operating  upon  substances 
which  decrepitate,  such  as  chloride  of  sodium,  for  instance,  it  is  advisa- 
ble to  expose  them — after  their  removal  from  the  water-bath,  and  pre- 
viously to  the  application  of  a naked  flame — to  a temperature  somewhat 
above  100°,  either  in  the  air-bath,  or  on  a sand-bath,  or  on  a common 
stove. 

If  the  residue  does  not  admit  of  ignition,  as  is  the  case,  for  instance, 
with  organic  substances,  ammoniacal  salts,  &c.,  it  is  dried  at  a tempera- 
ture suited  to  its  nature.  In  many  cases,  the  temperature  of  the  water- 
bath  is  sufficiently  high  for  this  purpose,  for  the  drying  of  chloride  of  am- 
monium, for  instance ; in  others,  the  air  or  oil-batli  must  be  resorted  to. 
(See  §§  29  and  30.)  Under  any  circumstances,  the  desiccation  must  be 
continued  until  the  substance,  ceases  to  suffer  the  slightest  diminution 
in  weight,  after  renewed  exposure  to  heat  for  half  an  hour.  The  dish 
should  invariably  be  covered  during  the  process  of  weighing. 

If,  as  will  frequently  happen,  we  have  to  deal  with  a fluid  containing 
a small  quantity  of  a salt  of  potassa  or  soda,  the  weight  of  which  we 
want  to  ascertain,  in  presence  of  a comparatively  large  amount  of  a salt 
of  ammonia,  which  has  been  mixed  with  it  in  the  course  of  the  analytical 
process,  I prefer  the  following  method : The  saline  mass  is  thoroughly 

dried,  in  a large  dish,  on  the  water-bath,  or,  towards  the  end  of  the  pro- 
cess, at  a temperature  somewhat  exceeding  100°.  The  dry  mass  is  then, 
with  the  aid  of  a platinum  spatula,  transferred  to  a small  glass  dish, 
which  is  put  aside  for  a time  in  a desiccator.  The  last  traces  of  the 
salt  left  adhering  to  the  sides  and  bottom  of  the  large  dish  are  rinsed  off 
with  a little  water  into  the  small  dish,  or  the  large  crucible,  in  which  it 
is  intended  to  weigh  the  salt ; the  water  is  then  evaporated,  and  the  dry 
contents  of  the  glass  dish  are  added  to  the  residue : the  ammonia  salts 
are  now  expelled  by  ignition,  and  the  residuary  fixed  salts  finally  weighed. 
Should  some  traces  of  the  saline  mass  adhere  to  the  smaller  glass  dish, 
they  ought  to  be  removed  and  transferred  to  the  weighing  vessel,  with 
the  aid  of  a little  pounded  chloride  of  ammonium,  or  some  other  salt 
of  ammonia,  as  the  moistening  again  with  water  would  involve  an  almost 
certain  loss  of  substance. 

§ 43. 

b.  Precipitation. 

Precipitation  is  resorted  to  in  quantitative  analysis  far  more  frequently 
than  evaporation,  since  it  serves  not  merely  to  convert  substances  into 


54 


OPERATIONS. 


forms  adapted  for  weighing,  but  also,  and  more  especially,  to  separate 
them  from  one  another.  The  principal  intention  in  precipitation,  for  the 
purpose  of  quantitative  estimations,  is  to  convert  the  substance  in  solu- 
tion into  a form  in  which  it  is  insoluble  in  the  menstruum  present. 
The  result  will,  therefore,  cocteris  paribus , be  the  more  accurate,  the 
more  the  precipitated  body  deserves  the  epithet  insoluble,  and  in  cases 
where  precipitates  are  of  the  same  degree  of  solubility,  that  one  will 
suffer  the  least  loss  which  comes  in  contact  with  the  smallest  amount  of 
solvent. 

Hence  it  follows,  first,  that  in  all  cases  where  other  circumstances  do 
not  interfere,  it  is  preferable  to  precipitate  substances  in  their  most  inso- 
luble form ; thus,  for  instance,  baryta  had  better  be  precipitated  as  sul- 
phate than  as  carbonate ; secondly,  that  when  we  have  to  deal  with  pre- 
cipitates that  are  not  quite  insoluble  in  the  menstruum  present,  we  must 
endeavor  to  remove  that  menstruum,  as  far  as  practicable,  by  evapora- 
tion ; thus  a dilute  solution  of  strontia  should  be  concentrated,  before 
proceeding  to  precipitate  the  strontia  with  sulphuric  acid  ; and,  thirdly, 
that  when  we  have  to  deal  with  precipitates  slightly  soluble  in  the  liquid 
present,  but  insoluble  in  another  menstruum,  into  which  the  former  may 
be  converted  by  the  addition  of  some  substance  or  other,  we  ought  to 
endeavor  to  bring  about  this  modification  of  the  menstruum.  Thus,  for 
instance,  alcohol  may  be  added  to  water,  to  induce  complete  precipita- 
tion of  chloride  of  platinum  and  ammonium,  chloride  of  lead,  sulphate 
of  lime,  &c.  ; thus  again,  the  basic  phosphate  of  magnesia  and  ammonia 
may  be  rendered  insoluble  in  an  aqueous  menstruum  by  adding  ammonia 
to  the  latter,  &c. 

Precipitation  is  generally  effected  in  beakers.  In  cases,  however, 
where  we  have  to  precipitate  from  fluids  in  a state  of  ebullition,  or 
where  the  precipitate  requires  to  be  kept  boiling  for  some  time  with 
the  fluid,  flasks  or  dishes  are  substituted  for  beakers,  with  due  regard 
always  to  the  material  of  which  they  are  made  (see  Evaporation,  § 41, 
at  the  end). 

The  separation  of  precipitates  from  the  fluid  in  which  they  are  sus- 
pended, is  effected  either  by  decantation  or  filtration , or  by  both  these 
processes  jointly.  But,  before  proceeding  to  the  separation  of  the  pre- 
cipitate by  any  of  these  methods,  the  operator  must  know  whether  the 
precipitant  has  been  added  in  sufficient  quantity,  and  whether  the  pre- 
cipitate is  completely  formed.  To  determine  the  latter  point,  an  accurate 
knowledge  of  the  properties  of  the  various  precipitates  must  be  attained, 
which  we  shall  endeavor  to  supply  in  the  third  section.  To  decide  the 
former  question,  it  is  usually  sufficient  to  add  to  the  fluid  (after  the  pre- 
cipitate has  settled)  cautiously  a fresh  portion  of  the  precipitant,  and  to 
note  if  a further  turbidity  ensues.  This  test,  however,  is  not  infallible, 
when  the  precipitate  has  not  the  property  of  forming  immediately ; as, 
for  instance,  is  the  case  with  phospho-molybdate  of  ammonia.  When  this 
is  apprehended,  pour  out  (or  transfer  with  a pipette)  a small  quantity 
of  the  clear  supernatant  fluid  into  another  vessel,  add  some  of  the  pre- 
cipitant, warm,  if  necessary  ; and  after  some  time  look  and  see  whether 
a fresh  precipitate  has  formed.  As  a general  rule,  the  precipitated  liquid 
should  be  allowed  to  stand  at  rest  for  several  hours,  before  proceeding  to 
the  separation  of  the  precipitate.  This  rule  applies  more  particularly 
to  crystalline,  pulverulent,  and  gelatinous  precipitates,  whilst  curdy  and 
flocculent  precipitates,  more  particularly  when  the  precipitation  was 


!§  44,  45.] 


FILTRATION. 


55 


effected  at  a boiling  temperature,  may  often  be  filtered  off  immediately. 
However,  we  must  observe  here,  that  all  general  rules,  in  this  respect, 
are  of  limited  application. 


§ 44- 

a.  Separation  of  Precipitates  by  Decantation. 

When  a precipitate  subsides  so  completely  and  speedily  in  a fluid  that 
the  latter  may  be  decanted  off  perfectly  clear,  or  drawn  off  with  a 
syphon,  or  removed  by  means  of  a pipette,  and  that  the  washing  of  the 
precipitate  does  not  require  a very  long  time,  decantation  is  often  resorted 
to  for  its  separation  and  washing ; this  is  the  case,  for  instance,  with 
chloride  of  silver,  metallic  mercury,  &c. 

Decantation  will  always  be  found  a very  expeditious  and  accurate 
method  of  separation,  if  the  process  be  conducted  with  due  care ; it  is 
necessary,  however,  in  most  cases,  to  promote  the  speedy  and  complete 
subsidence  of  the  precipitate  ; and  it  may  be  laid  down  as  a general  rule, 
that  heating  the  precipitate  with  the  fluid  will  produce  the  desired  effect. 
Nevertheless,  there  are  instants  in  which  the  simple  application  of  heat 
will  not  suffice ; in  some  cases,  as  with  chloride  of  silver,  for  instance, 
agitation  must  be  resorted  to ; in  other  cases,  some  reagent  or  other  is 
to  be  added — hydrochloric  acid,  for  instance,  in  the  precipitation  of  mer- 
cury, &c.  We  shall  have  occasion,  subsequently,  in  the  fourth  section, 
to  discuss  this  point  more  fully,  when  we  shall  also  mention  the  vessels 
best  adapted  for  the  application  of  this  process  to  the  various  precipitates. 

After  having  washed  the  precipitate  repeatedly  with  fresh  quantities 
of  the  proper  fluid,  until  there  is  no  trace  of  a dissolved  substance  to  be 
detected  in  the  last  rinsings,  it  is  placed  in  a crucible  or  dish,  if  not 
already  in  a vessel  of  that  description ; the  fluid  still  adhering  to  it  is 
poured  off*  as  far  as  practicable,  and  the  precipitate  is  then,  according  to 
its  nature,  either  simply  dried,  or  heated  to  redness. 

A far  larger  amount  of  water  being  required  for  washing  precipitates 
by  decantation  than  on  filters,  the  former  process  can  be  expected  to 
yield  accurate  results  only  where  the  precipitates  are  absolutely  in- 
soluble. For  the  same  reason,  decantation  is  not  ordinarily  resorted  to 
in  cases  where  we  have  to  determine  other  constituents  in  the  decanted 
fluid. 

The  decanted  fluid  must  be  allowed  to  stand  at  rest  from  twelve  to 
twenty-four  hours,  to  make  quite  sure  that  it  contains  no  particles  of 
the  precipitate  ; if,  after  the  lapse  of  this  time,  no  precipitate  is  visible, 
the  fluid  may  be  thrown  away ; but  if  a precipitate  has  subsided,  this 
had  better  be  estimated  by  itself,  and  the  weight  added  to  the  main 
amount;  the  precipitate  may,  in  such  cases,  be  separated  from  the 
supernatant  fluid  by  decantation,  or  by  filtration. 

§45. 

15.  Separation  of  Precipitates  by  Filtration. 

This  operation  is  resorted  to  whenever  decantation  is  impracticable, 
and,  consequently,  in  the  great  majority  of  cases ; provided  always  the 
precipitate  is  of  a nature  to  admit  of  its  being  completely  freed,  by  mere 


56 


OPERATIONS. 


[ §45. 

washing  on  the  filter,  from  all  foreign  substances.  Where  this  is  not 
the  case,  more  particularly,  therefore,  with  gelatinous  precipitates,  hy- 
drate of  alumina  for  instance,  a combination  of  decantation  and  filtra- 
tion is  resorted  to  (§  48). 

act.  Filtering  Apparatus. 

Filtration,  as  a process  of  quantitative  analysis,  is  almost  exclusively 
effected  by  means  of  paper. 

Plain  circular  filters  are  most  generally  employed ; plaited  filters  are 
only  occasionally  used.  Much  depends  upon  the  quality  of  the  paper. 
Good  filtering-paper  must  possess  the  three  following  properties: — 1. 
It  must  completely  retain  the  finest  precipitates ; 2.  It  must  filter  rap- 
idly ; and  3.  It  must  be  as  free  as  possible  from  any  admixture  of  inor- 
ganic bodies,  but  more  especially  from  such  as  are  soluble  in  acid  or 
alkaline  fluids. 

It  is  a matter  of  some  difficulty,  however,  to  procure  paper  fully  an- 
swering these  conditions.  The  Swedish  filtering  paper,  with  the  water- 
mark J.  H.  Munktell,  is  considered  the  best,  and,  consequently,  fetches 
the  highest  price ; but  even  this  answers  only  the  first  two  conditions, 
being  by  no  means  sufficiently  pure  for  very  accurate  analyses,  since  it 
leaves  upon  incineration  about  0’3  per  cent,  of  ash,*  and  yields  to  acids 
perceptible  traces  of  lime,  magnesia,  and  sesquioxide  of  iron.  F or  exact 
experiments  it  is,  consequently,  necessary  first  to  extract  the  paper  with 
dilute  hydrochloric  acid,  then  to  wash  the  acid  completely  out  with 
water,  and  finally  to  dry  the  paper.  In  the  case  of  very  fine  filtering- 
paper,  the  best  way  to  perform  this  operation  is  to  place  the  ready-cut  fil- 
ters, several  together,  in  a funnel,  exactly  the  same  way  as  if  intended  for 
immediate  filtration  ; they  are  then  moistened  with  a mixture  of  one  part 
of  ordinary  pure  hydrochloric  acid  with  two  parts  of  water,  which  is  al- 
lowed to  act  on  them  for  about  ten  minutes ; after  this  all  traces 
of  the  acid  are  carefully  removed  by  washing  the  filters  in  the 
funnel  repeatedly  with  warm  water.  The  funnel  being  then  covered 
with  a piece  of  paper,  turned  over  the  edges,  is  put  in  a warm  place  un- 
til the  filters  are  dry.  Compare  the  instruction  given  in  the  “ Qual. 
Anal.,”  Am.  Ed.,  p.  8,  on  the  preparation  of  washed  filters.  Filter  paper 
containing  lead,  and  which  is  consequently  blackened  by  sulphuretted 
hydrogen,  should  be  rejected. 

Ready-cut  filters  of  various  sizes  should  always  be  kept  on  hand. 
Filters  are  either  cut  by  circular  patterns  of  pasteboard  or  tin,  or,  still 

better,  by  Mohr’s  filter-patterns, 
fig.  32.  This  little  apparatus  is 
made  of  tin-plate,  and  consists  of 
two  parts.  I>  is  a quadrant  fit- 
ting in  A , whose  straight  edges 
are  turned  up,  and  which  is  slight- 
ly smaller  than  J3.  The  sheets  of 
filter-paper  are  first  cut  up  into 
squares,  which  are  folded  in  quar- 

* Plantamour  found  the  ash  of  Swedish  filtering  paper  to  consist  of  63  23  sili- 
cic acid,  12-83  lime,  6-21  magnesia,  2 94  alumina,  and  13  92  sesquioxide  of  iron, 
in  100  parts. 


FILTRATION. 


57 


§45.1 


ters,  and  placed  in  A ; then  B is  placed  on  the  top,  and  the  free  edge 
of  the  paper  is  cut  off  with  scissors.  Filters  cut  in  this  way  are  perfectly 
circular,  and  of  equal  size. 

Several  pairs  of  these  patterns  of  various  sizes  (3,  4,  5,  6,  6 -5,  and  8 
cm.  radius)  should  be  procured.  In  taking  a filter  for  a given  opera- 
tion, you  should  always  choose  one  which,  after  the  fluid  has  run 
through,  will  not  be  more  than  half  filled  with  the  precipitate. 

As  to  the  funnels,  they  should  be  inclined  at  the  angle  of  60°,  and 
not  bulge  at  the  sides.  Glass  is  the  most  suitable  material  for  them. 


The  filter  should  never  protrude  beyond  the  funnel.  It  should  come 
up  to  one  or  two  lines  from  the  edge  of  the  latter. 

The  filter  is  firmly  pressed  into  the  funnel,  to  make  the  paper  fit  closely 
to  the  side  of  the  latter  ; it  is  then  moistened  with  water ; any  extra  water 
is  not  poured  out,  but  allowed  to  drop  through. 

The  stands  shown  in  figs.  33  and  34  complete  the  apparatus  for  filter- 
ing. 

[The  stand  in  fig.  34  serves  at  once  as  support  for  the  funnel  and 
cover  for  the  receiving  vessel.  The  funnel  is  sustained  by  a ring  of  wood 
of  such  height  that  only  the  neck  of  the  funnel  comes  below  the  shelf. 
The  shelf  is  10  cm.,  and  the  ring  15  cm.  thick.  The  opening  of  the  ring 
above  is  30  cm.] 

The  stands  are  made  of  hard  wood.  The  arm  holding  the  funnel  or 
funnels  must  slide  easily  up  and  down,  and  be  fixable  by  the  screw. 
The  holes  for  the  funnels  must  be  cut  conically,  to  keep  the  funnels  steadily 
in  their  place. 

These  stands  are  very  convenient,  and  may  be  readily  moved  about 
without  interfering  with  the  operation. 


\ 


Fig.  33. 


Fig.  34. 


58 


OPERATIONS. 


[§  46. 


§ 46. 

bb.  Rules  to  be  observed  in  the  Process  of  Filtration. 

In  the  case  of  curdy,  flocculent,  gelatinous,  or  crystalline  precipitates 
there  is  no  danger  of  the  fluid  passing  turbid  through  the  filter.  But 
with  fine  pulverulent  precipitates  it  is  generally  necessary,  and  always 
advisable , to  let  the  precipitate  subside,  and  then  filter  the  supernatant 
liquid,  before  proceeding  to  place  the  precipitate  upon  the  filter.  We 
generally  proceed  in  this  way  also  with  other  kinds  of  precipitates,  espe- 
cally  with  those  that  require  to  stand  long  before  they  completely  separate. 
Precipitates  which  have  been  thrown  down  hot,  are  most  properly  filtered 
off  before  cooling  (provided  always  there  be  no  objections  to  this  course), 
since  hot  fluids  run  through  the  filter  more  speedily  than  cold  ones.  Some 
precipitates  have  a tendency  to  be  carried  through  the  filter  along  with  the 
fluid  ; this  may  be  prevented  in  some  instances  by  modifying  the  latter. 
Thus  sulphate  of  baryta,  when  filtered  from  an  aqueous  solution,  passes 
rather  easily  through  the  filter — the  addition  of  hydrochloric  acid  or 
chloride  of  ammonium  prevents  this  in  a great  measure. 

If  the  operator  finds,  during  a filtration,  that  the  filter  would  be  much 
more  than  half  filled  by  the  precipitate,  he  would  better  use  an  additional 
filter,  and  thus  distribute  the  precipitate  over  the  two  ; for,  if  the  first 
were  too  full,  the  precipitate  could  not  be  properly  washed. 

The  fluid  ought  never  to  be  poured  directly  upon  the  filter,  but  always 
down  a glass  rod,  and  the  lip  or  rim  of  the  vessel  from  which  the  fluid  is 
poured  should  always  be  slightly  greased  with  tallow.*  The  stream 
ought  invariably  to  be  directed  towards  the  sides  of  the  filter,  never  to 
the  centre,  since  this  might  occasion  loss  by  splashing.  In  cases  where 
the  fluid  has  to  be  filtered  off,  with  the  least  possible  disturbance  of  the 
precipitate,  the  glass  rod  must  not  be  placed,  during  the  intervals,  in  the 
vessel  containing  the  precipitate  ; but  it  may  conveniently  be  put  into 
a clean  glass,  which  is  finally  rinsed  with  the  wash-water. 

The  filtrate  is  received  either  in  flasks,  beakers,  or  dishes,  according  to 
the  various  purposes  for  which  it  may  be  intended.  Strict  care  should  be 
taken  that  the  drops  of  fluid  filtering  through  glide  down  the  side  of  the 
receiving  vessel ; they  should  never  be  allowed  to  fall  into  the  centre  of 
the  filtrate,  since  this  again  might  occasion  loss  by  splashing.  The  best 
method  is  that  shown  in  fig.  34,  viz.,  to  rest  the  point  of  the  funnel  against 
the  upper  part  of  the  inside  of  the  receiving  vessel. 

If  the  process  of  filtration  is  conducted  in  a place  perfectly  free  from 
dust,  there  is  no  necessity  to  cover  the  funnel,  nor  the  vessel  receiving  the 
filtrate ; however,  as  this  is  but  rarely  the  case,  it  is  generally  indispensable 
to  cover  both.  This  is  best  effected  with  round  plates  of  sheet-glass. 
The  plate  used  for  covering  the  receiving  vessel  should  have  a small 
U-shaped  piece  cut  out  of  its  edge,  large  enough  for  the  funnel-tube  to 
go  through.  The  effect  desired  may  be  produced  by  cautiously  chipping 
out  the  glass  bit  by  bit  with  the  aid  of  a key.  Plates  perforated  in  the 
centre  are  worthless  as  regards  the  object  in  view. 

After  the  fluid  and  precipitate  have  been  transferred  to  the  filter,  and 
the  vessel  which  originally  contained  them  has  been  rinsed  repeatedly  with 


* The  tallow  may  be  kept  under  the  edge  of  the  work-table  at  a convenient 
point,  where  it  will  adhere  by  a little  pressure.  The  best  way  of  applying  the 
tallow  to  the  lip  of  a vessel  is  with  the  greased  finger. 


FILTRATION. 


59 


§47.] 

water,  it  happens  generally  that  small  particles  of  the  precipitate  remain 
adhering  to  the  vessel,  which  cannot  be  removed  with  the  glass  rod.  From 
beakers  or  dishes  these  particles  may  be  readily  removed  by  means  of  a 
feather  prepared  for  the  purpose  by  tearing  off  nearly  the  whole  of  the 
plumules,  leaving  only  a small  piece  at  the  end  which  should  be  cut  per- 
fectly straight.  From  flasks,  minute  portions  of  heavy  precipitates  which 
are  not  adherent,  are  readily  removed  by  blowing  a jet  of  water  into  the 
flask,  held  inverted  over  the  funnel ; this  is  effected  by  means  of  the 
washing-bottle  shown  in  fig.  36.  If  the  minute  adhering  particles  of  a 
precipitate  cannot  be  removed  by  mechanical  means,  solution  in  an 
appropriate  menstruum  must  be  resorted  to,  followed  by  re -precipitation. 
Bodies  for  which  we  possess  no  solvent,  such  as  sulphate  of  baryta,  for 
instance,  must  not  be  precipitated  in  flasks. 

§ 47. 

cc.  Washing  of  Precipitates. 

After  having  transferred  the  precipitate  completely  to  the  filter,  we 
have  next  to  perform  the  operation  of  washing  ; this  is  effected  by  means 
of  one  of  the  well-known  washing-bottles,  of  which  I prefer  the  one 
represented  in  fig.  35  in  every  respect.  The  doubly  perforated  stoppers 
are  of  vulcanized  rubber. 


Fig.  37. 

Care  must  always  be  taken  to  properly  regulate  the  jet,  as  too  impetu- 
ous a stream  of  water  might  occasion  loss  of  substance. 

In  cases  where  a precipitate  has  to  be  washed  with  great  caution,  the 
apparatus  illustrated  in  fig.  37  will  be  found  to  answer  very  well. 

The  construction  of  this  apparatus  requires  no  explanation.  When 
the  flask  is  inverted,  it  supplies  a fine  continuous  jet  of  water. 

Precipitates  requiring  washing  with  water,  are  washed  most  expe- 
ditiously with  hot  water,  provided  always  there  be  no  special  reason 
against  its  use.  The  washing-bottle  shown  in  fig.  35  is  particularly  well 
adapted  for  this  purpose.  The  cork  which  is  fastened  to  the  neck  of  the 
flask  with  wire  serves  to  facilitate  holding  it. 

It  is  a rule  in  washing  precipitates  not  to  add  fresh  wash-water  to  the 
filter  till  the  old  has  quite  run  through.  In  applying  the  jet  of  water  you 
have  to  take  care  on  the  one  hand  that  the  upper  edge  of  the  filter  is 


60 


OPERATIONS. 


L§  48. 


properly  washed,  and  on  the  other  hand  that  no  canals  are  formed  in  the 
precipitate,  through  which  the  fluid  runs  off,  without  coming  in  contact 
with  the  whole  of  the  precipitate.  If  such  canals  have  formed  and  cannot 
be  broken  up  by  the  jet,  the  precipitate  must  be  stirred  cautiously  with  a 
small  platinum  knife  or  glass  rod. 

The  washing  may  be  considered  completed  when  all  soluble  matter  that 
is  to  be  removed  has  been  got  rid  of.  The  beginner  who  devotes  proper 
attention  to  the  completion  of  this  operation  shuns  one  of  the  rocks  which 
he  is  most  likely  to  encounter.  Whether  the  precipitate  has  been  com- 
pletely washed  may  generally  be  ascertained  by  slowly  evaporating  a drop 
of  the  last  washings  upon  a platinum  knife,  and  observing  if  a residue  is 
left.  But  in  cases  where  the  precipitate  is  not  altogether  insoluble  in 
water  (sulphate  of  strontia,  for  instance),  recourse  must  be  had  to  more 
special  tests,  which  we  shall  have  occasion  to  point  out  in  the  course  of 
the  work.  The  student  should  never  discontinue  the  washing  of  a pre- 
cipitate because  he  simply  imagines  it  is  finished — he  must  be  certain. 


§ 48. 


y.  Separation  of  Precipitates  by  Decantation  and  Filtration 

CpMBINED. 

In  the  case  of  precipitates  which,  from  their  gelatinous  nature,  or  from 
the  firm  adhesion  of  certain  coprecipitated  salts,  oppose  insuperable,  or,  at 
all  events,  considerable  obstacles  to  perfect  washing  on  the  filter,  the  fol- 
lowing method  is  resorted  to  : Let  the  precipitate  subside  as  far  as  prac- 
ticable, pour  the  nearly  clear  supernatant  liquid  on  the  filter,  stir  the  pre- 
cipitate up  with  the  washing  fluid  (in  certain  cases,  where  such  a course 
is  indicated,  heat  to  boiling),  let  it  subside  again,  and  repeat  this  opera- 
tion until  the  precipitate  is  almost  thoroughly  washed.  Transfer  it  now 
to  the  filter,  and  complete  the  operation  with  the  washing-bottle  (see 
§ 47).  This  method  is  highly  to  be  recommended  ; there  are  many  pre- 
cipitates that  can  be  thoroughly  washed  only  by  its  application. 

In  cases  where  it  is  not  intended  to  weigh  the  precipitate  washed  by 
decantation,  but  to  dissolve  it  again,  the  operation  of  washing  is  entirely 
completed  by  decantation,  and  the  precipitate  not  even  transferred  to  the 
filter.  The  re-solution  of  the  bulk  of  the  precipitate  being  effected  in  the 
vessel  containing  it,  the  filter  is  placed  over  the  latter,  and  the  solvent 
passed  through  it.  Although  the  termination  of  the  operation  of  washing 
may  be  usually  ascertained  by  testing  a sample  of  the  washings  for  one  of 
the  substances  originally  present  in  the  solution  which  has  to  be  removed 
(for  hydrochloric  acid,  for  instance,  with  nitrate  of  silver),  still  there  are 
cases  in  which  this  mode  of  proceeding  is  inapplicable.  In  such  cases,  and 
indeed  in  processes  of  washing  by  decantation  generally,  Bunsen’s  method 
will  be  found  convenient — viz.,  to  continue  the  process  of  washing  until 
the  fluid  which  had  remained  in  the  beaker,  after  the  first  decantation, 
has  undergone  a ten  thousand-fold  dilution.  To  effect  this,  measure 
with  a slip  of  paper  the  height  from  the  bottom  of  this  beaker  to  the  sur- 
face of  the  fluid  remaining  in  it,  together  with  the  precipitate,  after  the 
first  decantation  ; then  fill  the  beaker  with  water,  if  possible,  boiling,  and 
measure  the  entire  height  of  the  fluid ; divide  the  length  of  the  second 
column  by  that  of  the  first.  Go  through  the  same  process  each  time  you 
add  fresh  water,  and  always  multiply  the  quotient  found  with  the  number 
obtained  in  the  preceding  calculation,  until  you  reach  10000. 


§§  49,  50.] 


DRYING  OF  PRECIPITATES. 


61 


§ 49. 

Further  Treatment  of  Precipitates. 

Before  proceeding  to  weigh  a precipitate,  it  still  remains  to  convert  it 
into  a form  of  accurately  known  composition.  This  is  done  either  by 
igniting  or  by  drying.  The  latter  proceeding  is  more  protracted  and 
tedious  than  the  former,  and  is,  moreover,  apt  to  give  less  accurate  results. 
The  process  of  drying  is,  therefore,  as  a general  rule,  applied  only  to  pre- 
cipitates which  cannot  bear  exposure  to  a red  heat  without  undergoing 
total  or  partial  volatilization ; or  whose  residues  left  upon  ignition  have 
no  constant  composition ; thus,  for  instance,  drying  is  resorted  to  in  the 
case  of  sulphide  of  mercury,  sulphide  of  arsenic,  and  other  metallic  sul- 
phides ; and  also  in  the  case  of  cyanide  of  silver,  double  chloride  of 
platinum  and  potassium,  &c. 

But  whenever  the  nature  of  the  precipitate  (e.g.,  sulphate  of  baryta, 
sulphate  of  lead,  and  many  other  compounds)  leaves  the  operator  at 
liberty  to  choose  between  drying  and  heating  to  redness,  the  latter  pro- 
cess is  almost  invariably  preferred. 


§ 50- 

act.  Drying  of  Precipitates. 

When  a precipitate  has  been  collected,  washed,  and  dried  on  a filter, 
minute  particles  of  it  adhere  so  firmly  to  the  paper  that  it  is  found 
impossible  to  remove  them.  The  weighing  of  dried  precipitates  in- 
volves, therefore,  in  all  accurate  analyses,  the  drying  and  weighing  of 
the  filter  also.  To  obtain  accurate  results,  it  is  necessary  to  dry  and 
weigh  the  filter  before  using  it ; the  temperature  at  which  the  filter  is 
dried  must  be  the  same  as  that  to  which  it  is  intended  subsequently 
to  expose  the  precipitate.  Another  condition  is  that  the  filtering-paper 
must  not  contain  any  substance  liable  to  be  dissolved  by  the  fluid  pass- 
ing through  it. 

The  drying  is  conducted  either  in  the  water-,  air-,  or  oil-bath,  accord- 
ing to  the  degree  of  heat  required.  The  weighing  is  performed  in  a 
closed  vessel,  mostly  between  two  clasped  watch-glasses  (fig.  20),  or  in  a 
platinum  crucible.  When  the  filter  appears  dry,  it  is  placed  between  the 
warm  watch-glasses,  or  in  the  warm  crucible,  allowed  to  cool  under  a 
bell-glass,  over  sulphuric  acid,  and  weighed.  The  reopened  crucible  or 
watch-glasses,  together  with  the  filter,  are  then  again  exposed  for  some 
time  to  the  required  degree  of  heat,  and,  after  cooling,  weighed  once 
more.  If  the  weight  does  not  differ  from  that  found  at  first,  the  filter 
may  be  considered  dry,  and  we  have  simply  to  note  the  collective  weight 
of. the  watch-glasses,  clasp,  and  filter,  or  of  the  crucible  and  filter. 

After  the  washing  of  the  precipitate  has  been  concluded  and  the  water 
allowed  to  run  off  as  far  as  possible,  the  filter  with  the  precipitate  is  taken 
off  the  funnel,  folded  up,  and  placed  upon  blotting-paper,  which  is  then 
kept  for  some  time  in  a moderately  warm  place  protected  from  dust ; it  is 
finally  put  into  one  of  the  watch-glasses,  or  into  the  uncovered  platinum 
crucible,  with  which  it  was  first  weighed,  and  exposed  to  the  appropriate 
degree  of  heat,  either  in  the  water-,  air-,  or  oil-bath.  When  it  is  judged 
that  the  precipitate  is  dry,  the  second  watch-glass,  or  the  lid  of  the  crucible 
is  put  on  (with  the  clasp  pushed  over  the  two  in  the  former  case),  and  the 


62 


OPERATIONS. 


[§  81. 


whole,  after  cooling  in  the  desiccator,  is  weighed.  The  filter  and  the 
precipitate  are  then  again  exposed,  in  the  same  way,  to  the  proper  drying 
temperature,  allowed  to  cool,  and  weighed  again,  the  same  process  being 
repeated  until  the  weight  remains  constant  or  varies  only  to  the  extent 
of  a few  deci-milligrammes.  By  subtracting  from  the  weight  found  the 
tare  of  the  crucible  or  watch-glasses  and  filter,  we  obtain  the  weight  of 
the  dry  precipitate.  [The  filter  must  not  be  dried  too  long,  as  it  slowly 
loses  weight,  and  even  becomes  brown  from  decomposition  when  heated  to 
100°  for  days  together.] 

It  happens  sometimes  that  the  precipitate  nearly  fills  the  filter,  or  retains 
a considerable  amount  of  water ; or  sometimes  the  paper  is  so  thin  that  its 
removal  from  the  funnel  cannot  well  be  effected  without  tearing.  In  all 
such  cases,  the  best  way  is  to  let  the  filter  and  precipitate  get  nearly  dry 

in  the  funnel,  which  may  be  effected  readily 
by  covering  the  latter  with  a piece  of  blotting- 
paper*  to  keep  out  the  dust,  and  placing  it, 
supported  on  a broken  beaker  (fig.  38),  or 
some  other  vessel  of  the  kind,  on  the  steam- 
apparatus  or  sand-bath,  or  stove,  or  on  a 
heated  iron  plate.  For  support  to  a funnel 
while  drying  a hollow  frustum  of  a cone  open 
both  ends,  made  of  sheet  zinc  (fig.  39),  is  con- 
venient. Two  sizes  may  be  used,  10  cm.  and  12  cm.  high  respectively. 
The  lower  diameter  should  be  from  7 to  8,  the  upper  from  4 to  6 cm. 


Fig.  38. 


Fig.  39. 


§ 51. 

bb.  Ignition  of  Precipitates. 

In  this  process  it  is  necessary  to  burn  the  filter  and  subtract  the 
weight  of  the  filter  ash  from  the  total  weight  found. 

If  care  be  taken  to  make  the  filters  always  of  the  same  paper,  and  to  cut 
every  size  by  a pattern,  the  quantity  of  ash  which  each  size  yields  upon 
incineration  may  be  readily  determined.  It  is  necessary,  however,  to 
determine  separately  the  quantity  of  ash  left  by  ordinary  filters,  and  that 
left  by  filters  which  have  been  washed  with  hydrochloric  acid  and  water  ; 
on  an  average  the  latter  lea  ve  about  half  as  much  ash  as  the  former.  To 
determine  the  filter  ash  take  ten  filters  (or  an  equal  weight  of  cuttings 
from  the  same  paper),  burn  them  in  an  obliquely-placed  platinum  crucible, 
and  ignite  until  every  trace  of  carbon  is  consumed ; then  weigh  the  ash, 
and  divide  the  amount  found  by  ten  ; the  quotient  expresses,  with  suf- 
ficient precision,  the  average  quantity  of  ash  which  every  individual  filter 
leaves  upon  incineration. 

In  the  ignition  of  precipitates,  the  following  four  points  have  to  be 
more  particularly  regarded : 

1.  No  loss  of  substance  must  be  incurred  ; 

2.  The  ignited  precipitates  must  really  be  the  bodies  they  are  repre- 
sented to  be  in  the  calculation  of  the  results; 


* Turned  down  over  the  rim.  Or  more  neatly  as  follows  : — Wet  a common  cut 
filter,  stretch  it  over  the  ground  top  of  the  funnel,  and  then  gently  tear  off  the 
superfluous  paper.  The  cover  thus  formed  continues  to  adhere  after  drying  with 
some  force. 


IGNITION  OF  PRECIPITATES. 


63 


8 51.] 

3.  The  incineration  of  the  filters  must  be  complete  ; 

4.  The  crucibles  must  not  be  attacked. 

The  following  two  methods  seem  to  me  the  simplest  and  most  appro- 
priate of  all  that  have  as  yet  been  proposed.  The  selection  of  either 
depends  upon  certain  circumstances,  which  I shall  immediately  have  occa- 
sion to  point  out.  But  no  matter  which  method  is  resorted  to,  the  pre- 
cipitate must  always  be  thoroughly  dried,  before  it  can  properly  be  exposed 
to  a red  heat.  The  application  of  a red  heat  to  moist  precipitates,  more 
particularly  to  such  as  are  very  light  and  loose  in  the  dry  state  (silicic 
acid,  for  instance),  involves  always  a risk  of  loss  from  the  impetuously 
escaping  aqueous  vapors  carrying  away  with  them  minute  particles  of  the 
substance.  Some  other  substances,  as  hydrate  of  alumina  or  hydrated 
sesquioxide  of  iron,  for  instance,  form  small  hard  lumps  ; if  such  lumps 
are  ignited  while  still  moist  within  they  are  liable  to  fly  about  with  great 
violence.  The  best  method  of  drying  precipitates  as  a preliminary  to 
ignition  is  as  described  in  § 50,  the  last  paragraph. 

Respecting  the  ignition,  the  degree  of  heat  to  be  applied  and  the  dura • 
tion  of  the  process  must,  of  course,  depend  upon  the  nature  of  the  pre- 
cipitate and  upon  its  deportment  at  a red  heat.  As  a general  rule,  a 
moderate  red  heat,  applied  for  about  five  minutes,  is  found  sufficient  to 
effect  the  purpose  ; there  are,  however,  many  exceptions  to  this  rule 
which  will  be  indicated  wherever  they  occur. 

Whenever  the  choice  is  permitted  between  porcelain  and  platinum 
crucibles,  the  latter  are  always  preferred,  on  account  of  their  comparative 
lightness  and  infrangibilixy,  and  because  they  are  more  readily  heated  to 
redness.  The  crucible  selected  should  always  be  of  sufficient  capacity,  as 
the  use  of  crucibles  deficient  in  size  involves  the  risk  of  loss  of  substance. 
The  proper  size,  in  most  cases,  is  4 cm.  in  height,  and  3 ’5  cm.  in  diameter. 
That  the  crucible  must  be  perfectly  clean,  both  inside  and  outside,  need 
hardly  be  mentioned.  The  analyst  should  acquire  the  habit  of  cleaning 
and  polishing  the  platinum  crucible  always  after  using  it.  This  should 
be  done  by  friction  with  moist  sea-sand  whose  grains  are  all  round  and 
do  not  scratch.  The  sand  is  rubbed  on  with  the  finger,  and  the  desired 
effect  is  produced  in  a few  minutes.  The  adoption  of  this  habit  is 
attended  with  the  pleasure  of  always  working  with  a bright  crucible  and 
the  profit  of  prolonging  its  existence.  This  mode  of  cleaning  is  all  the 
more  necessary,  when  one  ignites  over  gas-lamps,  since  at  this  high  tem- 
perature crucibles  soon  acquire  a gray  coating,  which  arises  from  a super- 
ficial loosening  of  the  platinum.  A little  burnishing  with  sea-sand 
readily  removes  the  appearance  in  question,  without  causing  any  notable 
diminution  of  the  weight  of  the  crucible.  The  foregoing  remarks  on 
platinum  crucibles  refer  equally  to  those  of  iridium-platinum — which, 
by-the-by,  are  now  much  used,  and  very  highly  to  be  recommended — 
only  the  restoration  of  the  polish  is  somewhat  more  difficult  with  the 
latter,  on  account  of  the  greater  hardness  of  the  alloy.  If  there  are 
spots  on  the  platinum  or  iridium-platinum  crucibles,  which  cannot  be 
removed  by  the  sand  without  wearing  away  too  much  of  the  metal,  a 
little  bisulphate  of  potassa  is  fused  in  the  crucible,  the  fluid  mass  shaken 
about  inside,  allowed  to  cool,  and  the  crucible  finally  boiled  with  water. 
There  are  two  ways  of  cleaning  crucibles  soiled  outside  ; either  the  cruci- 
ble is  placed  in  a larger  one,  and  the  interspace  filled  with  bisulphate  of 
potassa,  which  is  then  heated  to  fusion ; or  the  crucible  is  placed  on  a 
platinum-wire  triangle,  heated  to  redness,  and  then  sprinkled  over  with 


64 


OPERATIONS. 


13  52 


powdered  bisulphate  of  potassa.  Instead  of  the  bisnlphate  you  may  use 
borax.  Never  forget  at  last  to  polish  the  crucible  with  sea-sand  again. 

When  the  crucible  is  clean,  it  is  placed  upon 
a clean  platinum-wire  triangle  (fig.  40),  ig- 
nited, allowed  to  cool  in  the  desiccator,  and 
weighed.  This  operation,  though  not  indis- 
pensable, is  still  always  advisable,  that  the 
weighing  of  the  empty  and  the  filled  crucible 
may  be  performed  under  as  nearly  as  possible 
the  same  circumstances.  The  empty  crucible 
may  of  course  be  weighed  after  the  ignition  of 
the  precipitate ; however,  it  is  preferable  in 
most  cases  to  weigh  it  before.  The  ignition  is 
effected  with  a Berzelius  spirit-lamp  or  a gas-lamp,  or  else  in  a muffle. 
In  igniting  reducible  substances  over  lamps,  the  analyst  must  always  be 
on  his  guard  against  the  contact  of  unconsumed  hydrocarbons  even  in 
covered  crucibles.  When  gas-lamps  are  used  there  is  especial  need  of 
caution  in  this  respect.  Reduction  will  be  avoided  if  the  flame  is  made 
no  larger  than  necessary,  if  the  crucible  is  supported  in  the  upper  part 
of  the  flame,  and  if,  when  the  crucible  is  in  a slanting  position,  it  is 
heated  from  behind. 

We  pass  on  now  to  the  description  of  the  special  methods. 


§ 52. 


First  Method.  ( Ignition  of  the  Precipitate  with  the  Filter, 


This  method  is  resorted  to  in  cases  where  there  is  no  danger  of  a re- 
duction of  the  precipitate  by  the  action  of  the  carbon  of  the  filter.  The 
mode  of  proceeding  is  as  follows : — 

The  perfectly  dry  filter,  with  the  precipitate,  is  removed  from  the  fun- 
nel, and  its  sides  are  gathered  together  at  the  top,  so  that  the  precipitate 
lies  enclosed  as  in  a small  bag.  The  filter  is  now  put  into  the  crucible, 
which  is  then  covered  and  heated  over  a spirit-lamp  with  double  draught, 
or  over  gas  very  gently,  to  effect  the  slow  charring  of  the  filter ; the  cover 
is  now  removed,  the  crucible  placed  obliquely,  and  a stronger  degree  of 
heat  applied,  until  complete  incineration  of  the  filter  is  effected ; the  lid, 
which  had  in  the  meantime  best  be  kept  on  a porcelain  plate,  or  in  a 
porcelain  crucible,  is  put  on  again,  and  a red  heat  applied  for  some  time 
longer,  if  needed ; the  crucible  is  now  allowed  to  cool  a little,  and  is 
then,  while  still  hot,  though  no  longer  red  hot,*  taken  off  with  a pair  of 
tongs  of  brass  or  polished  iron  (fig.  41),  and  put  in  the  desiccator,  where 
it  is  left  to  cool ; it  is  finally  weighed. 

The  combustion  of  the  carbon  of  the  filter  may  be  promoted,  in  cases 
where  it  proceeds  too  slowly,  by  pushing  the  non-consumed  particles, 
with  a smoth  and  rather  stout  platinum  wire,  within  the  focus  of  the 
strongest  action  of  the  heat  and  air.  And  the  operator  may  also  in- 
crease the  draught  of  air  by  leaning  the  lid  of  the  crucible  against  the 
latter  in  the  manner  illustrated  in  fig.  42. 

It  will  occasionally  happen  that  particles  of  the  carbon  of  the  filter 


* Taking  bold  of  a red  hot  crucible  with  brass  tongs  might  cause  the  forma- 
tion of  black  rings  round  it. 


53.] 


IGNITION  OF  PRECIPITATES. 


65 


obstinately  resist  incineration.  In  such  cases  the  operation  may  be  pro- 
moted by  putting  a small  lump  of  fused,  dry  nitrate  of  ammonia  into 
the  crucible,  placing  on  the  lid  and  applying  a gentle  heat  at  first,  which 
is  gradually  increased.  However,  as  this  way  of  proceeding  is  apt  to  in- 
volve some  loss  of  substance,  its  application  should  not  be  made  a gene- 
ral rule. 


In  cases  where  the  bulk  of  the  precipitate  is  easily  detached  from  the 
filter,  the  preceding  method  is  occasionally  modified  in  this,  that  the 
precipitate  is  put  into  the  crucible,  and  the  filter,  with  the  still  adhe- 
ring particles,  folded  loosely  together,  and  laid  over  the  precipitate. 
In  other  respects,  the  operation  is  conducted  in  the  manner  above 
described. 

§ 53- 

Second  Method.  ( Ignition  of  the  Precipitate  apart  from  the  Filter .) 

This  method  is  resorted  to  in  cases  where  a reduction  of  the  precipi- 
tate from  the  action  of  the  carbon  of  the  filter  is  apprehended  ; and  also 
where  the  ignited  precipitate  is  required  for  further  examination,  which 
the  presence  of  the  filter  ash  might  embarrass.  It  may  be  employed 
also,  instead  of  the  first  method,  in  all  cases  where  the  precipitate  is 
easily  detached  from  the  filter.  The  mode  of  proceeding  is  as  fol- 
lows : — 

The  crucible  intended  to  receive  the  precipitate  is  placed  upon  a sheet 
of  glazed  paper ; the  perfectly  dry  filter  with  the  precipitate  is  taken 
out  of  the  funnel,  and  gently  pressed  together  over  the  paper,  to  detach 
the  precipitate  from  the  filter ; the  precipitate  is  now  shaken  into  the 
crucible,  and  the  particles  still  adhering  to  the  filter  are  removed  from 
it,  as  far  as  practicable,  by  further  pressing  or  gentle  rubbing  together 
of  the  folded  filter,  and  are  then  also  transferred  to  the  crucible.  The 
filter  is  now  spread  open  upon  the  sheet  of  glazed  paper,  and  then  folded 
in  form  of  a little  square  box,  enclosed  on  all  sides  by  the  parts  turned  up ; 

5 


06 


OPERATIONS. 


any  minute  particles  of  the  precipitate  that  may  have  dropped  on  the 
glazed  paper  are  brushed  into  this  little  box,  with  the  aid  of  a small 
feather ; the  box  is  closed  again,  rolled  up,  and  one  end  of  a long  pla- 
tinum wire  spirally  wound  round  it.  The  crucible  being  placed  on  or 
above  a porcelain  plate,  the  little  roll  is  lighted,  and,  during  its  combus- 
tion, held  over  the  crucible,  so  that  the  falling  particles  of  the  precipi- 
tate or  filter  ash  may  drop  into  it,  or,  at  least,  into  the  porcelain  plate. 
In  this  way,  and  by  occasionally  holding  the  little  roll  again  in  or 
against  the  flame,  the  incineration  of  the  filter  is  readily  and  safely 
effected.  When  the  operation  is  terminated,  a slight  tap  will  suffice 
to  drop  the  ash  and  the  remaining  particles  of  the  precipitate  into 
the  crucible,  which  is  then  covered,  and  the  ignition  completed  as 
in  § 52.  Where  it  is  intended  tp  keep  the  ash  separate  from 
the  precipitate,  it  is  made  to  drop  into  the  lid  of  the  crucible,  in 
which  case  it  is  better  to  ignite  the  crucible  with  the  principal  portion 
of  the  precipitate  first.  Tliis  method  of  incinerating  the  filter,  devised 
by  Bunsen,  is  preferable  to  the  method  formerly  in  use,  in  which  the 
filter,  freed,  as  far  as  practicable,  from  the  precipitate,  was  burnt  either 
whole  or  cut  up  into  little  bits  on  the  lid  of  the  crucible,  the  operation 
being  promoted  when  necessary  by  gently  pressing  the  still  unconsumed 
particles  with  a platinum  wire,  or  platinum  spatula,  against  the  red-hot 
lid.  No  matter  which  method  of  incineration  is  resorted  to,  the  ope- 
ration must  always  be  conducted  in  a spot  entirely  protected  from 
draughts. 

Certain  precipitates  suffer  some  essential  modification  in  their  pro- 
perties, in  their  solubility,  for  instance,  from  ignition.  In  cases  where 
a portion  of  a substance  of  the  kind  is  required,  after  the  weighing,  for 
some  other  purpose  with  which  the  effects  of  a red  heat  would  interfere, 
the  two  operations  of  drying  and  igniting  may  be  combined  in  the  fol- 
lowing way  : — The  precipitate  is  collected  on  a filter  dried  at  100°;  it  is 
then  also  dried,  at  100°,  and  weighed  (§  50).  A portion  of  the  dry  pre- 
cipitate is  put  into  a tared  crucible,  and  its  exact  weight  ascertained ; 
It  is  then  exposed  to  a red  heat,  allowed  to  cool  in  the  usual  way,  and 
weighed  again  ; the  diminution  of  weight  which  it  has  undergone  is  cal- 
culated on  the  whole  amount  of  the  precipitate. 

§ 53,  a. 

Bunsen’s  Method  of  Rapid  Filtration.* 

A precipitate  is  washed  either  by  filtration  or  by  decantation : in 
the  former  case  the  portion  of  liquid  not  mechanically  retained  is  al- 
lowed to  drain  from  the  precipitate  ; in  the  latter  it  is  separated  by 
simply  pouring  it  away,  the  foreign  substances  contained  in  the  preci- 
pitate being  then  removed  by  the  repeated  addition  of  some  washing- 
fluid,  in  each  successive  portion  of  which  the  precipitate  is,  as  far  as 
possible,  uniformly  suspended,  this  process  being  continued  until  the 
amount  of  impurity  becomes  so  minute  that  its  presence  may  be  entirely 
disregarded. 

Supposing  v to  represent  the  volume  of  the  moist  precipitate  remain- 
ing at  the  bottom  of  the  vessel  after  the  decantation,  or  upon  the  filtrate 
after  filtration,  Y the  volume  of  wash-water  employed  at  each  succes- 

* Ann.  der  Chem.  und  Pharm.,  vol.  cxlviii.  p.  269  ; Am.  Jour.  Sci.,  xlvii.  p.  321. 


53,  a.] 


bunsen’s  method  of  rapid  filtration. 


67 


sive  decantation,  n the  number  of  decantations,  and  _ the  fraction  ex- 

a 


pressing  the  proportion  of  the  original  amount  of  impurity  still  remain- 
ing in  the  precipitate  after  n decantations,  then 


Calling  W the  total  volume  of  wash-water  resulting  from  n decantations, 
then 

nY—W ; (2) 

therefore 


1 + 


W\  n 


■ \ 


ij 


« w==»e(y--i) (3) 

If  we  differentiate  W with  respect  to  yi  and  make  the  differential 
quotient  equal  to  0,  then  the  minimum  value  of  W becomes,  when 
n — oo, 

W~v  nat.  log.  a (4) 

Precipitates  obtained  in  the  course  of  chemical  analysis  may  in  all 
eases  be  assumed  to  be  sufficiently  washed  when  the  impurity  retained 
by  them  amounts  to  no  more  than  the  tWoo~o  Parfc-  Making  therefore 
a = 100000  and  v—  1,  it  results  from  equation  (4)  that  the  least 
quantity.  of  fluid  required  in  order  to  remove  the  impurity  contained  in 
a precipitate  to  the  -l  Q ^ 0 0-  part  amounts  to  eleven  and  a half  times 
the  volume  occupied  by  the  precipitate  itself  in  the  liquid  in  which  it 
exists.  It  is  evident,  therefore,  that  the  amount  of  water  actually  ne- 
cessary to  wash  a precipitate  the  more  nearly  approaches  this  minimum 
the  oftener  we  decant,  and  the  smaller  the  quantity  of  washing-water 
we  employ  at  each  decantation. 

Since  some  of  the  principal  sources  of  error  in  analytical  work  con- 
sist in  the  incomplete  or  in  the  too  protracted  washing  of  precipitates,  it 
becomes  important  to  know  how  to  ascertain  the  progress  of  the  washing 
throughout  the  several  stages  of  the  process.  By  employing  the  same 
volume  of  water  at  each  successive  addition,  and  estimating  its  relation 
to  that  of  the  precipitate  remaining  at  the  bottom  of  the  vessel  or  upon 
the  filter,  we  can  find  from  the  Table  on  the  following  page,  calculated 
by  means  of  the  formula  above  given,  the  number  of  times  it  is  neces- 
sary to  decant  in  order  to  diminish  the  amount  of  impurity  in  the  pre- 
cipitate to  the  T-ooVoTD  irofoo?  20000  or  100 00  Part-  Column  I.  shows 
the  relation  between  the  volume  of  the  precipitate  and  the  washing- 
water  employed  for  each  successive  decantation,  column  II.  the  num- 
ber of  decantations  required  to  diminish  the  amount  of  impurity  to  the 
necessary  extent,  and  column  III.  the  total  volume  of  water  obtained 
from  the  several  decantations. 

When  the  washing-process  is  performed  in  a beaker,  the  relation  be- 
tween the  volume  of  the  precipitate  and  that  of  the  liquid  may  be  easily 
determined  by  holding  a strip  of  paper  along  the  side  of  the  vessel  and 
marking  upon  it  the  respective  heights  of  the  precipitate  and  supernatant 
liquid ; then  on  folding  the  portion  of  paper  lying  between  the  two  marks 
in  such  a manner  that  each  fold  corresponds  to  the  height  occupied  by 


68 


OPERATIONS. 


the  precipitate,  the  number  of  folds  will  give  the  argument  in  column  I. 
to  find  in  column  II.  the  number  of  decantations  needed  to  wash  to  the 
required  extent.  If  the  washing  be  conducted  as  in  the  ordinary  method 
of  filtration,  funnels  possessing  an  angle  of  60°  must  be  invariably  em- 
ployed, and  the  capacities  of  the  various-sized  filters  once  for  all  deter- 
mined by  means  of  a burette.  After  the  precipitate  has  been  brought 
upon  the  filter  and  allowed  to  drain,  it  is  mixed  as  thoroughly  as  possi- 
ble with  water  from  a graduated  washing-flask.  Call  the  amount  of 
water  thus  necessary  to  fill  the  filter  p,  and  the  capacity  of  the  empty 

filter  1),  then  ^—5 — . — . — _ column  I. ; that  is,  the  argument  needed 

to  find  in  column  II.  the  number  of  times  it  is  necessary  to  refill  the  filter 
in  order  to  wash  the  precipitate  to  the  desired  extent. 


1 0 0*0  0 O' 

i 

i 

l 

• 

ToWo  o 

2 0 0 0 0 

1 0 0 0 0 

I. 

II. 

III. 

I. 

II. 

III. 

I. 

II. 

III. 

I. 

II. 

III. 

V 

n. 

W. 

V 

n. 

W. 

V 

n. 

W. 

V. 

n. 

W. 

V 

V 

V 

V 

0-5 

28-4 

14-2 

0*5 

26-7 

13*3 

0-5 

24-4 

12-2 

0*5 

22-7 

11-4 

1 

16-6 

16-6 

1 

15  6 

15  6 

1 

14-3 

14-3 

1 

13*3 

13*3 

2 

105 

21  0 

2 

9-8 

19-7 

2 

9 0 

18-0 

2 

8*4 

168 

3 

8-8 

24  9 

3 

7-8 

23  4 

3 

71 

21-4 

3 

6 6 

19  9 

4 

71 

28-6 

4 

6-7 

26  9 

4 

61 

24-6 

4 

5 7 

22  9 

5 

6 4 

32-1 

5 

6 0 

30  2 

5 

5 5 

27-6 

5 

51 

25*7 

6 

5-9 

35  5 

6 

56 

33  4 

6 

51 

30  5 

6 

4-7 

28*4 

7 

55 

38-8 

7 

5 2 

36  4 

7 

4-8 

33  3 

7 

4*4 

31-0 

8 

5-2 

42-0 

8 

49 

39  4 

8 

4-5 

361 

8 

4-2 

33*5 

9 

5 0 

45  0 

9 

4-7 

42-3 

9 

4 3 

38-7 

9 

40 

36-0 

10 

4-8 

48  0 

10 

4-5 

451 

10 

41 

413 

10 

3-8 

38*4 

11 

4-6 

5T0 

11 

4*4 

47-9 

11 

4-0 

43-8 

11 

3 7 

40-8 

12 

4-5 

53-9 

12 

4-2 

506 

12 

39 

463 

12 

36 

431 

18 

4-4 

56-4 

13 

41 

53  3 

13 

3 8 

48-8 

13 

3*5 

45  4 

14 

4 2 

59  4 

14 

4-0 

55-8 

14 

3*7 

511 

14 

3 4 

47-5 

15 

4-2 

62  3 

15 

3 9 

58  5 

15 

3 6 

53  6 

15 

3*3 

49-8 

16 

44 

65-0 

16 

3-8 

611 

16 

3 5 

56  0 

16 

3 3 

53  0 

17 

4-0 

67-8 

17 

3*7 

63-6 

17 

3-4 

58  3 

17 

3 2 

54  2 

18 

8 9 

70-4 

18 

3 7 

661 

18 

3*4 

60  5 

18 

31 

56  3 

19 

3*8 

74*3 

19 

36 

68-6 

19 

3 3 

62-8 

19 

31 

58*4 

I by  far  prefer  using  this  Table  to  employing  the  method  generally  fol- 
lowed of  ascertaining  the  completion  of  the  washing-process  by  evapora- 
ting a quantity  of  the  filtrate  on  platinum-foil,  since  in  the  latter  case  it 
is  only  possible  to  obtain  an  infallible  proof  when  we  have  to  deal  with 
a precipitate  possessing  an  extremely  high  degree  of  insolubility ; if  the 
precipitate  be  soluble  to  any  marked  extent,  the  result  is  completely 
illusory. 

In  the  process  of  filtration  as  hitherto  conducted,  the  time  required 
is  so  long  and  the  quantity  of  wash-water  needed  so  great  that  some 
simplification  of  this  continually  recurring  operation  is  in  the  highest  de- 
gree desirable.  The  following  method,  which  depends  not  upon  the  remo- 
val of  the  impurity  by  simple  attenuation,  but  upon  its  displacement  by 


* 53,  a.] 


bunsen’s  method  of  rapid  filtration. 


69 


forcing  the  wash-water  through  the  precipitate,  appears  to  me  to  combine 
all  the  requisite  conditions  and  therefore  to  satisfy  the  need. 

The  rapidity  with  which  a liquid  filters  depends,  cceteris  paribus , upon 
the  difference  which  exists  between  the  pressure  upon  its  upper  and  lower 
surfaces.  Supposing  the  filter  to  consist  of  a solid  substance,  the 
pores  of  which  suffer  no  alteration  by  pressure  or  by  any  other  influence, 
then  the  volume  of  liquid  filtered  in  the  unit  of  time  is  nearly  propor- 
tional to  the  difference  in  pressure : this  is  clearly  shown  by  the  following 
experiments,  made  with  pure  water  and  a filter  consisting  of  a thin 
plate  of  artificial  pumice-stone.  The  thin  plate  of  pumice  was  hermeti- 
cally fastened  into  a funnel  consisting  of  a graduated  cylindrical  glass 
vessel,  the  lower  end  of  which  was  connected  with  a large  thick  flask 
by  means  of  a tightly  fitting  caoutchouc  cork.  The  pressure  in  the  flask 
was  then  reduced  by  rarefying  the  air  by  means  of  a method  to  be 
described  upon  another  occasion  ; and  for  each  difference  of  pressure  p, 
measured  by  a mercury  column,  the  number  of  seconds  t was  observed 
which  a given  quantity  of  water  occupied  in  passing  through  the  filter. 
The  following  are  the  results; — 


I. 


p. 

metre. 

t. 

pt. 

0*179 

91*7 

16*4 

0*190 

81*0 

15*4 

0*282 

52*9 

14*9 

0*472 

33*0 

15*6 

In  the  ordinary  process  of  filtration,  p on  the  average  amounts  to  no 
more  than  0*004  to  0*008  metre.  The  advantage  gained,  therefore,  is 
easily  perceived  when  we  can  succeed  by  some  simple,  practicable,  and 
easily  attainable  method  in  multiplying  this  difference  in  pressure  one  or 
two  hundred  times,  or,  say,  to  an  entire  atmosphere,  without  running  any 
risk  of  breaking  the  filter.  The  solution  of  this  problem  is  very  easy  : 
an  ordinary  glass  funnel  has  only  to  be  so  arranged  that  the  filter  can 
be  completely  adjusted  to  its  side  even  to  the  very  apex  of  the  cone. 
For  this  purpose  a glass  funnel  is  chosen  possessing  an  angle  of  60°, 
or  as  nearly  60°  as  possible,  the  walls  of  which  must  be  completely 
free  from  inequalities  of  every  description  ; and  into  it  is  placed  a second 
funnel  made  of  exceedingly  thin  platinum-foil,  and  the  sides  of  which 
possess  exactly  the  same  inclination  as  those  of  the  glass  funnel.  An 
ordinary  paper  filter  is  then  introduced  into  this  compound  funnel  in  the 
usual  manner ; when  carefully  moistened  and  so  adjusted  that  no  air- 
bubbles  are  visible  between  it  and  the  glass,  this  filter,  when  filled  with 
a liquid,  will  support  the  pressure  of  an  extra  atmosphere  without  ever 
breaking. 

The  platinum  funnel  is  easily  made  from  thin  platinum-foil  in  the 
following  manner  ; — In  the  carefully  chosen  glass  funnel  is  placed  a per- 
fectly accurately  fitting  filter  made  of  writing-paper ; this  is  kept  in 
position  by  dropping  a little  melted  sealing-wax  between  its  upper  edge 
and  the  glass ; the  paper  is  next  saturated  with  oil  and  filled  with  liquid 
plaster  of  Paris,  and  before  the  mixture  solidifies  a small  wooden  handle 
is  placed  in  the  centre.  After  an  hour  or  so  the  plaster  cone  with  the 
adhering  paper  filter  can  be  withdrawn  by  means  of  the  handle  from  the 


70 


OPERATIONS. 


funnel,  to  which  it  accurately  corresponds.  The  paper  on  the  outside 
of  the  cone  is  again  covered  with  oil,  and  the  whole  carefully  inserted 
into  liquid  plaster  of  Paris  contained  in  a small  crucible  4 or  5 centims. 
in  height.  After  the  mixture  has  solidified,  the  cone  may  be  easily  with- 
drawn ; the  adhering  paper  filter  is  then  detached,  and  any  small  pieces 
of  paper  still  remaining  removed  by  gently  rubbing  with  the  finger.  In 
this  manner  a solid  cone  is  obtained  accurately  fitting  into  a hollow  cone, 
and  of  which  the  angle  of  inclination  perfectly  corresponds  with  that  of 
the  glass  funnel. 


4- 


Fig.  43, 1,  represents  the  cones.  By  their  help  the  small  platinum  fun- 
nel is  made.  A piece  of  platinum  (shown  three-fourths 
of  the  natural  size  in  fig.  44)*  is  cut  from  foil  of  such  a 
thickness  that  one  square  centimetre  weighs  about  0T54 
grm.,  and  from  the  centre  a a vertical  incision  is  made 
by  the  scissors  to  the  edge  c b d.  The  small  piece  of 
foil  is  next  rendered  pliable  by  being  heated  to  redness, 
and  is  placed  upon  the  solid  cone  in  such  a manner 


* The  diameter  of  a in  the  original  drawing  is  2 '5  centimetres. 

/J/7 


bunsen’s  method  of  rapid  filtration. 


71 


§ 53,  a.] 

that  its  centre  a touches  the  apex  of  the  latter;  the  sides  a b d are 
then  closely  pressed  upon  the  plaster,  and  the  remaining  portion  of 
the  platinum  wrapped  as  equally  and  as  closely  as  possible  around  the 
cone.  On  again  heating  the  foil  to  redness,  pressing  it  once  more 
upon  the  cone,  and  inserting  the  whole  into  the  hollow  cone,  and 
turning  it  round  once  or  twice  under  a gentle  pressure,  the  proper 
shape  is  completed.  The  platinum  funnel,  which  should  not  allow  of 
the  transmission  of  light  through  its  extreme  point,  even  now  possesses 
such  stability  that  it  may  be  immediately  employed  for  any  purpose.  If 
desired,  it  may  be  made  still  stronger  by  soldering  down  the  overlap- 
ping portion  in  one  spot  only  to  the  upper  edge  of  the  foil  by  means  of 
a grain  or  two  of  gold  and  borax ; in  general,  however,  this  precaution 
is  unnecessary.  If  the  shape  has  in  any  degree  altered  during  this  latter 
process,  it  is  simply  necessary  to  drop  the  platinum  funnel  into  the  hol- 
low cone  and  then  to  insert  the  solid  cone,  when  by  one  or  two  turns 
of  the  latter  the  proper  form  may  be  immediately  restored.  The  plati- 
num funnel  is  placed  in  the  bottom  of  the  glass  funnel,  the  dry  paper 
filter  then  introduced  in  the  ordinary  manner,  moistened,  and  freed 
from  all  adhering  air-bubbles  by  pressure  with  the  finger.  A filter  so 
arranged  and  in  perfect  contact  with  the  glass,  when  filled  with  a liquid 
will  support  the  pressure  of  an  entire  atmosphere  without  the  least  dan- 
ger of  breaking ; and  the  interspace  between  the  folds  of  the  platinum- 
foil  is  perfectly  sufficient  to  allow  of  the  passage  of  a continuous  stream 
of  water. 

In  order  to  be  able  to  produce  the  additional  pressure  of  an  atmo- 
sphere, the  filtered  liquid  is  received  in  a strong  glass  flask  instead  of 
in  beakers.*  This  flask  is  closed  by  means  of  a doubly  perforated 
caoutchouc  cork,  through  one  of  the  holes  of  which  the  neck  of  the  glass 
funnel  is  passed  to  a depth  of  from  5 to  8 centimetres  (fig.  43,  k)  ; 
through  the  other  is  fitted  a narrow  tube  open  at  both  ends,  the  lower 
end  of  which  is  brought  exactly  to  the  level  of  the  lower  surface  of  the 
cork , to  the  other  is  adapted  the  caoutchouc  tube  connected  with  the 
apparatus  destined  to  produce  the  requisite  difference  in  pressure : this 
apparatus  will  be  described  immediately.  The  flasks  are  placed  in  a 
metallic  or  porcelain  vessel,  in  the  conical  contraction  of  which  several 
strips  of  cloth  are  fastened.  This  method  of  supporting  the  flask  has 
the  advantage  that,  in  one  and  the  same  vessel,  flasks  varying  in  size  from 
O' 5 to  2 '5  litres  stand  equally  well,  and  that  by  simply  laying  a cloth  over 
the  mouth  of  the  vessel,  the  consequences  of  an  explosion  (which  through 
inexperience  or  carelessness  is  possible)  are  rendered  harmless. 

It  is  impossible  to  employ  any  of  the  air-pumps  at  present  in  use  to  create 
the  difference  in  pressure,  since  the  filtrate  not  unfrequently  contains  chlo- 
rine, sulphurous  acid,  hydric  sulphide,  and  other  substances  which  would 
act  injuriously  upon  the  metallic  portions  of  these  instruments.  I there- 
fore employ  a water  air-pump  constructed  on  the  principle  of  Sprengel’s 
mercury-pump,  and  which  appears  to  me  preferable  to  all  other  forms  of 
air-pump  for  chemical  purposes,  since  it  effects  a rarefaction  to  within  6 
or  12  millimetres  pressure  of  mercury. 

Fig.  43  shows  the  arrangement  of  this  pump.  On  opening  the  pinch- 
cock  a,  water  flows  from  the  tube  l into  the  enlarged  glass  vessel  b , and 


* These  flasks  must  be  somewhat  thicker  than  those  ordinarily  used,  in  order 
to  prevent  the  possibility  of  their  giving  way  under  the  atmospheric  pressure. 


72 


OPERATIONS. 


[§  53,  a. 


thence  down  the  leaden  pipe  c.  This  pipe  has  a diameter  of  about  8 
millims.,  and  extends  downward  to  a depth  of  30  or  40  feet,  and  ends  in 
a sewer  or  other  arrangement  serving  to  convey  the  water  away.  The 
lower  end  of  the  tube  d possesses  a narrow  opening ; it  is  hermetically 
sealed  into  the  wider  tube  b , and  reaches  nearly  to  the  bottom  of  the 
latter.  A manometer  is  attached  to  the  upper  continuation  of  this  tube 
d by  means  of  a side  tube  at  dl ; at  e/2  is  attached  a strong  thick 
caoutchouc  tube  possessing  an  internal  diameter  of  5 millims.  and  an 
external  diameter  of  1 2 millims. ; this  leads  to  the  flask  which  is  to  be 
rendered  vacuous,  and  is  connected  with  it  by  means  of  the  short  nar- 
rowed tube  k.  Between  the  air-pump  and  the  flask  is  placed  the  small 
thick  glass  vessel  f,  in  which,  when  one  washes  with  hot  water,  the 
steam  which  may  be  carried  over  is  condensed.  All  the  caoutchouc 
joinings  are  made  with  very  thick  tubing,  the  internal  diameter  of 
which  amounts  to  about  5 millims.,  the  external  diameter  to  about  17 
millims.  The  entire  arrangement  is  screwed  down  upon  a board  fastened 
to  the  wall,  in  such  a manner  that  each  separate  piece  of  the  apparatus 
is  held  by  a single  fastening  only,  in  order  to  prevent  the  tubes  being 
strained  and  broken  by  the  possible  warping  of  the  board.  On  releasing 
the  pinchcock  a,  water  flows  from  the  conduit  l down  the  tube  c to  a 
depth  of  more  than  30  feet,  carrying  with  it  the  air  which  it  sucks 
through  the  small  opening  of  the  tube  d in  the  form  of  a continuous 
stream  of  bubbles.  No  advantage  is  gained  by  increasing  the  rapidity 
of  the  flow,  since  the  friction  exerl  ed  by  the  water  upon  the  sides  of  the 
leaden  pipe  acts  directly  as  a counter-pressure,  and  a comparatively 
small  increase  in  the  rapidity  of  the  flow  is  accompanied  by  a great  in- 
crease in  the  amount  of  this  friction.  Accordingly  at  g is  a second 
pinchcock,  by  which  the  stream  can  be  once  for  all  so  regulated  that,  on 
completely  opening  the  cock  <%,  the  friction,  on  account  of  the  dimin- 
ished rate  of  flow,  is  rendered  sufficiently  small  to  allow  of  the  maxi- 
mum degree  of  rarefaction.  Such  an  apparatus,  when  properly  regu- 
lated once  for  all  by  means  of  the  cock  g , exhausts  in  a comparatively 
short  time  the  largest  vessels  to  within  a pressure  of  mercury  equal  to 
the  tension  of  aqueous  vapor  at  the  temperature  possessed  by  the 
stream.*  The  tension  exerted  by  the  water-stream  in  my  laboratory,  in 
which  six  of  these  pumps  are  used,  amounts  to  about  7 millims.  in  win- 
ter and  10  millims.  in  summer.  The  filtration  is  made  in  the  following 
manner : The  flask  standing  in  the  metallic  or  porcelain  vessel  is  con- 

nected by  means  of  the  slightly  drawn-out  tube  k with  the  caoutchouc 
tube  h attached  to  the  pump,  the  cock  a having  been  previously  opened 
and  the  properly  fitted  moistened  filter  filled  with  the  liquid  to  be  fil- 
tered. As  usual,  the  clear  supernatant  fluid  is  first  poured  upon  the 
filter ; in  a moment  or  two  the  filtrate  runs  through  in  a continuous 
stream,  often  so  rapidly  that  one  must  hasten  to  keep  up  the  supply  of 
liquid,  since  it  is  advisable  to  maintain  the  filter  as  full  as  possible. 
After  the  precipitate  has  been  entirely  transferred,  the  filtrate  passes 
through  drop  by  drop,  and  the  manometer  not  unfrequently  now  shows 
a pressure  of  an  extra  atmosphere.  The  filter  may  be  filled  (in  fact 
this  is  to  be  recommended)  with  the  precipitate  to  within  a millimetre 


* The  time  required  to  obtain  the  above  degree  of  exhaustion  in  a flask  of 
from  1 to  3 litres  capacity  ranges  from  six  to  ten  minutes  ; the  quantity  of  water 
necessary  amounts  to  about  40  or  50  litres. 


bunsen’s  method  of  rapid  filtration. 


73 


§ 53,  a.] 

of  its  edge,  since  the  precipitate,  in  consequence  of  the  high  pressure  to 
which  it  is  subjected,  becomes  squeezed  into  a thin  layer  broken  up  by 
innumerable  fissures.  As  soon  as  the  liquid  has  passed  through  and  the 
first  traces  of  this  breaking  up  become  evident,  the  precipitate  will  be 
found  to  have  been  so  firmly  pressed  upon  the  paper,  that  on  cautiously 
pouring  water  over  it  it  remains  completely  undisturbed.  The  washing 
is  effected  by  carefully  pouring  water  down  the  side  of  the  funnel  to 
within  a centimetre  above  the  rim  of  the  filter:  the  washing  flask  for 
this  purpose  is  not  applicable  ; the  water  must  be  poured  from  an  open 
vessel.  After  the  filter  has  in  this  manner  been  replenished  four  times 
with  water  and  allowed  to  drain  for  a few  minutes,  it  will  be  found  to 
be  already  so  far  dried,  in  consequence  of  the  high  pressure  to  which  it 
has  been  subjected,  that  without  any  further  desiccation  it  may  be  with- 
drawn, together  with  the  precipitate,  from  the  funnel,  and  immediately 
ignited,  with  the  precautions  to  be  presently  given,  in  the  crucible. 

If  the  porosity  of  a paper  filter  containing  a precipitate  were  as  un- 
alterable as  that  of  a pumice-stone  filter,  the  experiments  above  de- 
scribed would  show  that  the  times  required  for  filtration,  according  to 
the  old  method  on  the  one  hand,  and  the  new  one  on  the  other,  would 
be  inversely  proportional  to  the  difference  in  pressure  in  each  case  ; that 
is,  by  using  the  pump  under  the  full  pressure  of  about  7 40  millims.,  the 
time  needed  to  wash  a precipitate,  occupying  by  the  old  process  an 
hour,  would  at  the  utmost  not  amount  to  more  than  30  seconds. 
In  using  such  pumice  filters*  to  drain  crystals  from  adhering  mother 
liquors,  or,  say,  to  wash  crystals  of  chromic  acid  by  means  of  concentra- 
ted sulphuric  acid  and  fuming  nitric  acid,  the  time  occupied  in  the  filtra- 
tion is  scarcely  longer  than  that  needed  to  pour  a liquid  slowly  from  one 
vessel  to  another.  In  filtering  by  means  of  paper,  the  precipitate  gra- 
dually closes  up  the  pores  of  the  filter,  and  accordingly  such  an  extra- 
ordinary acceleration  as  this  can  no  longer  be  expected.  But  the  fol- 
lowing examples  will  show  the  saving  of  time  and  labor  the  method 
effects,  even  under  all  unfavorable  conditions.  For  these  experiments 
I have  purposely  chosen  the  hydrated  chromium  sesquioxide,  since 
it  is  one  of  the  most  difficult  of  precipitates  to  wash  thoroughly. 
A solution  of  chromium  chloride  was  prepared  by  acting  with  fuming 
hydrochloric  acid  upon  potassium  dichromate  ; and  by  means  of  a mea- 
suring-vessel, which  allowed  the  amount  of  chromium  to  be  estimated  to 
within  O'OOOl  grm.,  successive  portions  of  the  liquid  were  withdrawn, 
and  the  chromium  oxide  contained  in  them  precipitated  with  the  usual 
precautions  by  ammonia.  The  volume  of  liquid,  the  quantity  of  am- 
monia employed,  the  time  occupied  in  boiling  and  in  permitting  the  pre- 
cipitate to  settle,  the  angle  of  inclination  possessed  by  the  funnel,  and 
the  size  of  the  filter  were  the  same  in  all  the  experiments.  All  the  pre- 
cipitates were  washed  with  hot  water,  and,  after  burning  the  filter,  igni- 
ted over  a blast-lamp  for  a few  minutes  ; in  weighing,  the  platinum 
crucible  was  tared  by  one  of  about  equal  weight,  and  the  position  of 
equilibrium  of  the  beam  determined  by  vibrations. 

I first  attempted  to  filter  one  of  the  precipitates  in  the  ordi- 
nary way.  amounted  to  2 ; and  consequently,  from  the  table,  8*4 
v 


* Am.  Jour.  Sci.,  xlvii.  p.  336. 


OPERATIONS. 


74 


[§  53,  a. 


fresh  additions  of  water  were  required  in  order  to  wash  the  precipitate 
to  the  Twin)  w Par^*  The  times  required  were  as  follows  : — 

In  transferring  the  precipitate  from  the  beaker  ) 40' 


and  allowing  it  to  drain [ 

For  the  first  addition  of  water  to  run  through,  48 
44  second  44  44  70 

“ third  “ “ 80 

Total  length  of  time 238 


At  this  point  the  experiment  was  discontinued,  as  the  filtrate  became 
turbid.  A second  experiment  failed  from  the  same  cause. 

Accordingly  I attempted  to  wash  the  precipitate  by  decantation. 
The  volume  of  the  precipitate  amounted  to  about  30  cub.  centims. ; 
the  quantity  of  water  required  to  fill  the  beaker  was  seven  times  the 

V 

volume  of  the  precipitate ; hence  — was  7,  and  the  requisite  number 

of  decantations  to  reduce  the  amount  of  impurity  to  the  -3-0  o~g“o  Par^  was 
5*2.  The  times  observed  were  as  follows : — 

IT. 


For  the  first  decantation  to  run  through  the  filter. ...  15' 


“ second  “ 44  44  12 

44  third  44  44  44  18 

44  fourth  44  44  44  15 

44  fifth  44  44  44  18 

In  transferring  the  precipitate  to  the  filter 30 


Time  required  in  washing 108 

Weight  of  the  precipitate 0*2458  grm. 

Volume  of  wash-water  n V .* 1050  cub.  centims. 


III. 

Experiment  repeated.  Number  of  decantations  7.  Other  circum- 
stances the  same  as  in  the  foregoing  determination. 

Time  required  in  washing 140' 

Weight  of  the  precipitate 0*2452  grm. 

Volume  of  wash- water 1200  cub.  centims. 

IV. 

After  ten  decantations. 

Time  required  in  washing 

Weight  of  the  precipitate 

V olume  of  wash-water 

By  filtration  with  the  platinum  cone  and  the 
results  were  obtained  : — 


180' 

0*2443  grm. 

1750  cub.  centims. 
pump  the  follo  wing 


V. 


In 


transferring 
water)  . . , 


the  precipitate  to  the  filter  (17  cub.  centims.  ) g, 


53,  a.] 


RUNSEn’s  METHOD  OF  RAPID  FILTRATION. 


75 


For  the  first  addition  of  water  (25  cub.  cent.)  to  run  through,  2' 


“ second  “ “ “ 3 

“ third  “ “ “ 2 

££  fourth  (C  u “ 2 

“ fifth  “ “ “ 2 

In  draining  the  precipitate 2 

Time  required 19 

Weight  of  precipitate 0*2435  grm. 

Volume  of  wash-water 142  cub.  centims. 

Pressure  of  manometer 0*576  metre. 


VI. 

In  transferring  the  precipitate  and  allowing  the  water  (18  cub.  cen- 
tims.) to  run  through 

For  the  first  addition  of  water  (25  cub.  cent.)  to  run  through 


“ second  “ ££  ££  ££  5 

“ third  “ “ “ ££  5 

££  fourth  ££  ££  ££  ££  5 

In  draining  the  precipitate 1 

Time  required 28 


Weight  of  precipitate 0*2434  grm. 

Volume  of  wash-water 118  cub.  centims. 

Pressure 0*600  metre. 


VII. 

In  transferring  the  precipitate  and  allowing  the  water  (20  cub. 


centims.)  to  run  through j 

For  the  first  addition  of  water  (25  cub.  cent.)  to  run  through 3 

££  v second  ££  ££  ££  ££  3 

££  third  ££  ££  “ ££  3 

In  draining  the  precipitate 3 

Time  required 16 


Weight  of  precipitate 0*2432  grm. 

Volume  of  wash- water 95  cub.  centims. 

Pressure 0*584  metre. 

VIII. 


In  transferring  with  25  cub.  centims.  of  water 8 

For  the  first  addition  of  25  cub.  centims.  to  run  through 5 

For  the  second  addition  of  25  cub.  centims.  to  run  through 5 

In  draining  the  precipitate 3 

Time  required 21 


Weight  of  precipitate 0*2435  grm. 

Volume  of  wash- water 72  cub.  centims. 

Pressure 0*593  metre. 


76 


OPERATIONS. 


IX. 


In  transferring  with  1 5 cub.  centims.  of  water  and  allowing  it  to 

run  through 

For  a single  addition  to  run  through 

In  draining  the  precipitate 


Time  required 

Weight  of  precipitate 
Volume  of  wash- water 

Pressure 


12 

0-2439  grm. 

41  cub.  centims. 

0*572  metre. 


X. 

In  transferring  the  precipitate  with  13  cub.  centims.  of  water 5' 

For  a single  addition  of  water  (26  cub.  cent.)  to  run  through 8 

In  draining  the  precipitate 1 


Time  required .... 

Weight  of  precipitate, 
Volume  of  wash- water 
Pressure 


14 

0-2439  grm. 

39  cub.  centims. 

0*530  metre. 


In  washing,  by  means  of  decantation,  in  the  ordinary  manner,  the 
amounts  of  chromium  sesquioxide  found  were  as  follows  : — 

grm. 

II.  0*2458,  after  5 decantations,  washed  to  the  -g  0 j,  0 0 part. 

HI.  0-2452  “ 7 “ “ *W<mr  part. 

IV.  0-2443  “10  « “ two  lutt  E Part. 


0*2451  mean. 

By  the  use  of  the  pump : — 


grm. 

V.  0*2435,  after 

VI.  0*2434  “ 

VII.  0*2432  “ 

VIII.  0*2435  “ 

IX.  0*2439  “ 

X.  0*2439  “ 


5 additions  of  water. 

4 « cc 

3 “ “ 

2 “ “ 

1 addition  of  water. 
1 « a 


0*2436  mean. 

Hence  the  probable  amount  of  chromium  sesquioxide  contained  in  the 
solution,  according  to  the  experiments  with  the  pump,  was  0*2436  grm. : 
according  to  the  old  method  of  decantation  it  was  somewhat  higher, 
namely  0*2451  grm.  This  excess  of  1*5  milligramme  shows  that  the  adhe- 
sion of  the  soluble  matters  to  the  precipitate  and  to  the  filter  is,  in 
consequence  of  the  greater  pressure,  more  easily  overcome  in  the  new 
method  than  in  the  customary  process ; it  follows,  therefore,  that  we  can 
obtain  a more  complete  washing  by  the  new  method  than  by  the  old. 
The  old  process  of  decantation  required  108  minutes  and  1050  cub.  cen- 
tims. of  water  to  effect  a washing  to  the  g6}0-0-  part ; the  new,  on  the 
contrary,  only  12  to  14  minutes,  and  not  more  than  39  to  41  cub.  cen- 
tims. of  wash-water. 


53,  b,  c.] 


ADVANTAGES  OF  BUNSEN’S  NEW  METHOD. 


77 


§ 53,  b. 

Bunsen’s  Method  of  Drying  and  Igniting  Precipitates. 

If  a precipitate  be  heated  in  a platinum  crucible  immediately  after 
filtration  by  the  older  process,  a portion  will  inevitably  be  projected  out 
of  the  crucible.  Hitherto,  therefore,  it  has  been  necessary  to  dry  the  filtei 
and  precipitate  before  ignition.  Now  to  dry  a quantity  of  hydrated 
chromium  sesquioxide  containing  0*2436  grm.  Cr203  in  a water-bath  at 
100°  C.  requires  at  least  five  hours ; and,  moreover,  bringing  the  dried 
precipitate  into  the  crucible,  burning  the  filter,  and  gradually  igniting 
the  mass  is  in  the  highest  degree  tedious  and  troublesome.  All  this  ex- 
penditure of  time  and  labor  may  be  saved  by  employing  the  new  method. 
By  its  means  a precipitate  is  as  completely  dried  upon  the  filter  in  from  1 
to  5 minutes  as  if  it  had  been  exposed  from  5 to  8 hours  in  a drying-cham- 
ber; and  it  can  immediately,  filter  and  all,  be  thrown  into  a platinum  or 
porcelain  crucible  and  ignited  without  the  slightest  fear  of  its  spurting. 
By  operating  in  the  following  manner  the  filter  burns  quietly  without 
flame  or  smoke  ; this  phenomenon,  although  remarkable,  easily  admits  of 
an  explanation.  The  portion  of  filter-paper  free  from  precipitate  is 
tightly  wrapped  round  the  remainder  of  the  filter  in  such  a manner  that 
the  precipitate  is  enveloped  in  from  four  to  six  folds  of  clean  paper. 
The  whole  is  then  dropped  into  the  platinum  or  porcelain  crucible  lying 
obliquely  upon  a triangle  over  the  lamp,  and  pushed  down  against  its 
sides  with  the  finger.  The  cover  is  then  supported  against  the  mouth 
of  the  crucible  in  the  ordinary  way,  and  the  ignition  commenced  by 
heating  the  portion  of  the  crucible  in  contact  with  the  cover.  When 
the  flame  has  the  proper  size  and  position,  the  filter  carbonizes  quietly 
without  any  appearance  of  flame  or  considerable  amount  of  smoke. 
When  the  carbonization  proceeds  too  slowly,  the  flame  is  moved  a little 
toward  the  bottom  of  the  crucible.  After  some  time  the  precipitate 
appears  to  be  surrounded  only  by  an  extremely  thin  envelope  of  carbon, 
possessing  exactly  the  form  (of  course  diminished  in  size)  of  the  original 
filter;  the  flame  is  then  increased,  and  the  crucible  maintained  at  a 
bright-red  heat  until  the  carbon  contained  in  this  envelope  is  consumed. 
The  combustion  proceeds  so  quietly  that  the  resulting  ash  surrounding 
the  precipitate  possesses,  even  to  the  smallest  fold,  the  exact  form  of 
the  original  filter.  If  the  ash  shows  here  and  there  a dark  color,  it  is  sim- 
ply necessary  to  heat  the  crucible  over  a blast-lam})  for  a few  minutes 
to  effect  the  complete  removal  of  the  trace  of  carbon.  This  method  of 
burning  a filter  is  extremely  convenient  and  accurate  ; it  is  only  necessa- 
ry to  give  a little  attention  at  first  to  the  slow  carbonization  of  the  paper, 
after  which  the  further  progress  of  the  operation  may  be  left  to  itself. 

Gelatinous,  finely  divided,  granular,  and  crystalline  precipitates,  such 
as  alumina,  calcium  oxalate,  barium  sulphate,  silica,  magnesium  ammo- 
nium phosphate,  &c.,  may  with  equal  facility  be  treated  in  this  manner ; 
so  that  even  in  this  particular  the  work,  in  comparison  with  the  method 
generally  adopted,  is  considerably  shortened  and  simplified. 

§ 53,  c. 

Advantages  of  Bunsen’s  New  Method. 

From  the  above  experiments  it  appears  that  the  time  necessary  to 
filter  and  dry  a quantity  of  chromium  sesquioxyd,  hitherto  requiring 


78 


OPERATIONS. 


about  7 hours,  is  reduced  by  the  new  method  to  13  minutes.  This  sav- 
ing of  time  is,  moreover,  proportionately  greater  in  the  case  of  precipi- 
tates more  easily  filtered  than  hydrated  chromium  sesquioxide.  Parti- 
cularly is  this  so  in  separating  a finely  suspended  precipitate  from  a 
large  volume  of  water.  Under  these  circumstances  the  clear  fluid  runs 
through  the  filter  in  a continuous  stream,  so  rapidly  that  it  is  scarcely 
possible  to  maintain  the  supply ; the  entire  operation,  in  fact,  requires 
scarcely  more  time  than  that  necessary  to  pour  a liquid  from  one  vessel 
to  another.  Filtration,  therefore,  may  be  effected  as  quickly  through  the 
smallest  as  through  the  largest  filter.  Moreover,  the  exceedingly  small 
amount  of  water  required  to  wash  a precipitate  completely  renders  unne- 
cessary the  tedious  evaporations  which  by  the  older  method  are  almost 
inevitable  when  the  filtrate  is  needed  for  a further  separation.  Thus 
the  introduction  of  impurities  from  the  action  of  the  liquid  upon  the 
dish  in  the  course  of  evaporation  is  prevented  ; and  also  the  loss  due  to 
the  slight  solubility  of  the  greater  number  of  precipitates  in  the  wash- 
water  is  reduced  to  a minimum.  Supposing  we  had  to  analyze  an  alka- 
line chromate  in  which  the  quantity  of  chromic  acid  is  equivalent  to 
0*2436  grm.  chromic  sesquioxide,  as  in  the  above  described  experi- 
ments, then  to  determine  the  proportion  of  ^alkali,  we  should,  by  using 
the  older  method,  require  the  preliminary  evaporation  of  about  1050 
cub.  centims.  of  liquid  ; by  the  new  method  the  evaporation  of  40  cub. 
centims.  only  is  necessary.  Now  by  employing  the  water-bath,  with 
constant  water-level,  it  is  possible,  under  favorable  circumstances,  to 
evaporate  in  a porcelain  dish  1 cub.  centim.  of  water  in  27  seconds. 
Consequently  the  evaporation  of  the  filtrate  obtained  by  the  older 
method  would  occupy  about  eight  hours,  whilst  by  the  new  18  minutes 
only  are  required.  The  total  length  of  time  needed  to  filter  the  chro- 
mium sesquioxide,  wash  and  dry  the  precipitate,  and  evaporate  the 
filtrate  is  reduced,  therefore,  from  14  or  15  hours  to  about  32  minutes. 

Experience  has  shown  that,  on  the  average,  three  or  four  analyses  can 
now  be  made  in  the  time  formerly  demanded  by  a single  one. 

Another  and  an  inestimable  advantage  springs  from  the  peculiar  con- 
dition of  a precipitate  filtered  by  this  method.  It  not  unfrequently 
happens,  even  in  the  hands  of  experienced  manipulators,  in  conse- 
quence of  the  agitation  it  is  necessary  to  give  to  the  contents  of  the 
filter  to  effect  their  complete  washing,  that  the  surface  of  the  filter  be- 
comes injured  and  torn  so  that  the  precipitate  becomes  mixed  with  fila- 
ments of  paper  ; this  is  particularly  the  case  in  using  hot  water.  Suppos- 
ing the  precipitate  to  consist  of  mixed  hydrates  of  the  sesquioxides  (for 
example,  iron  and  alumina),  it  will  be  found  on  redissolving  in  an  acid, 
that  the  filaments,  like  tartaric  acid,  prevent  the  complete  separation 
of  these  substances  by  subsequent  precipitation  ; thus  the  alumina  will 
contain  iron,  and  on  precipitation  by  means  of  ammonium  sulphide  will 
be  colored  black.  On  the  other  hand,  by  employing  the  new  method 
the  precipitate  coheres  so  firmly  that  the  introduction  of  this  source  of 
error  is  impossible,  even  by  using  common  gray  filter-paper.  The  most 
gelatinous  precipitates,  as  hydrated  ferric  oxide,  alumina,  <fcc.,  adhere  to 
the  filter  in  a thin  coherent  layer,  and  may  be  removed,  piece  after 
piece,  so  completely  that  the  paper  remains  perfectly  clean  and  white. 
The  advantage  thus  gained  where  it  is  necessary  to  transfer  mixed  pre- 
cipitates to  another  vessel  in  order  to  effect  their  subsequent  separation 
is  evident. 


§ 53,  d.J 


bunsen’s  simplified  exhausting  apparatus. 


79 


Since  the  bulk  of  the  moist  precipitates,  particularly  that  of  the  more 
gelatinous,  is  so  much  diminished  under  the  high  pressure,  the  precipi- 
tate only  occupying  one-third  to  one-sixth  of  its  bulk  under  ordinary 
circumstances,  a filter  of  one-third  to  one-sixth  of  the  size  usually  em- 
ployed may  be  taken,  and  thus  the  amount  of  ash  proportionately  les- 
sened. 


§ 53,  d. 

Bunsen’s  Simplified  Exhausting  Apparatus. 

It  is  not  necessary  to  use  a pump  as  powerful  as  that  described,  since 
a fall  of  10  or  15  feet  is  sufficient  to  filter  a precipitate  according  to  the 
above  described  method,  and  so  far  to  dry  it 
that  it  can  be  immediately  ignited  in  the  cru- 
cible. The  simple  arrangement  represented  in 
fig.  45  answers  this  purpose.  It  consists  of  two 
equal-sized  bottles,  a and  a',  of  from  2 to  4 
litres  capacity,  each  of  which  is  provided  near 
the  bottom  with  a small  stopcock  designed  to 
regulate  the  flow  of  water.  Suppose  a filled 
with  water  and  placed  upon  a shelf  as  high 
above  the  ground  as  possible,  and  a!  placed 
empty  on  the  floor,  and  the  two  stopcocks  con- 
nected by  means  of  caoutchouc  tubing  c,  then 
on  allowing  water  to  flow  down  the  tube  the 
air  in  the  upper  bottle  becomes  somewhat 
rarefied  ; and  in  order  to  employ  the  conse- 
quent difference  in  pressure  (amounting  to  a 
column  of  mercury  about  0‘2  metre  in  height) 
for  the  purpose  of  filtration,  it  is  only  neces- 
sary to  connect  the  mouth  of  the  upper  bottle 
with  the  tube  of  the  filter-flask.  When  the 
water  has  ceased  to  flow,  the  position  of  the 
bottle  is  reversed,  when  the  operation  recom- 
mences. So  small  a pressure  as  0*2  metre 
suffices  to  render  the  filter  and  its  contents  so 
far  dry  that  they  may  be  immediately  with- 
drawn from  the  funnel  and  ignited  without  any 
other  preliminary  desiccation.  The  following 
experiment,  made  with  a portion  of  the  same 
solution  of  chromium  used  in  the  former  deter- 
minations, will  serve  to  show  the  saving  of 
time  effected  by  this  simple  arrangement : — 


XI. 


Transferring  the  precipitate  with  14 ) 

cub.  centims.  of  water j 

For  a single  addition  of  26  cub.  centims.  [ 

of  wash-water  to  run  through j 

To  drain  the  precipitate 4 


Time  required  in  washing 


25 


80 


OPERATIONS, 


[§  54. 


Weight  of  the  precipitate 0*2435  grm. 

Volume  of  wash-water 40  cub.  centims. 

Pressure  in  manometer 0*184  metre. 


This  amount  of  chromium  sesquioxide  (0*2435  grm.)  differs  from  the 
• mean  of  the  former  experiments  (0*2436  grm.)  by  one-tenth  of  a milli- 
gramme only,  and  shows  that  even  by  a pressure  of  0*184  metre  the  wash- 
ing is  as  complete  by  the  single  addition  of  26  cub.  centims.  of  water. 
The  duration  of  the  filtering  process  in  the  former  experiments  ranged 
from  12  to  14  minutes  under  a difference  of  pressure  amounting  to  from 
0*53  to  0*572  metre;  in  the  last  experiment  it  required  25  minutes 
under  a pressure  of  0*184  metre,  or  about  double  the  length  of  time. 
The  time  needed  to  analyze  potassium  chromate  in  the  former  case  was 
reduced  from  14  hours  to  32  minutes;  by  the  latter  method  the  reduc- 
tion would  be  from  14  hours  to  44  minutes. 

§ 54. 

5.  Analysis  by  Measure  (Volumetric  Analysis). 

The  principle  of  volumetric  analysis  has  been  explained  already  in  the 
“ Introduction,”  where  we  have  seen  how  the  quantity  of  protoxide  of 
iron  present  in  a fluid  may  be  determined  by  means  of  a solution  of 
permanganate  of  potassa,  the  value  of  which  has  been  previously  ascer- 
tained by  observing  the  quantity  required  to  oxidize  a known  amount 
of  protoxide  of  iron. 

In  order  to  make  the  matter  as  clear  as  possible  I will  here  adduce  a 
few  more  examples. 

Suppose  we  have  prepared  a solution  of  chloride  of  sodium  of  such  a 
strength  that  100  c.  c.  will  exactly  precipitate  1 grm.  silver  from  its 
solution  in  nitric  acid,  we  can  use  it  to  estimate  unknown  quantities  of 
silver.  Let  us  imagine,  for  instance,  we  have  an  alloy  of  silver  and 
copper  in  unknown  proportion,  we  dissolve  1 grm.  in  nitric  acid,  and 
add  to  the  solution  our  solution  of  chloride  of  sodium,  drop  by  drop, 
until  the  whole  of  the  silver  is  thrown  down,  and  an  additional  drop 
fails  to  produce  a further  precipitate.  The  amount  of  silver  present 
may  now  be  calculated  from  the  amount  of  solution  of  chloride  of 
sodium  used.  Thus,  supposing  we  have  used  80  c.  c.,  the  amount  of 
silver  present  in  the  alloy  is  80  per  cent. ; since,  as  100  c.  c.  of  the  solu- 
tion of  chloride  of  sodium  will  throw  down  1 grm.  of  pure  silver  ( i.e . 
of  100  per  cent.),  it  follows  that  every  c.  c.  of  the  chloride  of  sodium 
solution  corresponds  to  1 per  cent,  of  silver. 

Another  example.  It  is  well  known  that  iodine  and  sulphuretted  hydro- 
gen cannot  exist  together : whenever  these  two  substances  are  brought 
in  contact,  decomposition  immediately  ensues,  the  hydrogen  separating 
from  the  sulphur  and  combining  with  the  iodine  (1  + HS  = HI  -j-  S). 
Hydriodic  acid  exercises  no  action  on  starch-paste,  whereas  the  least 
trace  of  free  iodine  colors  it  blue.  How,  if  we  prepare  a solution  of 
iodine  (in  iodide  of  potassium)  containing  in  100  c.  c.  0*7470  grm.  iodine, 
we  may  with  this  decompose  exactly  0*1  grm.  sulphuretted  hydrogen, 
for  17  : 127  : : 0*1  : 0*7470.  Let  us  suppose,  then,  we  have  before  us  a 
fluid  containing  an  unknown  amount  of  sulphuretted  hydrogen,  which 
it  is  our  intention  to  determine.  We  add  to  it  a little  starch-paste,  and 
then,  drop  by  drop,  our  solution  of  iodine,  until  a persistent  blue  colo- 


54.] 


VOLUMETRIC  ANALYSIS. 


81 


ration  of  the  fluid  indicates  the  formation  of  iodide  of  starch,  and  hence 
the  complete  decomposition  of  the  sulphuretted  hydrogen.  The  amount 
of  the  latter  originally  present  in  the  fluid  may  now  be  readily  calculated 
from  the  amount  of  solution  of  iodine  used.  Say,  for  instance,  we  have 
used  50  c.  c.  of  iodine  solution,  the  fluid  contained  originally  0*05  sul- 
phuretted hydrogen;  since,  as  we  have  seen,  100  c.  c.  of  our  iodine 
solution  will  decompose  exactly  0*1  grm.  of  that  body. 

Solutions  of  accurately  known  composition  or  strength,  used  for  the 
purposes  of  volumetric  analysis,  are  called  standard  solutions.  They 
may  be  prepared  in  two  ways,  viz.,  (a)  by  dissolving  a weighed  quantity 
of  a substance  in  a definite  volume  of  fluid  ; or  (6),  by  first  preparing  a 
suitably  concentrated  solution  of  the  reagent  required,  and  then  deter- 
mining its  exact  strength  by  a series  of  experiments  made  with  it  upon 
weighed  quantities  of  the  body  for  the  determination  of  which  it  is  in- 
tended to  be  used. 

In  the  preparation  of  standard  solutions  by  method  a,  a certain  defi- 
nite strength  is  adopted  once  for  all,  which  is  usually  based  u]jon  the 
principle  of  an  exact  correspondence  between  the  number  of  grammes 
of  the  reagent  contained  in  a litre  of  the  fluid,  and  the  equivalent  num- 
ber of  the  reagent  (H=l).  In  the  case  of  standard  solutions  prepared 
by  method  6,  this  may  also  be  easily  done,  by  diluting  to  the  required 
degree  the  still  somewhat  too  concentrated  solution,  after  having  accu- 
rately determined  its  strength  ; however,  as  a rule,  this  latter  process  is 
only  resorted  to  in  technical  analyses,  where  it  is  desirable  to  avoid  all 
calculation.  Fluids  which  contain  the  eq.  number  of  grammes  of  a sub- 
stance in  one  litre,  are  called  normal  solutions  ’ those  which  contain  yL 
of  this  quantity,  deoinormal  solutions. 

The  determination  of  a standard  solution  intended  to  be  used  for  vol- 
umetric analysis  is  obviously  a most  important  operation ; since  any 
error  in  this  will,  of  course,  necessarily  falsify  every  analysis  made  with 
it.  In  scientific  and  accurate  researches  it  is,  therefore,  always  advisa- 
ble, whenever  practicable,  to  examine  the  standard  solution — no  matter 
whether  prepared  by  method  a,  or  by  method  6,  with  subsequent  dilu- 
tion to  the  required  degree — by  experimenting  with  it  upon  accurately 
weighed  quantities  of  the  body  for  the  determination  of  which  it  is  to 
be  used. 

In  the  previous  remarks  I have  made  no  difference  between  fluids  of 
known  composition  and  those  of  known  power ; and  this  has  hitherto 
been  usual.  But  by  accepting  the  two  expressions  as  synonymous,  we 
take  for  granted  that  a fluid  exercises  a chemical  action  exactly  corre- 
sponding to  the  amount  of  dissolved  substance  it  contains — that,  for  in- 
stance, a solution  of  chloride  of  sodium  containing  1 eq.  Na  Cl  will  pre- 
cipitate exactly  1 eq.  silver.  This  presumption,  however,  is  very  often 
not  absolutely  correct,  as  will  be  shown  with  reference  to  this  very  ex- 
ample, § 115,  b,  5.  In  such  cases,  of  course,  it  is  not  merely  advisable, 
but  even  absolutely  necessary,  to  determine  the  strength  of  the  fluid 
by  experiment,  although  the  amount  of  the  reagent  it  contains  may 
be  exactly  known,  for  the  power  of  the  fluid  can  be  inferred  from  its 
composition  only  approximately  and  not  with  perfect  exactness.  If  a 
standard  solution  keeps  unaltered,  this  is  a great  advantage,,  as  it  dis- 
penses with  the  necessity  of  determining  its  strength  before  every  fresh 
analysis. 

That  particular  change  in  the  fluid  operated  upon  by  means  of  a 

6 


82 


OPERATIONS. 


L§  M- 

standard  solution  which  marks  the  completion  of  the  intended  decom- 
position, is  termed  the  final  reaction.  This  consists  either  in  a 
change  of  color , as  is  the  case  when  a solution  of  permanganate  of 
potassa  acts  upon  an  acidified  solution  of  protoxide  of  iron,  or  a solu- 
tion of  iodine  upon  a solution  of  sulphuretted  hydrogen  mixed  with 
starch  paste;  or  in  the  cessation  of  the  formation  of  a precipitate  upon 
further  addition  of  the  standard  solution,  as  is  the  case  when  a stand- 
ard solution  of  chloride  of  sodium  is  used  to  precipitate  silver  from 
its  solution  in  nitric  acid  ; or  in  incipient  precipitation , as  is  the  case 
when  a standard  solution  of  silver  is  added  to  a solution  of  hydrocyanic 
acid  mixed  with  an  alkali ; or  in  a change  in  the  action  of  the  examined 
fluid  upon  a particular  reagent , as  is  the  case  when  a solution  of  arsen- 
ite  of  soda  is  added,  drop  by  drop,  to  a solution  of  chloride  of  lime, 
until  the  mixture  no  longer  imparts  a blue  tint  to  paper  moistened  with 
iodide  of  potassium  and  starch-paste,  &c. 

The  more  sensitive  a final  reaction  is,  and  the  more  readily,  posi- 
tively, and  rapidly  it  manifests  itself,  the  better  is  it  calculated  to  serve 
as  the  basis  of  a volumetric  method.  In  cases  where  it  is  an  object  of 
great  importance  to  ascertain  with  the  greatest  practicable  precision  the 
exact  moment  when  the  reaction  is  completed,  the  analyst  may  some- 
times prepare,  besides  the  actual  standard  solution,  another,  ten  times 
more  dilute,  and  use  the  latter  to  finish  the  process,  carried  nearly  to 
completion  with  the  former. 

But  a good  final  reaction  is  not  of  itself  sufficient  to  afford  a safe  basis 
for  a good  volumetric  method ; this  requires,  as  the  first  and  most  in- 
dispensable condition,  that  the  particular  decomposition  which  consti- 
tutes the  leading  point  of  the  analytical  process  should — at  least  under 
certain  known  circumstances — remain  unalterably  the  same.  Wherever 
this  is  not  the  case — where  the  action  varies  with  the  greater  or  less 
degree  of  concentration  of  the  fluid,  or  according  as  there  may  be  a little 
more  or  less  free  acid  present ; or  according  to  the  greater  or  less  rapid- 
ity of  action  of  the  standard  solution ; or  where  a precipitate  formed  in 
the  course  of  the  process  has  not  the  same  composition  throughout  the 
operation — the  basis  of  the  volumetric  method  is  fallacious,  and  the 
method  itself,  therefore,  of  no  value. 


SECTION  II. 


REAGENTS. 

§ 55. 

For  general  information  respecting  reagents,  I refer  the  student  to  my 
volume  on  “ Qualitative  Analysis.” 

The  instructions  given  here  will  be  confined  to  the  preparation,  testing, 
and  most  important  uses  of  those  chemical  substances  which  subserve 
principally  and  more  exclusively  the  purposes  of  quantitative  analysis. 
Those  reagents  which  are  employed  in  qualitative  investigations,  having 
been  treated  of  already  in  the  volume  on  the  qualitative  branch  of  the 
analytical  science,  will  therefore  be  simply  mentioned  here  by  name. 

The  reagents  used  in  quantitative  analysis  are  properly  arranged  under 
the  following  heads  : — 

A.  Reagents  for  gravimetric  analysis  in  the  wet  way. 

II.  Reagents  for  gravimetric  analysis  in  the  dry  way. 

C.  Reagents  for  volumetric  analysis. 

D.  Reagents  used  in  organic  analysis. 

The  mode  of  preparing  the  fluids  used  in  volumetric  analysis,  will  be 
found  where  we  shall  have  occasion  to  speak  of  their  application. 

A.  REAGENTS  FOR  GRAVIMETRIC  ANALYSIS 
IN  THE  WET  WAY. 

I.  SIMPLE  SOLVENTS. 

§ 56. 

1.  Distilled  Water  (see  “ Qual.  Anal.”). 

Water  intended  for  quantitative  investigations  must  be  perfectly  pure. 
Water  distilled  from  glass  vessels  leaves  a residue  upon  evaporation  in 
a platinum  vessel  (see  experiment  No.  5),  and  is  therefore  inapplicable 
for  many  purposes  ; as,  for  instance,  for  the  determination  of  the  exact 
degree  of  solubility  of  sparingly  soluble  substances.  For  certain  uses  it 
is  necessary  to  free  the  water  by  ebullition  from  atmospheric  air  and  car* 
bonic  acid. 

2.  Alcohol  (see  “ Qual.  Anal.”). 

a.  Absolute  alcohol,  b.  Rectified  spirit  of  wine  of  various  degrees  of 
strength. 

3.  Ether. 

The  application  of  ether  as  a solvent  is  very  limited.  It  is  more  fre- 
quently used  mixed  with  spirit  of  wine,  in  order  to  diminish  the  solvent 


84 


REAGENTS. 


power  of  the  latter  for  certain  substances,  e.g.y  bichloride  of  platinum 
and  chloride  of  ammonium.  The  ordinary  ether  of  the  shops  will  answer 
the  purpose. 

II.  ACIDS  AND  HALOGENS. 

a.  Oxygen  Acids. 

§57. 

1.  Sulphuric  Acid. 

a.  Concentrated  sulphuric  acid  of  the  shops. 

b.  Concentrated  pure  sulphuric  acid. 

c.  Dilute  sulphuric  acid. 

See  “ Qual.  Anal.” 

2.  Nitric  Acid. 

a.  Pure  nitric  acid  of  1*2  sp.  gr.  (see  “ Qual.  Anal.”). 

b.  Red  fuming  nitric  acid  (concentrated  nitric  acid  containing  some 
hyponitric  acid). 

Preparation. — Two  parts  of  pure,  dry  nitrate  of  potassa  are  introduced 
into  a capacious  retort,  and  one  part  of  concentrated  sulphuric  acid  is 
added  either  through  the  tubulure  of  the  retort,  or  if  a common  non- 
tubulated  one  is  used,  through  the  neck  by  means  of  a long  funnel-tube 
bent  at  the  lower  end,  carefully  avoiding  soiling  the  neck  of  the  retort. 
The  latter  being  put  into  a vessel  filled  with  sand,  or,  better  still,  with 
iron  turnings,  is  then  connected  with  a receiver,  but  not  quite  air-tight. 
The  distillation  is  conducted  at  a gradually  increased  heat,  and  carried 
to  dryness.  The  cooling  of  the  receiver  must  be  properly  attended  to 
during  the  distillation.  In  the  preparation  of  small  quantities,  the  re- 
tort is  placed  on  a piece  of  wire-gauze,  and  heated  with  charcoal ; in  this 
process  it  is  always  advisable  to  coat  the  retort  by  repeated  application 
of  a thin  paste  made  of  clay  and  water ; a little  borax  or  carbonate  of 
soda  should  be  added  to  the  water  used  for  making  the  paste. 

Tests. — Red  fuming  nitric  acid  must  be  in  a state  of  the  greatest  possi- 
ble concentration,  and  perfectly  free  from  sulphuric  acid.  In  order  to  de- 
tect minute  traces  of  the  latter,  evaporate  a few  c.  c.  of  the  specimen  in  a 
porcelain  dish  nearly  to  dryness,  dilute  the  residue  with  water,  add  some 
chloride  of  barium,  and  observe  whether  a precipitate  forms  on  standing. 

Uses. — A powerful  oxidizing  agent  and  solvent ; it  serves  more  espe- 
cially to  convert  sulphur  and  metallic  sulphides  into  sulphuric  acid  and 
sulphates  respectively. 

3.  Acetic  Acid  (see  “ Qual.  Anal.”). 

4.  Tartaric  Acid  (see  “ Qual.  Anal.”). 

b.  Hydrogen  Acids  and  Halogens. 

§ 58. 

1.  Hydrochloric  Acid. 

a.  Pure  hydrochloric  acid  of  1T2  sp.  gr.  (see  u Qual.  Anal.”). 

b.  Pure  fuming  hydrochloric  acid  of  about  ITS  sp.  gr. 

Preparation. — As  in  “ Qual.  Anal.”  § 26,  with  this  modification,  how- 
ever, that  only  3 or  4 parts  of  water,  instead  of  6,  are  put  into  the  re- 
ceiver* to  4 parts  of  chloride  of  sodium  in  the  retort.  The  greatest  care 


REAGENTS. 


85 


§58.1 

must  be  taken  to  keep  the  receiver  cool,  and  to  change  it  as  soon  as  the 
tube  through  which  the  gas  is  conducted  into  it  begins  to  get  hot,  since 
it  is  now  no  longer  hydrochloric  acid  gas  which  passes  over,  but  an 
aqueous  solution  of  the  gas,  in  form  of  vapor,  which  would  simply  weaken 
the  fuming  acid,  if  it  were  allowed  to  mix  with  it. 

Tests. — The  fuming  acid  must,  for  many  purposes,  be  perfectly  free 
from  chlorine  and  sulphurous  acid.  For  the  mode  of  testing  for  these 
impurities,  see  “ Qual.  Anal.”  loc.  cit.  Test  for  sulphuric  acid  as  under 
Nitric  Acid,  previous  page. 

Uses. — Fuming  hydrochloric  acid  has  a much  more  energetic  action 
than  the  dilute  acid ; it  is,  therefore,  used  instead  of  the  latter  in  cases 
where  a more  rapid  and  energetic  action  is  desirable. 

2.  Hydrofluoric  Acid. 

This  is  employed  for  the  decomposition  of  silicates  and  borates,  some- 
times in  the  gaseous  form,  sometimes  in  the  condition  of  aqueous  solu- 
tion. In  the  first  case,  the  substance  to  be  decomposed  is  introduced  into 
the  leaden  box,  in  which  the  hydrofluoric  gas  is  being  generated ; in  the 
latter  case,  we  must  first  prepare  the  aqueous  acid.  The  raw  material 
employed  is  fluor  spar  or  kryolite  (Luboldt*).  Both  are  first  finely  pow- 
dered, and  then  treated  with  concentrated  sulphuric  acid.  To  1 part 
kryolite,  2\  parts  sulphuric  acid  are  used ; to  1 part  fluor  spar,  2 parts 
sulphuric  acid  are  used.  If  the  latter  is  employed,  allow  the  mixture  to 
stand  in  a dry  place  for  several  days,  stirring  every  now  and  then,  so 
that  the  silicic  acid  (which  is  generally  contained  in  fluor  spar)  may  first 
escape  in  the  form  of  fluosilicic  gas.  Convenient  distillatory  apparatus 
have  been  described  by  Luboldt  (loc.  cit.)  and  by  H.  Briegleb.|  The 
latter  commends  itself  especially  on  account  of  its  relatively  small  cost.  It 
consists  of  a leaden  retort,  with  a movable  leaden  top,  which  can  be  luted 
on.  The  receiver  belonging  to  it  is  a box  of  lead,  with  a tubulure  at  the 
side,  into  which  the  neck  of  the  retort  just  enters.  The  cover  of  the 
receiver  is  raised  conical,  and  is  provided  at  the  top  with  an  exit  tube 
of  lead.  In  the  receiver  a platinum  dish  containing  water  is  placed,  all 
joints  are  luted,  and  the  retort  is  carefully  heated  in  a sand-bath.  The 
aqueous  hydrofluoric  acid  found  at  the  end  of  the  operation  in  the  plati- 
num dish  is  perfectly  pure.  The  small  quantity  of  impure  hydrofluoric 
acid  which  collects  on  the  bottom  of  the  receiver  is  thrown  away.  The 
hydrofluoric  acid  must  entirely  volatilize  when  heated  in  a platinum  dish 
on  a water-bath.  The  pure  acid  gives  no  precipitate  when  neutralized 
with  potash,  while  silicofluoride  of  potassium  separates  if  the  acid  con- 
tains hydrofluosilicic  acid.  The  acid  is  best  preserved  in  gutta-percha 
bottles,  as  recommended  by  Stadeler.  The  greatest  caution  must  be 
observed  in  preparing  this  acid,  since,  whether  in  the  fluid  or  gaseous 
condition,  it  is  one  of  the  most  injurious  substances. 

3.  Chlorine  and  Chlorine- water  (see  “ Qual.  Anal.”). 

4.  Nitro-hydrochloric  Acid  (see  “ Qual.  Anal.”). 

5.  Hydrofluosilicic  Acid  (see  “ Qual.  Anal.”). 

c.  Sulphur  Acids. 

1.  Hydrosulphuric  Acid  (see  “ Qual.  Anal.”). 


* Joum.  fiir  prakt.  Chem.,  76,  330. 
j*  Anna!,  d.  Chem.  u.  Pharm. , 111,  380. 


86 


REAGENTS. 


III.  BASES  AND  METALS. 
a.  Oxygen  liases  and  Metals . 

§ 59. 

a.  Alkalies . 

1.  Potassa  and  Soda  (see  “ Qual.  Anal.”). 

All  the  three  sorts  of  the  caustic  alkalies  mentioned  in  the  qualitative 
part  are  required  in  quantitative  analysis,  viz.,  common  solution  of  soda, 
hydrate  of  potassa  purified  with  alcohol,  and  solution  of  potassa  prepared 
with  baryta.  Pure  solution  of  potassa  may  be  obtained  also  by  heating 
to  redness  for  half  an  hour  in  a copper  crucible,  a mixture  of  1 part  of 
nitrate  of  potassa,  and  2 or  3 parts  of  thin  sheet  copper  cut  into  small 
pieces,  treating  the  mass  with  water,  allowing  the  oxide  of  copper  to 
subside  in  a tall  vessel,  and  removing  the  supernatant  clear  fluid  by- 
means  of  a syphon  (Wohler).* 

2.  Ammonia  (see  “ Qual.  Anal.”). 

(3.  Alkaline  Earths. 

1.  Baryta  (see  “ Qual.  Anal.”). 

2.  Lime. 

Finely  divided  hydrate  of  lime  mixed  with  water  (milk  of  lime),  is 
used  more  particularly  to  effect  the  separation  of  magnesia,  &c.,  from  the 
alkalies.  Milk  of  lime  intended  to  be  used  for  that  purpose  must,  of 
course,  be  perfectly  free  from  alkalies.  To  insure  this  the  hydrate 
should  be  thoroughly  washed,  by  repeated  boiling  with  fresh  quantities 
of  distilled  water.  This  operation  is  conducted  best  in  a silver  dish. 
When  cold,  the  milk  of  lime  so  prepared  is  kept  in  a well-stoppered 
bottle. 


y.  Heavy  Metals , and  their  Oxides. 


60. 


1.  Zinc. 

Zinc  has  of  late  been  much  used  as  a reagent  in  quantitative  anal  fsis. 
It  serves  more  especially  to  effect  the  reduction  of  dissolved  sesquio^ide 
of  iron  to  protoxide,  and  also  the  precipitation  of  copper  from  the  solu- 
tions of  that  metal.  Zinc  intended  to  be  used  for  the  former  purpose 
must  be  free  from  iron,  for  the  latter  free  from  lead,  copper,  and  other 
metals  wliich  remain  undissolved  upon  treating  the  zinc  with  dilute 
acids. 

To  procure  zinc  which  leaves  no  residue  upon  solution  in  dilute  sub 


* Hydrate  of  soda,  made  by  acting  on  pure  water  by  pure  sodium  and  ft  sing 
in  silver  vessels,  is  to  be  had  cheaply  of  the  Magnesium  Metal  Company,  Sakord, 
Manchester,  England. 


61.] 


REAGENTS. 


87 


phuric  acid,  there  is  commonly  no  other  resource  but  to  re-distil  the  com- 
mercial article. 

This  is  effected  in  a retort  made  of  the  material  of  Hessian  or  black- 
lead  crucibles.  The  operation  is  conducted  in  a wind-furnace  with  good 
draught.  The  neck  of  the  retort  must  hang  down  as  perpendicular  as 
possible.  Under  the  neck  is  placed  a basin  or  small  tub,  filled  with  water. 
The  distillation  begins  as  soon  as  the  retort  is  at  a bright  red  heat.  As 
the  neck  of  the  retort  is  very  liable  to  become  choked  up  with  zinc,  or 
oxide  of  zinc,  it  is  necessary  to  keep  it  constantly  free  by  means  of  a 
pipe-stem.  The  zinc  obtained  by  this  re-distillation  is  nearly  or  quite 
free  from  lead. 

Tests. — The  following  is  the  simplest  way  of  testing  the  purity  of  zinc  : 
dissolve  the  metal  in  dilute  sulphuric  acid  in  a small  flask  provided  with 
a gas-evolution  tube,  place  the  outer  limb  of  the  tube  under  water,  and 
when  the  solution  is  completed,  let  the  water  entirely  or  partly  recede 
into  the  flask  ; after  cooling,  add  to  the  fluid,  drop  by  drop,  a sufficiently 
dilute  solution  of  permanganate  of  potassa.  If  a drop  of  that  solution 
imparts  the  same  red  tint  to  the  zinc  solution  as  to  an  equal  volume  of 
water,  the  zinc  may  be  considered  free  from  iron.  I prefer  this  way  of 
testing  the  purity  of  zinc  to  other  methods,  as  it  affords,  at  the  same  time, 
an  approximate,  or,  if  the  zinc  has  been  weighed,  and  the  chameleon  solu- 
tion (which,  in  that  case,  must  be  considerably  diluted)  measured,  an 
accurate  and  precise  knowledge  of  the  quantity  of  iron  present.  If  lead 
or  copper  are  present,  these  metals  remain  undissolved  upon  solution  of 
the  zinc. 

2.  Oxide  of  Lead. 

Precipitate  pure  nitrate  or  acetate  of  lead  with  carbonate  of  ammonia, 
wash  the  precipitate,  dry,  and  ignite  gently  to  complete  decomposition. 

Oxide  of  lead  is  often  used  to  fix  an  acid,  so  that  it  is  not  expelled 
even  by  a red  heat. 

b.  Sulphur  Bases. 

1.  Sulphide  of  Ammonium  (see  “ Qual.  Anal.”). 

We  require  both  the  colorless  monosulphide,  and  the  yellow  poly* 
sulphide. 

2.  Sulphide  of  Sodium  (see  “ Qual.  Anal.”). 


IV.  SALTS. 
a.  Salts  of  the  Alkalies. 

§ 61. 

1.  Sulphate  of  Potassa  (see  “Qual.  Anal.”). 

2.  Oxalate  of  Ammonia  (see  “ Qual.  Anal.”). 

3.  Acetate  of  Soda  (see  “ Qual.  Anal.”). 

4.  Succinate  of  Ammonia. 


88 


REAGENTS. 


[§  62. 

Preparation. — Saturate  succinic  acid,  which  has  been  purified  by 
dissolving  in  nitric  acid  and  re  crystallizing,  with  dilute  ammonia. 
The  reaction  of  the  new  compound  should  be  rather  slightly  alkaline 
than  acid. 

Uses. — This  reagent  serves  occasionally  to  separate  sesquioxide  of 
iron  from  other  metallic  oxides. 

5.  Carbonate  of  Soda  (see  “ Qual.  Anal.”). 

This  reagent  is  required  both  in  solution  and  in  pure  crystals ; in  the 
latter  form  to  neutralize  an  excess  of  acid  in  a fluid  which  it  is  desir- 
able not  to  dilute  too  much. 

6.  Carbonate  of  Ammonia  (see  Qual.  Anal.”). 

7.  Bisulphite  of  Soda  (see  “ Qual.  Anal.”). 

8.  Hyposulphite  of  Soda. 

This  salt  occurs  in  commerce.  It  should  be  dry,  clear,  well  crystal- 
lized, completely  and  with  ease  soluble  in  water.  The  solution  must 
give  with  nitrate  of  silver  at  first  a white  precipitate,  must  not  effer- 
vesce with  acetic  acid,  and  when  acidified  must  give  no  precipitate  with 
chloride  of  barium,  or  at  most,  only  a slight  turbidity.  The  acidified 
solution  must,  after  a short  time,  become  milky  from  separation  of  sul- 
phur. 

Uses. — The  hyposulphite  of  soda  is  used  for  the  precipitation  of  sev- 
eral metals,  as  sulphides,  particularly  in  separations,  for  instance,  of 
copper  from  zinc ; it  also  serves  as  solvent  for  several  salts  (chloride  of 
silver,  sulphate  of  lime,  &c.)  ; lastly,  it  is  employed  in  volumetric  ana- 
lysis, its  use  here  depending  on  the  reaction  2 (NaO,  S2  02)  + I = Na 
I + Na  O,  S4  05. 

9.  Nitrite  of  Potassa  (see  “ Qual.  Anal.”). 

10.  Bichromate  of  Potassa  (see  “ Qual.  Anal.”). 

11.  Molybdate  of  Ammonia  (see  “ Qual.  Anal.”). 

12.  Chloride  of  Ammonium  (see  “ Qual.  Anal.”). 

13.  Cyanide  of  Potassium  (see  “ Qual.  Anal.”). 

b.  Salts  of  the  Alkaline  Earths. 

§ 62. 

1.  Chloride  of  Barium  (see  “ Qual.  Anal.”). 

The  following  process  gives  a very  pure  chloride  of  barium,  free 
from  lime  and  strontia  : — Transmit  through  a concentrated  solution  of 
impure  chloride  of  barium  hydrochloric  gas,  as  long  as  a precipitate 
continues  to.  form.  Nearly  the  whole  of  the  chloride  of  barium  pre- 
sent is  by  this  means  separated  from  the  solution,  in  form  of  a crystal- 
line powder.  Collect  this  on  a filter,  let  the  adhering  liquid  drain  off, 
wash  the  powder  repeatedly  with  small  quantities  of  pure  hydrochloric 
acid,  until  a sample  of  the  washings,  diluted  with  water,  and  precipitated 
with  sulphuric  acid,  gives  a filtrate  which,  upon  evaporation  in  a plati- 
num dish,  leaves  no  residue.  The  hydrochloric  mother-liquor  serves  to 
dissolve  fresh  portions  of  witherite.  I make  use  of  the  chloride  of 
barium  so  obtained,  principally  for  the  preparation  of  perfectly  pure 
carbonate  of  baryta,  which  is  often  required  in  quantitative  analyses. 

2.  Acetate  of  Baryta. 


REAGENTS. 


89 


§63.] 

Preparation. — Dissolve  pure  carbonate  of  baryta  in  moderately  di- 
lute acetic  acid,  filter,  and  evaporate  to  crystallization. 

Tests. — Dilute  solution  of  acetate  of  baryta  must  not  be  rendered 
turbid  by  solution  of  nitrate  of  silver.  See  also  “ Qual.  Anal.,”  Chlo- 
ride of  barium , the  same  tests  being  also  used  to  ascertain  the  purity 
of  the  acetate. 

Uses. — Acetate  of  baryta  is  used  instead  of  chloride  of  barium,  to 
effect  the  precipitation  of  sulphuric  acid,  in  cases  where  it  is  desirable 
to  avoid  the  introduction  of  a chloride  into  the  solution,  or  to  convert 
the  base  into  an  acetate.  As  the  reagent  is  seldom  required,  it  is  best 
kept  in  crystals. 

3.  Carbonate  of  Baryta  (see  “ Qual.  Anal.”). 

4.  Chloride  of  Strontium. 

Preparation. — Chloride  of  strontium  is  prepared  from  strontianite 
or  celestine,  by  the  same  processes  as  chloride  of  barium.  The  pure 
crystals  obtained  are  dissolved  in  spirit  of  wine  of  96  per  cent.,  the 
solution  is  filtered,  and  kept  for  use. 

Uses. — The  alcoholic  solution  of  chloride  of  strontium  is  used  to  ef- 
fect the  conversion  of  alkaline  sulphates  into  chlorides,  in  cases  where 
it  is  desirable  to  avoid  the  introduction  into  the  fluid  of  a salt  insoluble 
in  spirit  of  wine. 

5.  Chloride  of  Calcium  (see  “ Qual.  Anal.”). 

6.  Sulphate  of  Magnesia  (see  “ Qual.  Anal.”). 

This  reagent  is  principally  used  to  precipitate  phosphoric  acid  from 
aqueous  solutions.  The  solution  required  for  this  purpose  should  be 
kept  ready  prepared  ; it  is  made  by  dissolving  1 part  of  crystallized 
sulphate  of  magnesia  and  1 part  of  pure  chloride  of  ammonium  in  8 
parts  of  water  and  4 parts  of  solution  of  ammonia,  allowing  the  fluid 
to  stand  at  rest  for  several  days,  and  then  filtering. 

This  solution  is  sometimes  called  magnesia-mixture. 

c.  Salts  of  the  Oxides  of  the  Heavy  Metals . 

§ 63- 

1.  Sulphate  of  Protoxide  of  Iron  (see  “ Qual.  Anal.”). 

2.  Sesquichloride  of  Iron  (see  “ Qual.  Anal.”). 

3.  Acetate  of  Sesquioxide  of  Uranium. 

Heat  finely  powdered  pitchblende  with  dilute  nitric  acid,  filter  the 
fluid  from  the  undissolved  portion,  and  treat  the  filtrate  with  hydro- 
sulphuric  acid  to  remove  the  lead,  copper,  and  arsenic ; filter  again, 
evaporate  to  dryness,  extract  the  residue  with  water,  and  filter  the  so- 
lution from  the  oxides  of  iron,  cobalt,  and  manganese.  Nitrate  of  ses- 
quioxide of  uranium  crystallizes  from  the  filtrate  ; purify  this  by  recrys- 
tallization, and  then  heat  the  crystals  until  a small  portion  of  the  ses- 
quioxide of  uranium  is  reduced.  Warm  the  yellowish-red  mass  thus 
obtained  with  acetic  acid,  filter  and  let  the  filtrate  crystallize.  The 
crystals  are  acetate  of  sesquioxide  of  uranium,  and  the  mother-liquor 
contains  the  undecomposed  nitrate  (Wertheim). 

Tests. — Solution  of  acetate  of  sesquioxide  of  uranium  after  acidifica- 
tion with  hydrochloric  acid  must  not  be  altered  by  hydrosulphuric  acid  ; 


REAGENTS. 


90 


[§  64. 


carbonate  of  ammonia  must  produce  in  it  a precipitate,  soluble  in  an 
excess  of  the  precipitant. 

Uses. — Acetate  of  sesquioxide  of  uranium  may  serve,  in  many  cases, 
to  effect  the  separation  and  determination  of  phosphoric  acid. 

4.  Nitrate  of  Silver  (see  “ Qual.  Anal.”). 

5.  Acetate  of  Lead  (see  “ Qual.  Anal.”). 

6.  Chloride  of  Mercury  (see  “ Qual.  Anal.”). 

7.  Protochloride  of  Tin  (see  “ Qual.  Anal.”). 

8.  Bichloride  of  Platinum  (see  “ Qual.  Anal.”). 

9.  Sodio-Protochloride  of  Palladium  (see  “ Qual.  Anal.”). 

P.  BEAGENTS  FOB  GBAVIMETBIC  ANALYSIS  IN 
THE  DBY  WAY. 

§ 64. 

1.  Carbonate  of  Soda,  pure  anhydrous  (see  “ Qual.  Anal.”). 

2.  Mixed  Carbonates  of  Soda  and  Potassa  (see  “ Qual.  Anal.”). 

3.  Hydrate  of  Baryta  (see  “ Qual.  Anal.”  and  § 59). 

4.  Nitrate  of  Potassa  (see  “ Qual.  Anal.”). 

5.  Nitrate  of  Soda  (see  “ Qual.  Anal.”). 

6.  Borax  (fused). 

Preparation. — Heat  crystallized  borax  (see  “ Qual.  Anal.”)  in  a 
platinum  or  porcelain  dish,  until  there  is  no  further  intumescence  ; re- 
duce the  porous  mass  to  powder,  and  heat  this  in  a platinum  crucible 
until  it  is  fused  to  a transparent  mass.  Pour  the  semi-fluid,  viscid  mass 
upon  a fragment  of  porcelain.  A better  way  is  to  fuse  the  borax 
in  a net  of  platinum  gauze,  by  making  the  gas  blowpipe-flame  act  upon 
it.  The  drops  are  collected  in  a platinum  dish.  The  vitrified  borax  ob- 
tained is  kept  in  a well-stoppered  bottle.  But  as  it  is  always  necessary 
to  heat  the  vitrified  borax  previous  to  use,  to  make  quite  sure  that  it  is 
perfectly  anhydrous,  the  best  way  is  to  prepare  it  only  when  required. 

Uses. — Vitrified  borax  is  used  to  effect  the  expulsion  of  carbonic  acid 
and  other  volatile  acids,  at  a red  heat. 

7.  Bisulphate  of  Potassa. 

Preparation. — Mix  87  parts  of  neutral  sulphate  of  potassa  (see  “ Qual. 
Anal.”),  in  a platinum  crucible,  with  49  parts  of  concentrated  pure  sul- 
phuric acid,  and  heat  to  gentle  redness  until  the  mass  is  in  a state  of 
uniform  and  limpid  fusion.  Pour  the  fused  salt  on  a fragment  of  porce- 
lain, or  into  a platinum  dish  standing  in  cold  water.  After  cooling, 
break  the  mass  into  pieces,  and  keep  for  use.* 

Uses. — This  reagent  serves  as  a flux  for  certain  native  compounds  of 
alumina  and  sesquioxide  of  chromium.  Bisulphate  of  potassa  is  used 
also,  as  we  have  already  had  occasion  to  state,  for  the  cleansing  of  plati- 
num crucibles  ; for  this  latter  purpose,  however,  the  salt  which  is  ob- 
tained in  the  preparation  of  nitric  acid  will  be  found  sufficiently  pure. 

8.  Carbonate  of  Ammonia  (solid). 

Preparation. — See  “ Qual.  Anal.” — This  reagent  serves  to  convert  the 

* [J.  Lawrence  Smith  advises  the  use  of  bisulphate  of  soda  for  fluxing  alumi- 
nous compounds,  as  the  fused  mass  is  much  more  readily  soluble  in  water.  ] 


REAGENTS. 


91 


§65.] 

bisulphates  of  the  alkalies  into  neutral  salts.  It  must  completely  vola- 
tilize when  heated  in  a platinum  dish. 

9.  Nitrate  of  Ammonia. 

Preparation. — Neutralize  pure  carbonate  of  ammonia  with  pure  nitric 
acid,  warm,  and  add  ammonia  to  slightly  alkaline  reaction ; filter,  if  ne- 
cessary, and  let  the  filtrate  crystallize.  Fuse  the  crystals  in  a platinum 
dish,  and  pour  the  fused  mass  upon  a piece  of  porcelain ; break  into 
pieces  whilst  still  warm,  and  keep  in  a well-stoppered  bottle. 

Tests. — Nitrate  of  ammonia  must  leave  no  residue  when  heated  in  a 
platinum  dish. 

Uses. — Nitrate  of  ammonia  serves  as  an  oxidizing  agent ; for  instance, 
to  convert  lead  into  oxide  of  lead,  or  to  effect  the  combustion  of  carbon, 
in  cases  where  it  is  desired  to  avoid  the  use  of  fixed  salts. 

10.  Chloride  of  Ammonium. 

Preparation  and  Tests. — See  “ Qual.  Anal.” 

Uses. — Chloride  of  ammonium  is  often  used  to  convert  metallic  oxides 
and  acids,  e.g .,  oxide  of  lead,  oxide  of  zinc,  binoxide  of  tin,  arsenic  acid, 
antimonic  acid,  &c.,  into  chlorides  (ammonia  and  water  escape  in  the 
process).  Many  metallic  chlorides  being  volatile,  and  others  volatilizing 
in  presence  of  chloride  of  ammonium  fumes,  they  may  be  completely  re- 
moved by  igniting  them  with  chloride  of  ammonium  in  excess,  and  thus 
many  compounds,  e.g.,  alkaline  antimoniates,  may  be  easily  and  expedi- 
tiously analyzed.  Chloride  of  ammonium  is  also  used  to  convert  various 
salts  with  other  acids  into  chlorides,  e.g.,  small  quantities  of  alkaline 
sulphates. 

11.  Hydrogen  Gas. 

Preparation. — Hydrogen  gas  is  evolved  when  dilute  sulphuric  acid  is 
added  to  granulated  zinc.  It  may  be  purified  from  traces  of  foreign 
gases  either  by  passing  first  through  chloride  of  mercury  solution,  then 
through  potash  solution,  or  as  recommended  by  Stenhouse,  by  passing 
through  a tube  filled  with  pieces  of  charcoal.  If  the  gas  is  desired  dry, 
pass  through  sulphuric  acid  or  a chloride  of  calcium  tube. 

Tests. — Pure  hydrogen  gas  is  inodorous.  It  ought  to  burn  with  a 
colorless  flame,  which,  when  cooled  by  depressing  a porcelain  dish  upon 
it,  must  deposit  nothing  on  the  surface  of  the  dish  except  pure  water 
(free  from  acid  reaction). 

Uses. — Hydrogen  gas  is  frequently  used,  in  quantitative  analysis,  to 
reduce  oxides,  chlorides,  sulphides,  &c.,  to  the  metallic  state. 

12.  Chlorine. 

Preparation. — See  “ Qual  Anal.” — Chlorine  gas  is  purified  and  dried 
by  transmitting  it  through  concentrated  sulphuric  acid,  or  a chloride  of 
calcium  tube. 

Uses. — Chlorine  gas  serves  principally  to  produce  chlorides,  and  to 
separate  the  volatile  from  the  non-volatile  chlorides ; it  is  also  used  to 
displace  and  indirectly  determine  bromine  and  iodine. 

C.  REAGENTS  USED  IN  VOLUMETRIC  ANALYSIS. 

§ 65. 

Under  this  head  are  arranged  the  most  important  of  those  substances, 


92 


REAGENTS, 


[§  65. 


which  serve  for  the  preparation  and  testing  of  the  fluids  required  in 
volumetric  analysis,  and  have  not  been  given  sub  A and  B. 

1.  Pure  Crystallized  Oxalic  Acid. 

The  introduction  of  crystallized  oxalic  acid  as  a basis  for  alkalimetry 
and  acidimetry  is  due  to  Fr.  Mohr.  It  is  also  employed  to  determine 
the  strength  of,  or  to  standardize , a solution  of  permanganate  of  potassa, 

1 equivalent  of  permanganic  acid  being  required  to  convert  5 equivalents 
of  oxalic  acid*  into  carbonic  acid  (Mn2  07  + 2 S 03  + 5 C2  03  =*  2 (Mn 
O,  S 03 ) + 10  C 02  ).  We  use  in  most  cases  the  pure  crystallized  acid 
which  has  the  formula  C2  03,  HO  -(-  2 aq.,  and  of  which  the  equivalent 
is  accordingly  63. 

Preparation. — Treat  powdered  oxalic  acid  of  commerce,  in  a flask,  with 
lukewarm  distilled  water,  in  such  proportion  as  will  leave  a large 
amount  of  the  acid  undissolved,  and  shake  (Mohr).  Filter,  crystallize, 
and  let  the  crystals  drain  ; then  spread  them  out  on  blotting-paper,  and 
let  them  get  thoroughly  dry,  at  the  common  temperature,  in  a place  free 
from  dust ; or  press  them  gently  between  sheets  of  blotting-paper,  and 
repeat  the  operation  with  fresh  sheets,  until  the  crystals  are  quite  dry. 
Another  method,  by  which  the  acid  is  obtained  perfectly  pure,  consists 
in  decomposing  oxalate  of  lead  with  dilute  sulphuric  acid. 

Tests. — The  crystals  of  oxalic  acid  must  not  show  the  least  sign  of 
efflorescence  (to  which  they  are  liable  even  at  20°  in  a dry  atmosphere) ; 
they  must  dissolve  in  water  to  a perfectly  clear  fluid  ; when  heated  in  a 
platinum  dish,  they  must  leave  no  fixed  and  incombustible  residue  (car- 
bonate of  lime,  carbonate  of  potassa,  &c.).  If  the  acid  obtained  by  a 
first  crystallization  fails  to  satisfy  these  requirements,  it  must  be  recrys- 
tallized. 

2.  Tincture  of  Litmus. 

Preparation. — Digest  1 part  of  litmus  of  commerce  with  6 parts  of 
water,  on  the  water-bath,  for  some  time,  filter,  divide  the  blue  fluid  into 

2 portions,  and  saturate  in  one  half  the  free  alkali,  by  stirring  repeat- 
edly with  a glass  rod  dipped  in  very  dilute  nitric  acid,  until  the  color 
just  appears  red  ; add  the  remaining  blue  half,  together  with  1 part  of 
strong  spirit  of  wine,  and  keep  the  tincture,  which  is  now  ready  for  use, 
in  a small  open  bottle,  not  quite  full,  in  a place  protected  from  dust. 
In  a stoppered  bottle  the  tincture  would  speedily  loose  color. 

Tests. — Litmus  tincture  is  tested  by  coloring  with  it  about  100  cubic 
centimetres  of  water  distinctly  blue,  dividing  the  fluid  into  two  por- 
tions, and  adding  to  the  one  the  least  quantity  of  a dilute  acid,  to  the 
other  a trace  of  solution  of  soda.  If  the  one  portion  acquires  a dis- 
tinct red,  the  other  a distinct  blue  tint,  the  litmus  tincture  is  fit  for 
use,  as  neither  acid  nor  alkali  predominates. 

3.  Permanganate  of  Potassa. 

Preparation. — Mix  8 parts  of  very  finely  powdered  pure  pyrolusite, 
or  binoxide  of  manganese,  with  7 parts  of  chlorate  of  potassa,  put  the 
mixture  into  a shallow  cast-iron  pot,  and  add  37  parts  of  a solution 
of  potassa  of  1*27  specific  gravity  (the  same  solution  as  is  used  in 
organic  analysis  f)  ; evaporate  to  dryness,  stirring  the  mixture  during 


* Considered  as  a monobasic  acid. 

f Or  instead  of  the  solution,  use  10  parts  of  the  hydrate  (K  O,  H O).  In  this 


REAGENTS. 


93 


§ 65.1 

the  operation  ; put  the  residue  before  it  has  absorbed  moisture,  into 
an  iron  or  Hessian  crucible,  and  expose  to  a dull-red  heat,  with  fre- 
quent stirring  with  an  iron  rod  or  iron  spatula,  until  no  more  aqueous 
vapors  escape  and  the  mass  is  in  a faint  glow.  Remove  the  crucible  now 
from  the  lire,  and  transfer  the  friable  mass  to  an  iron  pot.  Reduce  to 
coarse  powder,  and  transfer  this,  in  small  portions  at  a time,  to  an  iron 
vessel  containing  100  parts  of  boiling  water;  keep  boiling,  replacing  the 
evaporating  water,  and  passing  a stream  of  carbonic  acid  through  the 
fluid.  (Mulder* *).  The  originally  dark  green  solution  of  manganate  of 
potassa  soon  changes,  with  separation  of  hydrated  binoxide  of  manganese, 
to  the  deep  violet-red  of  the  permanganate.  When  it  is  considered  that 
the  conversion  is  complete',  allow  to  settle,  take  out  a small  quantity  of 
the  clear  liquid,  boil  and  pass  carbonic  acid  through  it.  If  a precipitate 
forms,  the  conversion  is  not  yet  complete. 

The  solution  may  be  filtered  through  gun-cotton.  Evaporate,  crystal- 
lize, and  dry  the  crystals  on  a porous  tile. 

The  pure  salt  is  now  to  be  obtained  in  commerce. 

4.  Ammonio-Sulphate  of  Protoxide  of  Iron. 

(Fe  O,  S 03+N  H4  O,  S 0,+  6 aq.) 

Fr.  Mohr  has  proposed  to  employ  this  double  salt,  which  is  not  liable 
to  efflorescence  and  oxidation,  as  an  agent  to  determine  the  strength  of 
the  permanganate  solution. 

Preparation. — Take  two  equal  portions  of  dilute  sulphuric  acid,  and 
warm  the  one  with  a moderate  excess  of  small  iron  nails  free  from  rust, 
until  the  evolution  of  hydrogen  gas  has  altogether  or  very  nearly  ceased  ; 
neutralize  the  other  portion  exactly  with  carbonate  of  ammonia,  and 
then  add  to  it  a few  drops  of  dilute  sulphuric  acid.  Filter  the  solution 
of  the  sulphate  of  the  protoxide  of  iron  into  that  of  the  sulphate  of  am- 
monia, evaporate  the  mixture  a little,  if  necessary,  and  then  allow  the 
salt  to  crystallize.  Let  the  crystals,  which  are  hard  and  of  a pale  green 
color,  drain  in  a funnel,  then  wash  them  in  a little  water,  dry  thoroughly 
on  blotting-paper  in  the  air,  and  keep  for  use. 

The  equivalent  of  the  salt  (196)  is  exactly  7 times  that  of  iron  (28). 
The  solution  of  the  salt  in  water  which  has  been  just  acidified  with  sul- 
phuric acid  must  not  become  red  on  the  addition  of  sulphocyanide  of 
potassium. 

[5.  Ammonia-Iron- Alum. 

(Fe2  03,  3 S03  + NH4  O,  S03,  + 24  HO.) 

Preparation. — Bring  into  a large  porcelain  dish  58  grms.  of  pure 
crystallized  ferrous  sulphate  (see  Fresenius’  “ Qual.  Anal.”  Am.  ed.  p.  73), 
together  with  a quantity  of  oil  of  vitriol  equivalent  to  8 '3  grms.  of  an- 
hydrous sulphuric  acid  (see  Table,  p.  488).  Heat  upon  a sand-bath,  add- 
ing nitric  acid  from  time  to  time,  in  small  portions,  until  the  iron  has 
all  passed  into  ferric  oxide,  or  until  a drop  of  the  solution  gives  no  blue 
coloration  with  ferricyanide  of  potassium.  Heat  further,  and  evap- 
orate until  the  excess  of  nitric  acid  is  expelled,  then  add  14  grms. 


case  fuse  the  potash  and  the  chlorate  together  first,  and  then  project  the  manga’ 
nese  into  the  crucible. 

* Jahresbericht  von  Kopp  und  Will,  1858,  581. 


94 


REAGENTS. 


[§65. 


of  sulphate  of  ammonia,*  and,  if  need  he,  hot  water  sufficient  to  bring 
the  salt  into  solution ; filter  into  a porcelain  capsule  and  set  aside,  under 
cover,  to  crystallize. 

The  iron-alum  separates  in  cubo-octahedrons,  which  may  be  yellowish, 
lilac,  or  colorless.  If  dark  in  color,  dissolve  in  warm  water,  add  a few 
drops  of  oil  of  vitriol,  and  crystallize  again.  Rinse  the  pale  or  colorless 
crystals,  after  separation  from  the  mother-liquor,  with  cold  water,  wrap 
up  closely  in  filter  paper,  and  allow  them  to  dry  at  the  ordinary  tem- 
perature, f 

The  yield  should  be  about  80  grms.  The  dry  salt  should  be  pulver- 
ized, pressed  between  folds  of  paper  until  freed  from  mechanically  ad- 
hering water,  and  preserved  in  a well-stoppered  bottle. 

Uses . — Ammonia-iron-alum  furnishes  the  best  means  of  obtaining  a 
definite  quantity  of  ferric  oxide  for  making  standard  solutions,  being 
easily  obtained  pure  and  inalterable  if  kept  away  from  acid  vapors.  Its 
purity  may  be  readily  controlled  by  ascertaining  the  loss  on  careful  igni- 
tion, which  should  leave  a residue  of  16*6  per  cent,  of  sesquioxide  of 
iron,  corresponding  to  11*59  per  cent,  of  metallic  iron. 

6.  Pure  Iodine. 

Preparation. — Triturate  iodine  of  commerce  with  -J-  part  of  its  weight 
of  iodide  of  potassium,  dry  the  mass  in  a large  watch-glass  with  ground 
rim,  warm  this  gently  on  a sand-bath,  or  on  an  iron  plate,  and  as  soon  as 
violet  fumes  begin  to  escape,  cover  it  with  another  watch-glass  of  the 
same  size.  Continue  the  application  of  heat  until  all  the  iodine  is  sub- 
limed, and  keep  in  a well-closed  glass  bottle.  The  chlorine  or  bromine, 
which  is  often  found  in  iodine  of  commerce,  combines,  in  this  process, 
with  the  potassium,  and  remains  in  the  lower  watch-glass,  together  with 
the  excess  of  iodide  of  potassium. 

Tests. — Iodine  purified  by  the  process  just  now  described,  must  leave 
no  fixed  residue  when  heated  on  a watch-glass.  But,  even  supposing  it 
should  leave  a trace  on  the  glass,  it  would  be  of  no  great  consequence, 
as  the  small  portion  intended  for  use  has  to  be  resublimed  immediately 
before  weighing. 


* If  not  on  hand,  this  salt  may  be  prepared  by  saturating  oil  of  vitriol  with 
carbonate  of  ammonia  and  evaporating  to  dryness.  30  grammes  of  oil  of  vitriol 
give  somewhat  more  than  is  required  above. 

f Examinations  of  iron-alum  thus  prepared  show  that  the  variations  in  the 
color  of  the  salt,  from  colorless  to  rose,  are  not  connected  with  appreciable  differ- 
ences of  composition. 

J.  H.  Grove,  of  the  Sheffield  Laboratory,  obtained  the  following  results  in  the 
examination  of  ammonia-iron-alum  crystals,  the  ferric  oxide  being  estimated  by 
ignition : — 


Fe2  O3 

j 

[ 16  59 

1st 

16-55 

1 

16-59 

2d 

16-53 

3d 

16-57 

4th 

16-57 

5th 

16-58 

6th  •! 

| 16-50 

1 16-56 

7th 

16-55 

Calculated  16  '60 

REAGENTS. 


95 


§65.1 

Uses .-  -Pure  iodine  is  used  to  determine  the  amount  of  iodine  con- 
tained in  the  solution  of  iodine  in  iodide  of  potassium,  employed  in 
many  volumetric  processes. 

7.  Iodide  of  Potassium. 

Small  quantities  of  this  article  may  be  procured  cheaper  in  commerce 
than  prepared  in  the  laboratory.  For  the  preparation  of  iodide  of  potas- 
sium intended  for  analytical  purposes  I recommend  Baup’s  method,  im- 
proved by  Frederking,  because  the  product  obtained  by  this  process  is 
free  from  iodic  acid. 

Tests. — Put  a sample  of  the  salt  in  dilute  sulphuric  acid.  If  the  iodide 
is  pure,  it  will  dissolve  without  coloring  the  fluid  ; but  if  it  contain 
iodate  of  potassa,  the  fluid  will  acquire  a brown  tint,  from  the  presence 
of  free  iodine  (K  I + H O + S 03=K  O,  S 03  + H land  I 0|  + 5 H 1= 
5 H O + 6 I,  which  remain  in  solution  in  the  hydriodic  acid).  Mix  the 
solntion  of  another  sample  with  nitrate  of  silver,  as  long  as  a precipitate 
continues  to  form ; add  solution  of  ammonia  in  excess,  shake  the  mix- 
ture, filter,  and  supersaturate  the  filtrate  with  nitric  acid.  The  forma- 
tion of  a white,  curdy  precipitate  indicates  the  presence  of  chloride  in 
the  iodide  of  potassium.  Presence  of  sulphate  of  potassa  is  detected  by 
means  of  solution  of  chloride  of  barium,  with  addition  of  some  hydro- 
chloric acid. 

U ses. — Iodide  of  potassium  is  used  as  a solvent  for  iodine  in  the  pre- 
paration of  standard  solutions  of  iodine ; it  is  employed  also  to  absorb 
free  chlorine.  In  the  latter  case  every  equivalent  of  chlorine  liberates 
an  equivalent  of  iodine,  which  is  retained  in  solution  by  the  agency  of  the 
excess  of  iodide  of  potassium.  The  iodide  of  potassium  intended  for  these 
uses  must  be  free  from  iodate  and  carbonate  of  potassa ; the  presence  of 
trifling  traces  of  chloride  of  potassium  or  sulphate  of  potassa  is  of  no 
consequence. 

8.  Arsenious  Acid. 

The  arsenious  acid  sold  in  the  shops  in  large  pieces,  externally  opaque, 
but  often  still  vitreous  within,  is  generally  quite  pure.  The  purity  of  the 
article  is  tested  by  moderately  heating  it  in  a glass  tube,  open  at  both  ends, 
through  which  a feeble  current  of  air  is  transmitted.  Pure  arsenious 
acid  must  completely  volatilize  in  this  process ; no  residue  must  be  left  in 
the  tube  upon  the  expulsion  of  the  sublimate  from  it.  If  a non-volatile 
residue  is  left  which,  when  heated  in  a current  of  hydrogen  gas,  turns 
black,  the  arsenious  acid  contains  teroxide  of  antimony,  and  is  unfit  for 
use  in  analytical  processes.  Dissolve  about  10  grms.  of  the  arsenious  acid 
to  be  tested  in  soda,  and  add  1 — 2 drops  acetate  of  lead.  If  a brownish 
color  is  produced,  the  arsenious  acid  contains  sulphide  of  arsenic  and 
cannot  be  used.  Arsenious  acid  is  employed,  in  form  of  arsenite  of  soda, 
to  determine  hypochlorous  acid,  free  chlorine,  iodine,  &c. 

9.  Chloride  of  Sodium. 

Perfectly  pure  rock-salt  is  best  suited  for  analytical  purposes.  It  must 
dissolve  in  water  to  a clear  fluid ; oxalate  of  ammonia,  phosphate  of  soda, 
and  chloride  of  barium  must  not  trouble  the  solution.  Pure  chloride  of 
sodium  may  be  prepared  also  by  Margueritte’s  process,  viz.,  conduct  into 
a concentrated  solution  of  common  salt  hydrochloric  gas  to  saturation, 
collect  the  small  crystals  of  chloride  of  sodium  which  separate  on  a fun- 


96 


REAGENTS. 


B 66’ 

nel,  let  them  thoroughly  drain,  wash  with  hydrochloric  acid,  and  dry  the 
chloride  of  sodium  finally  in  a porcelain  dish,  until  the  hydrochloric  acid 
adhering  to  it  has  completely  evaporated.  The  mother-liquor,  which 
contains  the  small  quantities  of  sulphate  of  lime,  chloride  of  magnesium, 
&c.,  originally  present  in  the  salt,  is  at  the  next  preparation  of  hydro- 
chloric acid  added  to  the  ingredients  in  the  retort,  instead  of  a corre- 
sponding portion  of  water. 

Uses. — Chloride  of  sodium  serves  as  a volumetric  precipitating  agent 
in  the  determination  of  silver,  and  also  to  determine  the  strength  of  solu- 
tions of  silver  intended  for  the  estimation  of  chlorine.  We  usually  fuse 
it  before  weighing.  The  operation  must  be  conducted  with  caution,  and 
must  not  be  continued  longer  than  necessary  ; for  if  the  gas-flame  acts 
on  the  salt,  hydrochloric  acid  escapes,  while  carbonate  of  soda  is  formed. 

10.  Metallic  Silver. 

The  silver  obtained  by  the  proper  reduction  of  the  pure  chloride  of 
the  metal  alone  can  be  called  chemically  pure.  The  silver  precipitated 
by  copper  is  never  absolutely  pure,  but  contains  generally  about  y-oVo" 
of  copper. 

Chemically  pure  silver  is  only  used  in  small  quantity  to  prepare  the 
dilute  solution  employed  for  the  determination  of  silver.  The  solution 
of  silver  required  for  the  estimation  of  chlorine  need  not  be  made  with 
absolutely  pure  silver,  as  the  strength  of  this  solution  had  always  best 
be  determined  after  the  preparation,  by  means  of  pure  chloride  of  sodium. 


D.  REAGENTS  USED  IN  ORGANIC  ANALYSIS. 

§ 66. 

1.  Oxide  of  Copper. 

Preparation. — Stir  pure*  copper  scales  (which  should  first  be  ignited 
in  a muffle)  with  pure  nitric  acid  in  a porcelain  dish  to  a thick  paste  ; 
after  the  effervescence  has  ceased,  heat  gently  on  the  sand-bath  un- 
til the  mass  is  perfectly  dry.  Transfer  the  green  basic  salt  produced  to 
a Hessian  crucible,  and  heat  to  a moderate  redness,  until  no  more  fumes 
of  hyponitric  acid  escape ; this  may  be  known  by  the  smell,  or  by  intro- 
ducing a small  portion  of  the  mass  into  a test  tube,  closing  the  latter 
with  the  finger,  heating  to  redness,  and  then  looking  through  the  tube 
lengthways.  The  uniform  decomposition  of  the  salt  in  the  crucible  may 
be  promoted  by  stirring  the  mass  from  time  to  time  with  a hot  glass  rod. 
When  the  crucible  has  cooled  a little,  reduce  the  mass,  which  now  con- 
sists of  pure  oxide  of  copper,  to  a tolerably  fine  powder,  by  triturating 
it  in  a brass  or  porcelain  mortar ; pass  through  a metal  sieve,  and  keep 
in  a well-stoppered  bottle  for  use.  It  is  always  advisable  to  leave  a 
small  portion  of  the  oxide  in  the  crucible,  and  to  expose  this  again  to  an 
intense  red  heat.  This  agglutinated  portion  is  not  pounded,  but  simply 
broken  into  small  fragments. 


* If  the  scales  contain  lime,  digest  them  with  water,  containing  a little  nitrio 
acid,  for  a long  time,  wash,  and  then  proceed  as  above. 


REAGENTS. 


97 


gGG.] 

Tests. — Pure  oxide  of  copper  is  a compact,  heavy,  deep-black  pow- 
der, gritty  to  the  touch ; upon  exposure  to  a red  heat  it  must  evolve  no 
hyponitric  acid  fumes,  nor  carbonic  acid;  the  latter  would  indicate 
presence  of  fragments  of  charcoal,  or  particles  of  dust.  It  must  contain 
nothing  soluble  in  water.  That  portion  of  the  oxide  which  has  been  ex- 
posed to  an  intense  red  heat  should  be  hard,  and  of  a grayish-black  color. 

Uses. — Oxide  of  copper  serves  to  oxidize  the  carbon  and  hydrogen  of 
organic  substances,  yielding  up  its  oxygen  wholly  or  in  part,  according 
to  circumstances.  That  portion  of  the  oxide  which  has  been  heated  to 
the  most  intense  redness  is  particularly  useful  in  the  analysis  of  volatile 
fluids. 

N.B.  The  oxide  of  copper,  after  use,  may  be  regenerated  by  oxidation 
with  nitric  acid,  and  subsequent  ignition.  Should  it  have  become  mixed 
with  alkaline  salts  in  the  course  of  the  analytical  process,  it  is  first  digested 
with  very  dilute  cold  nitric  acid,  and  washed  afterwards  with  water.  To 
purify  oxide  of  copper  containing  chloride,  E.  Erlenmeyer  recommends 
to  ignite  it  in  a tube,  first  in  a stream  of  moist  air,  and  finally,  when  the 
escaping  gas  ceases  to  redden  litmus  paper,  in  dry  air.  By  these  opera- 
tions any  oxides  of  nitrogen  that  may  have  remained  are  also  removed. 

2.  Chromate  of  Lead. 

Preparation. — Precipitate  a clear  filtered  solution  of  acetate  of  lead, 
slightly  acidulated  with  acetic  acid,  with  a small  excess  of  bichromate  of 
potassa  ; wash  the  precipitate  by  decantation,  and  at  last  thoroughly  on 
a linen  strainer ; dry,  put  in  a Hessian  crucible,  and  heat  to  bright 
redness  until  the  mass  is  fairly  in  fusion.  Pour  out  upon  a stone  slab  or 
iron  plate,  break,  pulverize,  pass  through  a fine  metallic  sieve,  and  keep 
the  tolerably  fine  powder  for  use. 

Tests. — Chromate  of  lead  is  a heavy  powder,  of  a dirty  yellowish-brown 
color.  It  must  evolve  no  carbonic  acid  upon  the  application  of  a red  heat ; 
the  evolution  of  carbonic  acid  would  indicate  contamination  with  organic 
matter,  dust,  &c.  It  must  contain  nothing  soluble  in  water. 

Uses. — Chromate  of  lead  serves,  the  same  as  oxide  of  copper,  for  the 
combustion  of  organic  substances.  It  is  converted,  in  the  process  of  com- 
bustion, into  sesquioxide  of  chromium  and  basic  chromate  of  lead.  It 
suffers  the  same  decomposition,  with  evolution  of  oxygen,  when  heated 
by  itself  above  its  point  of  fusion.  The  property  of  chromate  of  lead  to 
fuse  at  a red  heat  renders  it  preferable  to  oxide  of  copper  as  an  oxidizing 
agent,  in  cases  where  we  have  to  act  upon  difficultly  combustible  sub- 
stances. 

N.B.  Chromate  of  lead  may  be  used  a second  time.  For  this  purpose 
it  is  fused  again  (being  first  roasted,  if  necessary),  and  then  powdered. 
After  having  been  twice  used  it  is  powdered,  moistened  with  nitric  acid, 
dried,  and  fused.  In  this  way  the  chromate  of  lead  may  be  used  over  and 
over  again  indefinitely  (Yohl*). 

3.  Oxygen  Gas. 

Preparation. — Triturate  100  grammes  of  chlorate  of  potassa  with 
exactly  0*1  grm.  of  finely-powdered  sesquioxide  of  iron,  and  introduce 
the  mixture  into  a plain  retort,  which  must  not  be  more  than  half  full ; 
expose  the  retort,  over  a charcoal  fire,  at  first  to  a gentle,  and  then  to  a 


* Annalen  d.  Chem.  u.  Pharm.,  106,  127. 


98 


REAGENTS. 


[§  66. 


gradually  increased  heat.  As  soon  as  the  salt  begins  to  fuse,  shake  the 
retort  a little,  that  the  contents  may  be  uniformly  heated.  The  evolution 
of  oxygen  speedily  commences,  and  proceeds  rapidly,  but  not  impetuously, 
provided  the  above  proportion  between  the  chlorate  of  potassa  and  the 
sesquioxide  of  iron  be  adhered  to.  As  soon  as  the  air  is  expelled  from 
the  retort,  connect  the  glass  tube,  fixed  in  the  neck  of  the  retort  by  means 
of  a tight-fitting  perforated  cork,  with  an  india-rubber  tube  inserted  into 
the  lower  orifice  of  the  gasometer ; the  glass  tube  must  be  sufficiently 
wide,  and  there  must  be  sufficient  space  left  around  the  india-rubber  to 
permit  the  free  efflux  of  the  displaced  water.  Continue  the  application 
of  heat  to  the  retort  until,  incipient  redness  having  been  reached,  the 
evolution  of  gas  has  altogether  or  very  nearly  ceased.  It  is  advisable 
to  coat  the  retort  up  to  the  middle  of  the  body  with  several  layers  of  a 
thin  paste  made  of  clay  and  water,  with  addition  of  a little  carbonate  of 
soda  or  borax. 

100  grammes  of  chlorate  of  potassa  give  about  27  litres  of  oxygen  gas. 

The  oxygen  gas  produced  by  this  process  is  moist,  and  may  contain 
traces  of  carbonic  acid  gas,  and  also  of  chlorine.  The  gas  prepared  from 
a mixture  of  chlorate  of  potassa  with  a comparatively  large  proportion  of 
binoxide  of  manganese  always  contains  a rather  considerable  quantity  of 
chlorine  gas.  These  impurities  must  be  removed,  and  the  oxygen  gas 
thoroughly  dried,  before  it  can  be  used  in  elementary  organic  analysis. 
The  gas  is  therefore  passed  from  the  gasometer,  first  through  a Liebig’s 
bulb-apparatus  filled  with  solution  of  potassa  of  1 *27  sp.  gr.,  then  through 
a U-tube  containing  pumice-stone,  moistened  with  sulphuric  acid,  after- 
wards through  several  tubes  filled  with  hydrate  of  potassa,  and  lastly 
through  a chloride  of  calcium  tube. 

Tests. — A chip  of  wood  which  has  been  kindled  and  blown  out,  so  as 
to  leave  a spark  at  the  extremity,  must  immediately  burst  into  flame  in  a 
current  of  oxygen  gas.  The  gas  must  not  trouble  lime-water,  nor  solution 
of  nitrate  of  silver  when  transmitted  through  these  fluids. 

4.  Soda-lime. 

Preparation. — Take  ordinary  solution  of  soda,  ascertain  its  specific 
gravity,  weigh  out  a certain  quantity,  calculate  by  means  of  the  table, 
§ 206,  the  weight  of  the  hydrate  of  soda  that  must  be  present,  add  twice 
this  latter  weight  of  the  best  quick-lime,  and  then  evaporate  to  dryness 
in  an  iron  vessel.  Heat  the  residue  in  an  iron  or  Hessian  crucible,  keep 
for  some  time  at  a low  red  heat,  and  reduce  the  mass,  whilst  still  warm, 
to  a tolerably  fine  powder,  by  pounding  and  sifting  through  a metallic 
sieve.  Keep  the  powder  in  a well-stoppered  bottle. 

Tests. — Soda-lime  must  not  effervesce  too  much  when  treated  with 
dilute  hydrochloric  acid  in  excess ; but,  more  particularly,  it  must  not 
evolve  ammonia  when  mixed  with  pure  sugar,  and  heated  to  redness. 
It  must  not  swell  and  fuse  so  readily  as  to  obstruct  the  bore  of  a tube 
when  heated  to  low  redness,  nor  must  it  remain  infusible  and  but 
loosely  coherent  after  exposure  to  a bright  red-heat.  The  former  diffi- 
culty may  be  remedied  by  mixture  with  dry  slaked  lime,  the  latter  by 
mixing  with  a portion  of  insufficiently  ignited  soda-lime  kept  in  reserve 
for  this  purpose. 

Uses. — Soda-lime  serves  for  the  analysis  of  nitrogenous  organic  sub- 
stances. For  the  rationale  of  its  action,  see  the  chapter  on  Organic 
Analysis. 


§66.] 


REAGENTS. 


99 


5.  Metallic  Copper. 

Metallic  copper  serves,  in  the  analysis  of  nitrogenous  substances,  to 
effect  the  reduction  of  the  nitric  oxide  gas  that  may  form  in  the  course 
of  the  analytical  process. 

It  is  used  either  in  the  form  of  turnings,  or  in  that  of  close  wire  spirals ; 
or  of  small  rolls  made  of  thin  sheet  copper.  A length  of  from  7 to  10 
centimetres  is  given  to  the  spirals  or  rolls,  and  just  sufficient  thickness 
to  admit  of  their  being  inserted  into  the  combustion  tube.  To  have  it 
perfectly  free  from  dust,  oxide,  &c.,  it  is  first  heated  to  redness  in  the 
open  air,  in  a crucible,  until  the  surface  is  oxidized  ; it  is  then  put  into 
a glass  or  porcelain  tube,  through  which  an  uninterrupted  current  of 
dry  hydrogen  gas  is  transmitted ; and  when  all  atmospheric  air  has  been 
expelled  from  the  evolution  apparatus  and  the  tube,  the  latter  is  in  its 
whole  length  heated  to  redness.  The  operator  should  make  sure  that 
the  atmospheric  air  has  been  thoroughly  expelled,  before  he  proceeds 
to  apply  heat  to  the  tube ; neglect  of  this  precaution  may  lead  to  an 
explosion. 

6.  Potassa. 

a.  Solution  of  Potassa. 

Solution  of  potassa  is  prepared  from  the  carbonate,  with  the  aid  of 
milk  of  lime,  in  the  way  described  in  the  “ Qualitative  Analysis,”  for 
the  preparation  of  solution  of  soda.  The  proportions  are — 1 part  of 
carbonate  of  potassa  to  12  parts  of  water,  and  § part  of  lime,  slaked  to 
paste  with  three  times  the  quantity  of  warm  water. 

The  decanted  clear  solution  is  evaporated,  in  an  iron  vessel,  over  a 
strong  fire,  until  it  has  a specific  gravity  of  1*27  ; it  is  then,  whilst  still 
warm,  poured  into  a bottle,  which  is  well  closed,  and  allowed  to  stand 
at  rest  until  all  solid  particles  have  subsided.  The  clear  solution  is 
finally  drawn  off  from  the  deposit,  and  kept  for  use. 

b . Hydrate  of  Potassa  (common). 

The  commercial  hydrate  of  potassa  in  sticks  will  answer  the  purpose. 
If  you  wish  to  prepare  it,  evaporate  solution  of  potassa  (a)  in  a silver 
vessel,  over  a strong  fire,  until  the  residuary  hydrate  flows  like  oil,  and 
white  fumes  begin  to  rise  from  the  surface.  Pour  the  fused  mass  out 
on  a clean  iron  plate,  and  break  it  up  into  small  pieces.  Keep  in  a 
well-stoppered  bottle  for  use. 

c.  Hydrate  of  Potassa  (purified  with  alcohol),  see  “ Qual.  Anal.” 
p.  43. 

Uses . — Solution  of  potassa  serves  for  the  absorption,  and  at  the  same 
time  for  the  estimation  of  carbonic  acid.  In  many  cases,  a tube  filled 
with  hydrate  of  potassa  is  used,  in  addition  to  the  apparatus  filled  with 
solution  of  potassa.  Hydrate  of  potassa  purified  with  alcohol,  which 
is  perfectly  free  from  sulphate  of  potassa,  is  employed  for  the  determi- 
nation of  sulphur  in  organic  substances. 

7.  Chloride  of  Calcium. 

a.  Crude  fused  Chloride  of  Calcium . 

Preparation . — Digest,  with  warm  water,  the  residuary  mixture  of 


100 


REAGENTS. 


[§  66. 

chloride  of  calcium  and  lime  which  remains  after  the  preparation  of 
ammonia ; filter,  neutralize  the  alkaline  filtrate  exactly  with  hydrochlo- 
ric acid,  and  evaporate  to  dryness  in  an  iron  pan ; fuse  the  residue  in 
an  iron  or  Hessian  crucible,  pour  out  the  fused  mass,  and  break  into 
pieces.  Preserve  it  in  well-stoppered  bottles. 

b.  Pure  Chloride  of  Calcium. 

Preparation. — Dissolve  the  crude  chloride  of  calcium  of  a in  lime- 
water,  filter  the  solution,  and  neutralize  exactly  with  hydrochloric  acid  ; 
evaporate,  in  a porcelain  dish,  to  dryness,  and  expose  the  residue  for 
several  hours  to  a tolerably  strong  heat  (about  200°),  on  the  sand-bath. 
The  white  and  porous  mass  obtained  by  this  process  consists  of  Ca  Cl 
-j-  2 aq. 

Uses. — The  crude  fused  chloride  of  calcium  serves  to  dry  moist 
gases ; the  pure  chloride  is  used  in  elementary  organic  analysis  for  the 
absorption  and  estimation  of  the  water  formed  by  the  hydrogen  con- 
tained in  the  analyzed  substance.  The  solution  of  the  pure  chloride  of 
calcium  must  not  show  an  alkaline  reaction. 

8.  Bichromate  of  Potassa. 

Bichromate  of  potassa  of  commerce  is  purified  by  repeated  recrystal- 
lization, until  chloride  of  barium  produces,  in  the  solution  of  a sample 
of  it  in  water,  a precipitate  which  completely  dissolves  in  hydrochloric 
acid.  Bichromate  of  potassa  thus  perfectly  free  from  sulphuric  acid  is 
required  more  particularly  for  the  oxidation  of  organic  substances  with 
a view  to  the  estimation  of  the  sulphur  contained  in  them.  Where  the 
salt  is  intended  for  other  purposes,  e.g .,  to  determine  the  carbon  of  or- 
ganic bodies,  by  heating  them  with  chromate  of  potassa  and  sulphuric 
acid,  one  recrystallization  is  sufficient. 


SECTION  III. 


FORMS  AND  COMBINATIONS  IN  WHICH  SUBSTANCES 
ARE  SEPARATED  FROM  EACH  OTHER,  OR  IN  WHICH 
THEIR  WEIGHT  IS  DETERMINED. 

§ 67. 

The  quantitative  analysis  of  a compound  substance  requires,  as  the  first 
and  most  indispensable  condition,  a correct  and  accurate  knowledge  of 
the  composition  and  properties  of  the  new  combinations  into  which  it  is 
intended  to  convert  its  several  individual  constituents,  for  the  purpose 
of  separating  them  from  one  another,  and  determining  their  several 
weights.  Regarding  the  properties  of  the  new  compounds,  we  have  to 
inquire  more  particularly,  in  the  first  place,  how  they  behave  with  sol- 
vents ; secondly,  what  is  their  deportment  in  the  air;  and,  thirdly, what 
is  their  behavior  on  ignition  ? It  may  be  laid  down  as  a general  rule, 
that  compounds  are  the  better  adapted  for  quantitative  determination 
the  more  insoluble  they  are,  and  the  less  alteration  they  undergo  upon 
exposure  to  air  or  to  a high  temperature. 

The  composition  of  bodies  is  expressed  either  in  per-cents,  or  in  stoi- 
chiometrical  or  symbolic  formulae ; by  means  of  the  latter,  the  consti- 
tution of  the  more  frequently  recurring  compounds  may  be  easily  re- 
membered. In  this  Section  the  composition  of  the  substances  treated 
of  is  given  in  three  different  ways,  in  as  many  columns  : the  first  column 
gives  the  composition  of  the  substance  in  symbols  ; the  second,  in  equi- 
valents (H  = 1)  ; the  third,  in  per-cents.  With  respect  to  its  composi- 
tion, a compound  is  the  better  adapted  for  the  quantitative  determina- 
tion of  a body  the  less  it  contains  relatively  of  that  body  ; since  any  error 
or  loss  of  substance  that  may  occur  in  the  course  of  the  analytical  pro- 
cess will  exercise  the  less  influence  upon  the  accuracy  of  the  results. 
Thus,  ammonio-bichloride  of  platinum,  for  instance,  is,  in  this  respect, 
better  adapted  than  chloride  of  ammonium  for  the  determination  of 
nitrogen;  since  the  former  contains  only  6*27  per  cent.,  while  the  latter 
contains  26.2  per  cent,  of  the  element  in  question. 

Suppose  we  have  to  analyze  a nitrogenous  substance  ; — we  estimate  its 
nitrogen  in  the  form  of  bichloride  of  platinum  and  chloride  of  ammonium. 
When  the  process  is  conducted  with  absolute  accuracy,  0*300  grm.  of 
the  analyzed  body  yields  T000  grm.  of  ammonio-bichloride  of  platinum: 
100  parts  of  this  double  chloride  contain  6*27  parts  of  nitrogen,  T000 
contains  therefore  0*0627  of  that  element.  These  0*0627  have  been  de- 
rived from  0*300  of  substance;  100  parts  of  the  analyzed  body,  conse- 
quently, contain  20*90  of  nitrogen. 

We  now  make  a second  analysis,  in  which  we  convert  the  nitrogen  of 
the  substance  to  be  analyzed  into  chloride  of  ammonium,  instead  of 
bichloride  of  platinum  and  chloride  of  ammonium : we  again  con- 
duct the  process  with  absolute  accuracy,  and  obtain  from  0*300  of  the 


FORMS. 


102 


[§  68. 


substance  under  examination,  0*2394  of  chloride  of  ammonium,  corre- 
sponding to  0*0627  of  nitrogen,  or  20*90  per  cent. 

Now,  let  us  assume  a loss  of  10  milligrammes  to  have  occurred  in 
each  process: — this  will  alter  the  result,  in  the  first  instance,  from  1*000 
to  0*990  of  bichloride  of  platinum  and  chloride  of  ammonium,  corre- 
sponding to  0*062073  of  nitrogen,  or  20*69  per  cent.;  the  loss  of  nitrogen 
will  therefore  be  20*90— 20*69=0*21. 

In  the  second  instance  the  result  will  be  altered  from  0*2394  to  0*2294 
of  chloride  of  ammonium,  corresponding  to  0*0601  of  nitrogen,  or  20.03 
per  cent.  The  loss  in  this  case  will  consequently  amount  to  0*87. 

We  see  here  that  the  same  error  occasions,  in  the  one  case,  a loss  of 
0*21  per  cent.,  with  respect  to  the  amount  of  nitrogen;  whilst,  in  the 
other  case,  the  loss  amounts  to  0*87  per  cent. 

We  will  now  proceed  to  enumerate  and  examine  those  combinations 
of  the  several  bodies  which  are  best  adapted  for  their  quantitative 
determination.  The  description  given  of  the  external  form  and  appear- 
ance of  the  new  compounds  relates  more  particularly  to  the  state  in 
which  they  are  obtained  in  our  analyses.  With  regard  to  the  proper- 
ties of  the  new  compounds,  we  shall  confine  ourselves  to  the  enumeration 
of  those  which  bear  upon  the  special  object  we  have  more  immediately 
in  view. 

A. — Forms  in  which  the  bases  are  weighed  or  precipitated. 


BASES  OF  THE  FIRST  GROUP. 

§ 68. 

1.  Potassa  (or  Potash). 

The  combinations  best  suited  for  the  weighing  of  potassa  are,  sul- 
phate OF  POTASSA,  CHLORIDE  OF  POTASSIUM,  BICHLORIDE  OF  PLATINUM 
and  chloride  of  potassium  (Potassio-Bichloride  of  Platinum). 

a.  Sulphate  of  potassa , in  the  analytical  process,  is  obtained  as  a 
white  crystalline  mass.  It  dissolves  with  some  difficulty  in  water  (1 
part  requiring  10  parts  of  water  of  12°),  it  is  almost  absolutely  insoluble 
in  pure  alcohol,  but  slightly  more  soluble  in  alcohol  containing  sulphuric 
acid  (Expt.  No.  6).  It  does  not  affect  vegetable  colors ; it  is  unalter- 
able in  the  air.  The  crystals  decrepitate  strongly  when  heated.  When 
very  strongly  ignited  for  a long  time  the  salt  loses  weight  a little,  even 
when  reducing  gases  are  excluded, — the  residue  possesses  an  alkaline  re- 
action. When  exposed  to  a red  heat,  in  conjunction  with  chloride  of 
ammonium,  sulphate  of  potassa  is  partly,  and,  upon  repeated  application 
of  the  process,  wholly,  converted,  with  effervescence,  into  chloride  of 
potassium  (H.  Pose). 

composition. 


KO 47*11  54*08 

S 03  40*00  45*92 


87*11  100*00 

Bisulphate  of  potassa  (K  O,  S 03+H  O,  S 03),  which  is  always  pro- 
duced when  the  neutral  salt  is  evaporated  to  dryness  with  free  sulphuric 
acid,  is  readily  soluble  in  water,  and  fusible  even  at  a moderate  heat.  At 
a red  heat  it  loses  half  its  sulphuric  acid,  together  with  the  basic  water, 
but  not  readily — the  complete  conversion  of  the  acid  into  the  neutral 


BASES  OF  GROUP  I. 


103 


§ 69.] 

salt  requiring  the  long-continued  application  of  an  intense  red  heat. 
However,  when  heated  in  an  atmosphere  of  carbonate  of  ammonia — 
which  may  be  readily  procured  by  repeatedly  throwing  into  the  faint 
red-hot  crucible  containing  the  bisulphate,  small  lumps  of  pure  carbonate 
of  ammonia,  and  putting  on  the  lid — the  acid  salt  changes  readily  and 
quickly  to  the  neutral  sulphate.  The  transformation  may  be  considered 
complete  as  soon  as  the  salt,  which  was  so  readily  fusible  before,  assumes 
the  solid  state,  at  a faint  red  heat. 

b.  Chloride  of  potassium  is  obtained  in  analysis  as  cubic  crystals,  or  as 
a crystalline  mass.  It  is  readily  soluble  in  water,  but  much  less  so  in 
dilute  hydrochloric  acid  ; in  absolute  alcohol  it  is  nearly  insoluble,  and 
but  slightly  soluble  in  spirit  of  wine.  It  does  not  affect  vegetable  colors, 
and  is  unalterable  in  the  air.  When  heated  it  decrepitates,  unless  it  has 
been  kept  long  drying,  with  expulsion  of  a little  water  mechanically  con- 
fined in  it.  At  a moderate  red  heat  it  fuses  unaltered,  and  without 
diminution  of  weight ; when  exposed  to  a higher  temperature,  it  volatilizes 
in  white  fumes ; this  volatilization  proceeds  the  more  slowly,  the  more 
effectually  the  access  of  air  is  prevented  (Expt.  No.  7).  When  repeat- 
edly evaporated  with  solution  of  oxalic  acid  in  excess,  it  is  converted  in- 
to oxalate  of  potassa.  When  evaporated  with  excess  of  nitric  acid,  it  is 
converted  readily  and  completely  into  nitrate.  On  ignition  with  oxalate 
of  ammonia,  carbonate  of  potassa  and  cyanide  of  potassium  are  formed  in 
noticeable  quantities. 


K 39-11  52-45 

Cl 35-46  47-55 


74-57  100-00 

c.  ^Bichloride  of  platinum  and  chloride  of  potassium  (Potassio-bichlo- 
ride  of  Platinum)  presents  either  small  reddish-yellow  octahedra,  or  a 
lemon-colored  powder.  It  is  difficultly  soluble  in  cold,  more  readily  in 
hot  water ; nearly  insoluble  in  absolute  alcohol,  and  but  sparingly  sol- 
uble in  spirit  of  wine — one  part  requiring  for  its  solution,  respectively, 
12083  parts  of  absolute  alcohol,  3775  parts  of  spirit  of  wine  of  76  per  cent, 
and  1053  parts  of  spirit  of  wine  of  55  per  cent.  (Expt.  No.  8,  a). 
Presence  of  free  hydrochloric  acid  sensibly  increases  the  solubility 
(Expt.  No.  8,  b).  In  caustic  potassa  it  dissolves  completely  to  a yellow 
fluid.  It  is  unalterable  in  the  air,  and  at  100°.  On  exposure  to  an  in- 
tense red  heat,  2 eq.  of  chlorine  escape,  metallic  platinum  and  chloride 
of  potassium  being  left;  but  even  after  long-continued  fusion,  there 
remains  always  a little  potassio-bichloride  of  platinum  which  resists 
decomposition.  Complete  decomposition  is  easily  effected,  by  igniting 
the  double  salt  in  a current  of  hydrogen  gas,  or  with  some  oxalic  acid. 


K .... 
Pt . . . . 
Cl3. . . . 

. ..  39-11 

. . . 98-94 

. ..  106-38 

16-00 

40-48 

43-52 

K Cl  .... 
Pt  Cl2. . . . 

74-57 
. . 169-86 

30-51 

69-49 

244-43 

100-00 

244-43 

100-00 

§ 69. 

2.  Soda. 

Soda  is  usually  weighed  as  sulphate  of  soda,  chloride  of  sodium, 


FORMS. 


104 


r§  69. 


or  carbonate  of  soda.  It  is  separated  from  potassa  in  the  form  of 

SODIO-BICHLORIDE  OF  PLATINUM. 

a.  The  anhydrous  neutral  sulphate  of  soda  is  a white  powder  or  p 
white  very  friable  mass.  It  dissol  ves  readily  in  water ; but  is  sparingly 
soluble  in  absolute  alcohol;  presence  of  free  sulphuric  acid  slightly  in- 
creases its  solubility  in  that  menstruum ; it  is  somewhat  more  readily 
soluble  in  spirit  of  wine  (Expt.  No.  9).  It  does  not  affect  vegetable 
colors;  upon  exposure  to  moist  air,  it  slowly  absorbs  water  (Expt.  No. 
10).  When  heated  to  fusion,  it  scarcely  loses  weight,  but  when  exposed 
to  a white  heat  for  a long  time,  it  decidedly  loses  weight,  even  when 
reducing  gases  are  excluded ; the  residue  then  shows  a slight  alkaline 
reaction.  When  ignited  with  chloride  of  ammonium,  it  comports  itself 
the  same  as  sulphate  of  potassa  under  similar  circumstances. 


Na  0 31  43-66 

S 03 40  56-34 


71  100-00 

Bisulphate  of  soda  (Na  O,  S 03  -f-  H O,  S 03),  which  is  always  pro- 
duced upon  the  evaporation  of  a solution  of  the  neutral  salt  with  sul- 
phuric acid  in  excess,  fuses  even  at  a gentle  heat ; it  may  be  readily 
converted  into  the  neutral  salt,  in  the  same  manner  as  the  bisulphate 
of  potassa  is  converted  into  the  neutral  sulphate  (see  § 68,  a). 

b.  Chloride  of  sodium  crystallizes  in  cubes.  In  analysis  it  is  fre- 
quently obtained  as  an  amorphous  mass.  It  dissolves  readily  in  water, 
but  is  much  less  soluble  in  hydrochloric  acid  ; it  is  nearly  insoluble  in  ab- 
solute alcohol,  and  but  sparingly  soluble  in  spirit  of  wine.  100  parts 
of  spirit  of  wine  of  75  per  cent,  dissolve  at  a temperature  of  15°,  0*7 
part.  It  is  neutral  to  vegetable  colors.  Exposed  to  a somewhat  moist 
atmosphere,  it  slowly  absorbs  water  (Expt.  No.  12).  Crystals  of  this 
salt  that  have  not  been  kept  drying  a considerable  time  decrepitate 
when  heated.  The  salt  fuses  at  a red  heat  without  decomposition  ; at 
a white  heat,  and  in  open  vessels  even  at  a bright  red  heat,  it  volati- 
lizes in  white  fumes  (Expt.  No.  13).  If  a carburetted  hydrogen  flame 
acts  on  fusing  chloride  of  sodium,  hydrochloric  acid  escapes,  and  some 
carbonate  of  soda  is  formed.  On  evaporation  with  oxalic  or  nitric  acids, 
as  well  as  by  ignition  with  oxalate  of  ammonia,  it  comports  itself  like 
the  corresponding  salt  of  potassa. 


Na 23-00  39-34 

Cl 35-46  60-66 


58-46  100-00 

c.  Anhydrous  carbonate  of  soda  is  a white  powder  or  a white  very 
friable  mass.  It  dissolves  readily  in  water,  but  much  less  so  in  solu- 
tion of  ammonia  (Margueritte)  ; it  is  insoluble  in  alcohol.  Its  re- 
action is  strongly  alkaline.  Exposed  to  the  air,  it  absorbs  water  slow- 
ly. On  moderate  ignition  to  incipient  fusion  it  scarcely  loses  weight ; 
on  long  fusion,  however,  it  volatilizes  to  a considerable  extent  (Comp, 


Expt.  14). 

NaO 31  58-49 

C 02 22  41-51 


53 


100-00 


§70.] 


BASES  OF  GROUP  I. 


105 


d.  Sodio-bicldoride  of  platinum  crystallizes  with  6 equivalents  of 
water  (Na  Cl,  Pt  Cl2  4*  6 aq.),  in  light  yellow,  transparent,  prismatic 
crystals  which  dissolve  readily  both  in  water  and  in  spirit  of  wine. 

§ 70. 

3.  Ammonia. 

Ammonia  is  most  appropriately  weighed  as  chloride  of  ammonium, 
or  as  bichloride  of  platinum  and  chloride  of  ammonium  (aminonio- 
bichloride  of  platinum). 

Under  certain  circumstances,  ammonia  may  also  be  estimated  from 
the  volume  of  the  nitrogen  gas  eliminated  from  it. 

a.  Chloride  of  ammonium  is  obtained  in  analysis  as  a white  mass. 
It  dissolves  readily  in  water,  but  difficultly  in  spirit  of  wine.  It  does 
not  alter  vegetable  colors,  and  remains  unaltered  in  the  air.  Solution 
of  chloride  of  ammonium,  when  evaporated  on  the  water-bath,  loses  a 
small  quantity  of  ammonia,  and  becomes  slightly  acid.  The  “diminu- 
tion of  weight  occasioned  by  this  loss  of  ammonia  is  very  trifling 
(Expt.  No.  15).  At  100°  chloride  of  ammonium  loses  nothing,  or  very 
little  of  its  weight  (comp,  same  Expt).  At  a higher  temperature  it  vo- 
latilizes readily,  and  without  undergoing  decomposition. 

% 

NH4 18-00  33-67  NHS 17*00  31*80 

Cl 35-46  66-33  H Cl 36-46  68-20 


53-46  100-00  53-46  100-00 

b.  Bichloride  of  platinum  and  chloride  of  ammonium  (ammonio- 
bichloride  of  platinum)  occurs  either  as  a heavy  lemon-colored  powder, 
or  in  small,  hard  octahedral  crystals  of  a bright  yellow  color.  It  is  dif- 
ficultly soluble  in  cold,  but  more  readily  in  hot  water.  It  is  very  spar- 
ingly soluble  in  absolute  alcohol,  but  more  readily  in  spirit  of  wine — 
1 part  requiring  of  absolute  alcohol,  26535  parts  ; of  spirit  of  wine  of 
76  per  cent.,  1406  parts  ; of  spirit  of  wine  of  55  per  cent.,  665  parts. 
The  presence  of  free  acid  sensibly  increases  its  solubility  (Expt.  No. 
16).  It  remains  unaltered  in  the  air,  and  at  100°.  Upon  ignition  chlo- 
rine and  chloride  of  ammonium  escape,  leaving  the  metallic  platinum  as  a 
porous  mass  (spongy  platinum).  However,  if  due  care  be  not  taken  in 
this  process  to  apply  the  heat  gradually,  the  escaping  fumes  will  carry 
off  particles  of  platinum,  which  will  coat  the  lid  of  the  crucible. 


N H4  . . . 

18-00 

8-06 

nh3  .. 

17-00 

7-61 

Pt 

98-94 

44*30 

H Cl  .. 

36-46 

16-33 

Cl3 

106-38 

47-64 

Pt  Cla . 

169-86 

76-06 

223-32 

100-00 

223-32 

100-00 

NH4  Cl. 

53-46 

23-94 

N 

14-00 

6-27 

Pt  Cl3  . . 

169-86 

76-06 

H4 . . . . 

4-00 

1-79 

Pt  . . . . 

98-94 

44-30 

Cl3. . . . 

106-38 

47-64 

223-32 

100-00 

223-32 

100-00 

106 


FORMS. 


[§  71. 

c.  Nitrogen  gas  is  colorless,  tasteless,  and  inodorous  ; it  mixes  with 
air  without  producing  the  slightest  coloration  ; it  does  not  affect  vege- 
table colors.  Its  specific  gravity  is  0*96978  (air  = 1).  One  litre  (one 
cubic  decimeter)  weighs  at  0°,  and  0*76  meter  of  the  barometer, 
1*25456  grm.  It  is  difficultly  soluble  in  water,  1 volume  of  water  ab- 
sorbing, at  0°,  and  0*76  pressure,  0*02035  vol. ; at  10°,  0*01607  vol.  ; 
at  15°,  0*01478  vol.  of  nitrogen  gas  (Bunsen). 

BASES  OF  THE  SECOND  GROUP. 

§ 71. 

1.  Baryta. 

Baryta  is  weighed  as  sulphate  of  baryta,  carbonate  of  baryta,  and 

SILICO-FLUORIDE  OF  BARIUM. 

a.  Artificially  prepared  sulphate  of  baryta  presents  the  appearance  of 
a fine  white  powder.  When  recently  precipitated,  it  is  difficult  to  ob- 
tain a clear  filtrate,  especially  if  the  precipitation  was  effected  without 
the  aid  of  heat,  and  the  solution  contains  neither  hydrochloric  acid  nor 
chloride  of  ammonium.  It  is  insoluble  in  cold  and  in  hot  water.  It 
has  a great  tendency,  upon  precipitation,  to  carry  down  with  it  other 
substances  contained  in  the  solution  from  which  it  separates,  more  par- 
ticularly nitrate  of  baryta,  chloride  of  barium,  sesquioxide  of  iron,  &c. 
These  substances  can  generally  be  completely  removed  only  after  igni- 
tion, by  washing  with  appropriate  solvents.  Even  the  precipitate  ob- 
tained from  a solution  of  chloride  of  barium  by  means  of  sulphuric  acid 
in  excess  contains  traces  of  chloride  of  barium,  which  it  is  impossible  to 
remove,  even  by  washing  with  boiling  water,  but  which  are  dissolved 
by  nitric  acid  (Siegle).  Cold  dilute  acids  dissolve  trifling,  yet  appre- 
ciable traces  of  sulphate  of  baryta  ; for  instance,  1000  parts  of  nitric 
acid  of  1*032  sp.  gr.  dissolve  0*062  parts  of  Ba  O,  S 03.  Cold  concentra- 
ted acids  dissolve  considerably  more  ; thus,  1000  parts  of  nitric  acid  of 
1*167  sp.  gr.  dissolve  2 parts  of  Ba  O,  S 03  (Calvert).  Boiling  hydro- 
chloric acid  also  dissolves  appreciable  traces  ; thus  230  c.  c.  of  hydro- 
chloric acid  of  TO 2 sp.  gr.  were  found,  after  a quarter  of  an  hour’s  boil- 
ing with  0*679  grm.  of  sulphate  of  baryta,  to  have  dissolved  of  it  0*048 
grm.  Acetic  acid  dissolves  less  sulphate  of  baryta  than  the  other  acids ; 
thus,  80  c.  c.  of  acetic  acid  of  1*02  sp.  gr.  were  found,  after  a quarter  of 
an  hour’s  boiling  with  0*4  grm.  of  Ba  O,  S 03,  to  have  dissolved  only  0*002 
grm.  (Siegle).  Free  chlorine  considerably  increases  the  solubility  of 
sulphate  of  baryta  (O.  L.  Erdmann).  Several  salts  more  particularly 
interfere  with  the  precipitation  of  baryta  by  sulphuric  acid.  I observed 
this  some  time  ago  with  chloride  of  magnesium,  but  nitrate  of  ammonia 
(Mittentzwey)  and  alkaline  citrates  (Spiller)  possess  this  property  in 
a high  degree.  In  the  last  case  the  precipitate  appears  on  the  addition 
of  hydrochloric  acid.  If  a fluid  contains  metaphosphoric  acid,  baryta 
cannot  be  completely  precipitated  out  of  it  by  means  of  sulphuric  acid  ; 
the  resulting  precipitate  too  is  not  pure,  but  contains  phosphoric  acid 
(Scheerer,  Bube).  Sulphate  of  baryta  remains  quite  unaltered  in  the 
air  at  100°,  and  even  at  a red  heat.  On  ignition  with  charcoal,  or  un- 
der the  influence  of  reducing  gases,  it  is  converted  comparatively  easily, 
but  as  a rule  only  partially,  into  sulphide  of  barium.  On  ignition  with 
chloride  of  ammonium,  sulphate  of  baryta  undergoes  partial  decompo- 


§72.] 


BASES  OF  GROUP  II. 


107 


sition.  It  is  not  affected,  or  affected  but  very  slightly,  by  cold  solu- 
tions of  alkaline  bicarbonates  or  of  carbonate  of  ammonia  ; solutions  of 
the  monocarbonates  of  the  fixed  alkalies  when  cold  have  only  a slight 
decomposing  action  upon  it  ; but  when  boiling,  and  upon  repeated  ap- 
plication, they  effect  at  last  the  complete  decomposition  of  the  salt  (H. 
Rose).  By  fusion  with  alkaline  carbonates,  sulphate  of  baryta  is  readily 
decomposed . 


Ba  O 76*5  65*67 

S03  40*0  34*33 


116-5  100-00 

b.  Artificially  prepared  carbonate  of  baryta  is  a white  powder.  It 
dissolves  in  14137  parts  of  cold,  and  in  15421  parts  of  boiling  water 
(Expt.  No.  17).  It  dissolves  far  more  readily  in  solutions  of  chloride 
of  ammonium  or  nitrate  of  ammonia ; from  these  solutions  it  is,  how- 
ever, precipitated  again,  though  not  completely,  by  caustic  ammonia. 
In  water  containing  free  carbonic  acid,  carbonate  of  baryta  dissolves  to 
bicarbonate.  In  water  containing  ammonia  and  carbonate  of  ammonia,  it 
is  nearly  insoluble,  one  part  requiring  about  141000  parts  (Expt.  No. 18). 

Its  solution  in  water  has  a very  faint  alkaline  reaction.  Alkaline 
citrates  and  metaphosphates  impede  the  precipitation  of  baryta  by  car- 
bonate of  ammonia.  It  is  unalterable  in  the  air,  and  at  a red  heat. 
When  exposed  to  the  strongest  heat  of  a blast-furnace,  it  slowly  yields 
up  the  whole  of  its  carbonic  acid ; this  expulsion  of  the  carbonic  acid  is 
promoted  by  the  simultaneous  action  of  aqueous  vapor.  Upon  heating 
it  to  redness  with  charcoal,  caustic  baryta  is  formed,  with  evolution  of 
carbonic  oxide  gas. 

BaO 76-5  77-67 

C 02  22-0  22-33 


98-5  100-00 


c.  Silico-fluoride  of  barium  forms  small,  hard,  and  colorless  crystals, 
or  (more  generally)  a crystalline  powder.  It  dissolves  in  3800  parts 
of  cold  water;  in  hot  water  it  is  more  readily  soluble  (Expt.  No.  19). 
The  presence  of  free  hydrochloric  acid  increases  its  solubility  considera- 
bly (Expt.  No.  20).  Chloride  of  ammonium  acts  also  in  the  same  way 
(1  part  silico-fluoride  of  barium  dissolves  in  428  parts  of  saturated,  and 
589  parts  of  dilute  solution  of  chloride  of  ammonium.  J.  W.  Mallet). 
In  spirit  of  wine  it  is  almost  insoluble.  It  is  unalterable  in  the  air,  and 
at  100°  ; when  ignited,  it  is  decomposed  into  fluoride  of  silicon,  which 
escapes,  and  fluoride  of  barium,  which  remains. 


Ba  FI 
Si  Fl2 


. . 87-5 

62-72 

Ba. . . . 

. . 68-5 

49-10 

..  52-0 

37-28 

Si  ... , 

. ..  14-0 

10-04 

. . . 

. . 57-0 

40-86 

139-5 

100-00 

139-5 

100-00 

§72. 

2.  Strontia. 

Strontia  is  weighed  either  as  sulphate  of  strontia,  or  as  carbonate 

OF  STRONTIA. 


108 


FORMS. 


[§  73 

a.  Sulphate  of  strontia,  artificially  prepared,  is  a white  powder.  It 
dissolves  in  6895  parts  of  cold,  and  9638  parts  of  boiling  water  (Expt.  No. 
21).  In  water  containing  sulphuric  acid,  it  is  still  more  difficultly  solu- 
ble, requiring  from  11000  to  12000  parts  (Expt.  No.  22).  Of  cold 
hydrochloric  acid  of  8*5  per  cent.,  it  requires  474  parts ; of  cold  nitric 
acid  of  4*8  per  cent.,  432  parts  ; of  cold  acetic  acid  of  15*6  per  cent,  of 
A,  IIO,  as  much  as  7843  parts  (Expt.  No.  23).  It  dissolves  in  solution 
of  chloride  of  sodium,  but  is  precipitated  again  from  this  solution  by 
sulphuric  acid.  Metaphosphoric  acid  (Scheerer,  Rube),  and  also  alka- 
line citrates,  but  not  free  citric  acid  (Spiller),  impede  the  precipitation 
of  strontia  by  sulphuric  acid.  It  is  nearly  insoluble  both  in  absolute 
alcohol  and  in  spirit  of  wine.  It  does  not  alter  vegetable  colors  ; and 
remains  unaltered  in  the  air,  and  at  a red  heat.  When  exposed  to  a 
most  intense  red  heat,  it  fuses  without  undergoing  decomposition. 
When  ignited  with  charcoal,  or  under  the  influence  of  reducing  gases,  it 
is  converted  into  sulphide  of  strontium.  The  solutions  of  carbonates 
and  bicarbonates  of  potassa,  soda,  and  ammonia  decompose  sulphate  of 
strontia  completely  at  the  common  temperature,  even  when  considerable 
quantities  of  alkaline  sulphates  are  present  (H.  Rose).  Boiling  pro- 
motes the  decomposition. 


Sr  O 51-75  56-40 

SO, 40-00  43-60 


91-75  100-00 

b.  Carbonate  of  strontia , artificially  prepared,  is  a white,  light,  loose 
powder.  It  dissolves,  at  the  common  temperature,  in  18045  parts  of 
water  (Expt.  No.  24).  Presence  of  ammonia  diminishes  its  solubility 
(Expt.  No.  25).  It  dissolves  pretty  readily  in  solutions  of  chloride  of 
ammonium  and  of  nitrate  of  ammonia,  but  is  precipitated  again  from 
these  solutions  by  ammonia  and  carbonate  of  ammonia,  and  more  com- 
pletely than  carbonate  of  baryta  under  similar  circumstances.  Water 
impregnated  with  carbonic  acid  dissolves  it  as  bicarbonate.  Its  reaction 
is  very  feebly  alkaline.  Alkaline  citrates  and  metaphosphates  impede 
the  precipitation  of  strontia  by  alkaline  carbonates.  Ignited  with  access 
of  air  it  is  infusible,  but  when  exposed  to  a most  intense  heat,  it  fuses, 
and  gradually  loses  its  carbonic  acid.  On  ignition  with  charcoal,  caustic 
strontia  is  formed,  with  evolution  of  carbonic  oxide  gas. 


Sr  O.... 

51-75 

70-17 

C 02  .... 

22-00 

29-83 

73-75 

100-00 

§73. 

3.  Lime. 

Lime  is  weighed  either  as  sulphate  of  lime,  or  as  carbonate  of  lime  ; 
to  convert  it  into  the  latter  form,  it  is  first  usually  precipitated  as  oxa- 
late of  lime. 

a.  Artificially  prepared  anhydrous  sulphate  of  lime  is  a loose,  white 
power.  It  dissolves,  at  the  common  temperature,  in  430  parts,  at  100°, 
in  460  parts  of  water  (Poggiale).  Presence  of  hydrochloric  acid,  nitric 


BASES  OF  GROUP  II. 


109 


§73.1 

acid,  chloride  of  ammonium,  sulphate  of  soda,  and  chloride  of  sodium, 
increases  its  solubility.  It  dissolves  with  comparative  ease,  especially 
on  gently  warming,  in  aqueous  solution  of  hyposulphite  of  soda  (Diehl). 
The  aqueous  solution  of  sulphate  of  lime  does  not  alter  vegetable  colors. 
In  alcohol  and  in  spirit  of  wine  of  90  per  cent,  it  is  almost  absolutely 
insoluble.  Exposed  to  the  air,  it  slowly  absorbs  water.  It  remains  un- 
altered at  a dull  red  heat.  Heated  to  intense  bright  redness,  it  fuses 
without  undergoing  decomposition.  At  a white  heat  it  loses  sulphuric 
acid  and  its  weight  is  considerably  diminished — the  residue  has  an  alka- 
line reaction  (Al.  Mitscherlich  *).  On  ignition  with  charcoal  or  under 
the  influence  of  reducing  gases  it  is  converted  into  sulphide  of  calcium. 
Solutions  of  alkaline  carbonates  and  bicarbonates  decompose  sulphate  of 
lime  more  readily  still  than  sulphate  of  strontia. 


CaO 28  41*18 

S 03 40  58*82 


68  100*00 

b.  Artificially  prepared  carbonate  of  lime  is  a fine  white  powder.  It 
dissolves  in  10601  parts  of  cold,  and  in  8834  parts  of  boiling  water 
(Expt.  Ho.  26).  The  solution  has  a barely  perceptible  alkaline  reaction. 
In  water  containing  ammonia  and  carbonate  of  ammonia,  it  dissolves 
much  more  sparingly,  one  part  of  the  salt  requiring  about  65000  parts 
(Expt.  No.  27)  ; this  solution  is  not  precipitated  by  oxalate  of  ammonia. 
Presence  of  chloride  of  ammonium  and  of  nitrate  of  ammonia  increases 
the  solubility  of  carbonate  of  lime  ; but  the  salt  is  precipitated  again 
from  these  solutions  by  ammonia  and  carbonate  of  ammonia,  and  more 
completely  than  carbonate  of  baryta  under  similar  circumstances. 
Neutral  salts  of  potassa  and  soda  likewise  increase  its  solubility.  The 
precipitation  of  lime  by  alkaline  carbonate  is  completely  prevented  or 
considerably  interfered  with  by  the  presence  of  alkaline  citrates  (Spil- 
ler)  or  metaphosphates  (Rube).  Water  impregnated  with  carbonic 
acid  dissolves  carbonate  of  lime  as  bicarbonate.  Carbonate  of  lime  re- 
mains unaltered  in  the  air,  at  100°,  and  even  at  a low  red  heat;  but 
upon  the  application  of  a stronger  heat,  more  particularly  with  free  ac- 
cess of  air,  it  gradually  loses  its  carbonic  acid.  By  means  of  a gas 
blowpipe-lamp,  carbonate  of  lime  (about  0*5  gran.),  in  an  open  platinum 
crucible,  is  without  difficulty  reduced  to  the  caustic  state  ; attempts  to 
effect  complete  reduction  over  a spirit  lamp  with  double  draught  have, 
however,  failed  (Expt.  No.  28).  It  is  decomposed  far  more  readily 
when  mixed  with  charcoal  and  heated  to  redness,  giving  off  its  car- 
bonic acid  in  the  form  of  carbonic  oxide. 


Ca  0 28  56*00 

CO, 22  44*00 


50  100*00 

c.  Oxalate  of  lime , precipitated  from  hot  or  concentrated  solutions,  is 
a fine  white  powder  consisting  of  extremely  minute  indistinct  crystals,  and 
almost  absolutely  insoluble  in  water.  If  the  oxalic  acid  is  held  to  be 


* Journ.  f.  prakt.  Chem. , 83,  485. 


110 


FORMS. 


[§  74. 

bibasic,  the  salt  has  the  formula,  2 CaO,  C4  06  -f  2 aq.  When  precipi- 
tated from  cold,  extremely  dilute  solutions,  the  salt  presents  a more 
distinctly  crystalline  appearance,  and  consists  of  a mixture  of  2 CaO, 
C4  06  *f-  2 aq.  and  2 CaO,  C4  06  + 6 aq.  (Souchay  and  Lenssen). 
Presence  of  free  oxalic  acid  and  acetic  acid  slightly  increases  the  solu- 
bility of  oxalate  of  lime.  The  stronger  acids  (hydrochloric  acid,  nitric 
acid)  dissolve  it  readily ; from  these  solutions  it  is  precipitated  again, 
unaltered,  by  alkalies  ; and  also  (provided  the  excess  of  acid  be  not  too 
great)  by  alkaline  oxalates  or  alkaline  acetates  added  in  excess.  Oxa- 
late of  lime  does  not  dissolve  in  solutions  of  chloride  of  potassium, 
chloride  of  sodium,  chloride  of  ammonium,  chloride  of  barium,  chloride 
of  calcium,  and  chloride  of  strontium,  even  though  these  solutions  be 
hot  and  concentrated ; but,  on  the  other  hand,  it  dissolves  readily  and 
in  appreciable  quantities,  in  hot  solutions  of  the  salts  belonging  to  the 
magnesia  group.  From  these  solutions  it  is  reprecipitated  by  an  excess 
of  alkaline  oxalate  (Souchay  and  Lenssen).  Alkaline  citrates  (Spiller) 
and  metaphosphates  (Rube)  impede  the  precipitation  of  lime  by  alka- 
line oxalates.  When  treated  with  solutions  of  many  of  the  heavy  me- 
tals, e.g .,  with  solution  of  chloride  of  copper,  nitrate  of  silver,  &c., 
oxalate  of  lime  suffers  decomposition,  a soluble  salt  of  lime  being 
formed,  and  an  oxalate  of  the  heavy  metallic  oxide,  which  separates  imme- 
diately, or  after  some  time  (Reynoso).  Oxalate  of  lime  is  unalterable 
in  the  air,  and  at  100°.  Dried  at  the  latter  temperature,  it  has  inva- 
riably the  following  composition  (Expt.  No.  29,  and  also  Souchay  and 
Lenssen  *) : 


2 CaO 56  38*36 

C4  06 72  49*32 

2 aq 18  12*32 


146  100*00 

At  205°  oxalate  of  lime  loses  its  water,  without  undergoing  decom- 
position ; at  a somewhat  higher  temperature,  still  scarcely  reaching  dull 
redness,  the  anhydrous  salt  is  decomposed,  without  actual  separation  of 
carbon,  into  carbonic  oxide  and  carbonate  of  lime.  The  powder,  which 
was  previously  of  snowy  whiteness,  transiently  assumes  a gray  color  in 
the  course  of  this  process,  even  though  the  oxalate  be  perfectly  pure. 
Upon  continued  application  of  heat,  this  gray  color  disappears  again. 
If  the  oxalate  of  lime  is  heated  in  small  coherent  fragments,  such  as 
are  obtained  upon  drying  the  precipitated  salt  on  a filter,  the  com- 
mencement and  progress  of  the  decomposition  can  be  readily  traced  by 
this  transient  appearance  of  gray.  If  the  process  of  heating  be  conducted 
properly,  the  residue  will  not  contain  a trace  of  caustic  lime.  Hy- 
drated oxalate  of  lime  exposed  suddenly  to  a dull  red  heat,  is  decom- 
posed with  considerable  separation  of  carbon. 

§ 74. 

4.  Magnesia. 

Magnesia  is  weighed  as  sulphate  of  magnesia,  pyrophosphate  of 


* Anna!,  der  Chem.  und  Pharm.,  100,  322. 


BASES  OF  GROUP  II. 


Ill 


§74.] 

magnesia,  or  pure  magnesia.  To  convert  it  into  the  pyrophosphate,  it 
is  precipitated  as  phosphate  of  ammonia  and  magnesia. 

<x.  Anhydrous  sulphate  of  magnesia  is  a white  opaque  mass.  It  dis- 
solves readily  in  water.  It  is  nearly  altogether  insoluble  in  absolute 
alcohol,  but  it  is  somewhat  soluble  in  spirit  of  wine.  It  does  not 
alter  vegetable  colors.  Exposed  to  the  air,  it  absorbs  water  rapidly. 
At  a moderate  red  heat,  it  remains  unaltered  ; but  when  heated  to  in- 
tense redness,  it  undergoes  partial  decomposition,  losing  part  of  its  acid, 
after  which  it  is  no  longer  perfectly  soluble  in  water.  By  means  of  a 
blast-lamp,  it  is  tolerably  easy  to  expel  the  whole  of  the  sulphuric  acid 
from  small  quantities  of  sulphate  of  magnesia  (Expt.  No.  30).  Ignited 
with  chloride  of  ammonium,  sulphate  of  magnesia  is  not  decomposed. 


Mg  0 20  33-33 

S 03 40  66-67 


60  100-00 

h.  Phosphate  of  magnesia  and  ammonia  is  commonly  a white  crystal- 
line powder.  [Sometimes  it  appears  as  a scaly' precipitate  with  pearly  lus- 
tre, sometimes  in  acicular  crystals.]  It  dissolves,  at  the  common  tem- 
perature, in  15293  parts  of  cold  water  (Expt.  No.  31).  In  water  con- 
taining ammonia,  it  is  much  more  insoluble — one  part  of  the  salt  re- 
quiring about  45000  parts  of  the  solvent  (Expt.  No.  32).  Chloride  of 
ammonium  slightly  increases  its  solubility  (Expt.  Nos.  34  and  35). 
Presence  of  alkaline  phosphates  exercises  no  influence  in  this  respect. 
It  dissolves  readily  in  acids,  even  in  acetic  acid.  Its  composition  is  ex- 
pressed by  the  formula 

2 Mg  O,  N H4  0,P05+  12  aq. 

10  eq.  of  water  escape  at  100°,  the  remaining  2,  together  with  the 
ammonia,  at  a red  heat,  leaving  2 Mg  O,  P 05.  The  change  of  the  or- 
dinary phosphoric  to  pyrophosphoric  acid,  is  indicated  by  a vivid  incan- 
descence of  the  whole  mass. 

If  phosphate  of  magnesia  and  ammonia  is  dissolved  in  dilute  hydro- 
chloric or  nitric  acid,  and  ammonia  be  then  added  to  the  solution,  the 
salt  is  reprecipitated  completely,  or  more  correctly,  only  so  much  remains 
in  solution  as  corresponds  to  its  ordinary  solubility  in  water  containing 
ammonia  and  ammoniacal  salt  (Expt.  No.  33). 

e.  Pyrophosphate  of  magnesia  presents  the  appearance  of  a white 
mass,  often  slightly  inclining  to  gray.  It  is  barely  soluble  in  water,  but 
readily  so  in  hydrochloric  acid,  and  in  nitric  acid.  It  remains  unal- 
tered in  air,  and  at  a red  heat ; at  a very  intense  heat  it  fuses  unaltered. 
Exposed  at  a white  heat  to  the  action  of  hydrogen,  3 Mg  O,  P 05  is 
formed,  while  P Hs,  P and  P 03  escape.  3 (2  Mg  O,  P 05)=2  (3  Mg 
O,  P 05)  -f  P 05  (Struve  *).  It  leaves  the  color  of  moist  turmeric-, 
and  of  reddened  litmus-paper  unchanged. 

If  we  dissolve  pyrophosphate  of  magnesia  in  hydrochloric  or  nitric 
acid,  add  water  to  the  solution,  boil  for  some  time,  and  then  precipitate 
with  ammonia  in  excess,  we  obtain  a precipitate  of  phosphate  of  mag- 
nesia and  ammonia  which,  after  ignition,  affords  less  2 Mg  O,  P 06,  than 


* Joum.  f.  prakt.  Chem.,  79,  349. 


112 


FORMS. 


was  originally  employed.  Weber  gives  the  loss  as  from  1*3  to  2*3  per 
cent.  My  own  experiments  (No.  36)  confirm  this  statement,  and  point 
out  the  circumstances  under  which  the  loss  is  the  least  considerable. 
By  long-continued  fusion  with  mixed  carbonates  of  potassa  and  soda,  py- 
rophosphate of  magnesia  is  completely  decomposed,  the  phosphoric  acid 
being  reconverted  into  the  tribasic  state.  If,  therefore,  we  treat  the 
fused  mass  with  hydrochloric  acid,  and  then  add  water  and  ammonia,  we 
re-obtain  on  igniting  the  precipitate  the  whole  quantity  of  the  salt  used. 


2 Mg  O 40-00  36-04 

P 05 71-00  63-96 


111-00  100-00 

d.  Pure  magnesia  is  a white,  light,  loose  powder.  It  dissolves  in 
55368  parts  of  cold,  and  in  the  same  proportion  of  boiling  water 
(Expt.  No.  37).  Its  aqueous  solution  has  a very  slightly  alkaline  re- 
action. Magnesia  dissolves  in  hydrochloric  and  in  other  acids,  without 
evolution  of  gas.  Magnesia  dissolves  readily  and  in  quantity  in  solutions 
of  neutral  ammonia  salts,  and  also  in  solutions  of  chloride  of  potassium 
and  chloride  of  sodium  it  is  more  soluble  than  in  water  (Expt.  No.  38). 
Exposed  to  the  air,  it  slowly  absorbs  carbonic  acid  and  water.  Mag- 
nesia is  highly  infusible,  remaining  unaltered  at  a strong  red  heat,  and 
fusing  superficially  only  at  the  very  highest  temperature. 


Mg. 

12 

60-03 

O.. 

8 

39-97 

20 

100-00 

BASES  of  the  third 

GROUP. 

§ 75. 

1.  Alumina. 

Alumina  is  usually  precipitated  as  hydrate,  occasionally  as  basic 
acetate  or  basic  formiate,  and  is  always  weighed  in  the  pure  state. 

a.  Hydrate  of  alumina , recently  precipitated,  is  gelatinous ; it  in- 
variably retains  a minute  proportion  of  the  acid  with  which  the  alu- 
mina was  previously  combined,  as  well  as  of  the  alkali  which  has 
served  as  the  precipitant ; it  is  freed  with  difficulty  from  these  admix- 
tures by  repeated  washing.* 

Hydrate  of  alumina  is  insoluble  in  pure  water ; but  it  readily  dis- 
solves in  soda  and  potassa  ; it  is  sparingly  soluble  in  caustic  ammonia, 
and  altogether  insoluble  in  carbonate  of  ammonia ; presence  of  ammo- 
nical  salts  greatly  diminishes  its  solubility  in  caustic  ammonia  (Expt. 
No.  39).  The  correctness  of  this  statement  has  been  amply  confirmed 
by  Malaguti  and  Durocher  ; f and  also  by  experiments  made  by  my 
former  assistant,  Mr.  J.  Fuchs.  The  former  chemists  state  also  that 
when  a solution  of  alumina  is  precipitated  with  sulphide  of  ammonium, 
the  fluid  may  be  filtered  off  five  minutes  after,  without  a trace  of  alumina 
in  it.  Fuchs  did  not  find  this  to  be  the  case  (Expt.  No.  40). 


* See  page 


note 


f Ann.  de  Chim.  et  de  Phys. , 3 Ser.  16,  421. 


BASES  OF  GROUP  III. 


113 


§75.1 

Hydrate  of  alumina,  recently  precipitated,  dissolves  readily  in  hydro- 
chloric or  nitric  acid ; but  after  filtration,  or  after  having  remained  for 
some  time  in  the  fluid  from  which  it  has  been  precipitated,  it  does  not 
dissolve  in  these  acids  without  considerable  difficulty  and  long  digestion. 
Hydrate  of  alumina  shrinks  considerably  on  drying,  and  then  presents 
the  appearance  of  a hard,  transparent,  yellowish,  or  of  a white,  earthy 
mass.  When  heated  to  redness  it  loses  its  water,  and  this  loss  is  fre- 
quently attended  with  slight  decrepitation,  and  invariably  with  con- 
siderable diminution  of  bulk. 

b.  Alumina , prepared  by  heating  the  hydrate  to  a moderate  degree 
of  redness,  is  a loose  and  soft  mass  ; but  upon  the  application  of  a very 
intense  degree  of  redness,  it  concretes  into  small,  hard  lumps.  At  the 
most  intense  white  heat  it  fuses  to  a colorless  glass.  Ignited  alumina 
is  dissolved  by  dilute  acids  with  very  great  difficulty ; in  fuming  hydro- 
chloric acid  it  dissolves  upon  long-continued  digestion  in  a warm  place, 
slowly,  but  completely.  It  dissolves  tolerably  easily  and  quickly  by  first 
heating  with  a mixture  of  8 parts  of  concentrated  sulphuric  acid  and  3 
parts  of  water,  and  then  adding  water  (A.  Mitscherlich*).  Ignition 
in  a current  of  hydrogen  gas  leaves  it  unaltered.  By  fusion  with  bisul- 
phate of  potassa  it  is  rendered  soluble,  the  residue  dissolving  readily  in 
water.  Upon  igniting  alumina  with  chloride  of  ammonium,  chloride  of 
aluminium  escapes ; but  the  process  fails  to  effect  complete  volatilization 
of  the  alumina  (H.  Rose).  When  alumina  is  fused  at  a very  high  tem- 
perature, in  conjunction  with  ten  times  its  quantity  of  carbonate  of 
soda,  aluminate  of  soda  is  formed,  which  is  soluble  in  water  (R.  Rich- 
ter). Placed  upon  moist  red  litmus  paper,  pure  alumina  does  not 
change  the  color  to  blue. 


Al2 ...27-50  53*40 

Os .24-00  46-60 


51-50  100-00 


c.  If  to  the  solution  of  a salt  of  alumina,  carbonate  of  soda  or  carbon- 
ate of  ammonia  be  added,  till  the  resulting  precipitate  only  just  redis- 
solves on  stirring,  and  then  acetate  of  soda  or  acetate  of  ammonia 
poured  in  in  abundance  and  the  mixture  boiled  some  time,  the  alumina 
is  precipitated  almost  completely  as  basic  acetate  in  the  form  of  trans- 
parent flocks,  so  that  if  the  filtrate  be  boiled  with  chloride  of  ammonium 
and  ammonia  only  unweighable  traces  of  alumina  separate.  If  the 
quantity  of  acetate  of  soda  employed  be  too  small,  the  precipitate  ap- 
pears more  granular,  the  filtrate  would  then  contain  a larger  amount  of 
alumina.  The  precipitate  is  difficult  to  filter  or  wash.  In  washing  it 
it  is  best  to  use  boiling  water,  containing  a little  acetate  of  soda  or 
acetate  of  ammonia.  The  precipitate  is  readily  soluble  in  hydrochloric 
acid. 

d.  If,  instead  of  the  acetates  mentioned  in  c,  the  corresponding 
formiates  be  used,  a flocculent  voluminous  precipitate  of  basic  formiate 
of  alumina  is  obtained,  which  may  be  very  readily  washed  (Fr. 
Schulze|). 


*Joum.  f.  prakt.  Chem.,  81,  110.  f Chem.  CentralbL 1861,  & 

8 


in 


FORMS. 


§76. 

2.  Sesquioxide  of  Chromium. 

Sesquioxide  of  chromium  is  usually  precipitated  as  hydrate,  and 
always  weighed  in  the  pure  state. 

a.  Hydrated  sesquioxide  of  chromium , recently  precipitated  from  a 
green  solution,  is  greenish-gray,  gelatinous,  insoluble  in  water : it  dis- 
solves readily,  in  the  cold,  in  solutions  of  potassa  or  soda,  to  a dark  green 
fluid ; it  dissolves  also  in  the  cold,  but  rather  sparingly,  in  solution  of 
ammonia,  to  a bright  violet  red  fluid.  In  acids  it  dissolves  readily,  im- 
parting a dark  green  tint  to  the  fluid.  Presence  of  chloride  of  ammo- 
nium exercises  no  influence  upon  the  solubility  of  the  hydrate  in  ammo- 
nia. Boiling  effects  the  complete  separation  of  the  sesquioxide  from  its 
solutions  in  potassa,  soda,  or  ammonia  (Expt.  No.  41).  The  dried  hy- 
drate is  a greenish-blue  powder ; it  loses  its  water  at  a gentle  red  heat. 

b.  Sesquioxide  of  chromium , produced  by  heating  the  hydrate  to 
dull  redness,  is  a dark  green  powder  ; upon  the  application  of  a higher 
degree  of  heat  it  assumes  a lighter  tint,  but  suffers  no  diminution  of 
weight ; the  transition  from  the  darker  to  the  lighter  tint  is  marked  by 
a vivid  incandescence  of  the  powder.  The  feebly  ignited  sesquioxide  is 
difficultly  soluble  in  hydrochloric  acid,  and  the  strongly  ignited  ses- 
quioxide is  altogether  insoluble  in  that  acid.  Mixed  with  chloride  of 
ammonium,  and  exposed  to  a red  heat,  sesquioxide  of  chromium  remains 
unaltered ; it  suffers  no  alteration  when  ignited  in  a current  of  hydro- 
gen gas. 


Cr2  52*48  68*62 

03 24*00  31*38 


76*48  100*00  ' 


BASES  OF  THE  FOURTH  GROUP. 


§77. 

1.  Oxide  of  Zinc;' 

Zinc  is  weighed  in  the  form  of  oxide  or  sulphide  ; it  is  precipitated 
as  BASIC  CARBONATE,  Or  as  SULPHIDE. 

a.  Basic  carbonate  of  zinc , recently  precipitated,  is  white,  flocculent, 
nearly  insoluble  in  water — (one  part  requiring  44600  parts.  Expt.  No. 
42) — but  readily  soluble  in  potassa,  soda,  ammonia,  carbonate  of  ammo- 
nia, and  acids.  The  solutions  in  soda  or  potassa,  if  concentrated,  are 
not  altered  by  boiling ; but  if  dilute,  nearly  all  the  oxide  of  zinc  present 
is  thrown  down,  as  a white  precipitate.  From  the  solutions  in  ammo- 
nia and  carbonate  of  ammonia,  especially  if  they  are  dilute,  oxide  of 
zinc  likewise  separates  upon  boiling.  When  a neutral  solution  of  zinc 
is  precipitated  with  carbonate  of  soda  or  carbonate  of  potassa,  carbonic 
acid  is  evolved,  since  the  precipitate  formed  is  not  Zn  O,  C02,  but  con- 
sists of  a compound  of  hydrated  oxide  of  zinc  with  carbonate  of  zinc,  in 
varying  proportions,  according  to  the  degree  of  concentration  of  the 


§77.] 


BASES  OF  GROUP  IV. 


115 


solution,  and  to  the  mode  of  precipitation.  Owing  to  the  presence  and 
action  of  this  carbonic  acid,  part  of  the  oxide  of  zinc  remains  in  solu- 
tion ; if  filtered  cold,  therefore,  the  filtrate  gives  a precipitate  with  sul- 
phide of  ammonium. 

But  if  the  solution  is  precipitated  boiling,  and  kept  at  that  tempera- 
ture for  some  time,  the  precipitation  of  the  zinc  is  complete  to  the  ex- 
tent that  the  filtrate  is  not  rendered  turbid  by  the  addition  of  sulphide 
of  ammonium  ; still,  if  the  filtrate,  mixed  with  sulphide  of  ammonium,  be 
allowed  to  stand  at  rest  for  many  hours,  minute  and  almost  un weigh a- 
ble  flakes  of  sulphide  of  zinc  will  separate  from  the  fluid.  The  precip- 
itate of  carbonate  of  zinc,  obtained  in  the  manner  just  described,  may 
be  completely  freed  from  all  admixture  of  alkali  by  washing  with  hot 
water.  If  ammoniacal  salts  be  present,  the  precipitation  is  not  com- 
plete till  every  trace  of  ammonia  is  expelled.  If  the  solution  of  a zinc 
salt  is  mixed  with  carbonate  of  potassa  or  soda  in  excess,  the  mixture 
evaporated  to  dryness,  at  a gentle  heat,  and  the  residue  treated  with 
cold  water,  a perceptible  proportion  of  the  zinc  is  obtained  in  solution 
as  double  carbonate  of  zinc  and  potassa  or  soda ; but  if  the  mixture  is 
evaporated  to  dryness  at  boiling  heat,  and  the  residue  treated  with  hot 
water,  the  whole  of  the  zinc,  with  the  exception  of  an  extremely  minute 
proportion,  as  we  have  already  had  occasion  to  observe,  is  obtained  as 
carbonate  of  zinc. 

The  dried  basic  carbonate  of  zinc  is  a fine,  white,  loose  powder ; ex- 
posure to  a red  heat  converts  it  into  oxide  of  zinc. 

b.  Oxide  of  zinc,  produced  from  the  carbonate  by  the  application  of 
a red  heat,  is  a white  light  powder,  with  a slightly  yellow  tint.  When 
heated,  it  acquires  a yellow  color,  which  disappears  again  on  cooling. 
Upon  ignition  with  charcoal,  carbonic  oxide  gas  and  zinc  fumes  escape. 
By  igniting  in  a rapid  current  of  hydrogen  gas,  metallic  zinc  is  produced  ; 
whilst  by  igniting  it  in  a feeble  current  of  hydrogen  gas,  crystallized  ox- 
ide of  zinc  is  obtained  (St.  Claire  Deville).  In  this  case,  too,  a por- 
tion of  the  metal  is  reduced  and  volatilized.  Oxide  of  zinc  is  insoluble 
in  water.  Placed  on  moist  turmeric  paper,  it  does  not  change  the  color 
to  brown.  In  acids,  oxide  of  zinc  dissolves  readily  and  without  evolu- 
tion of  gas.  Ignited  with  chloride  of  ammonium,  fused  chloride  of  zinc 
is  produced,  which  volatilizes  with  very  great  difficulty,  if  the  air  is  ex- 
cluded; but  readily  and  completely  with  free  access  of  air,  and  with 
chloride  of  ammonium  fumes.  Mixed  with  a sufficiency  Qf  powdered 
sulphur  and  ignited  in  a stream  of  hydrogen,  the  corresponding  amount 
of  sulphide  is  obtained  (H.  Rose). 


Zn 32*53  80*26 

0 8-00  19-74 


40-53  100-00 

c.  Sulphide  of  zinc,  recently  precipitated,  is  a white,  loose  hydrate  (Zn 
S,  H O).  The  following  facts  should  here  be  mentioned  with  regard  to  its 
precipitation.*  Colorless  sulphide  of  ammonium  precipitates  dilute  solu- 
tions of  zinc,  but  only  slowly  ; yellow  sulphide  of  ammonium  does  not  pre- 
cipitate dilute  solutions  of  zinc  (1  : 5000)  at  all.  Chloride  of  ammonium 
favors  the  precipitation  considerably.  Free  ammonia  acts  so  as  to  keep  the 


* Journ.  f.  prakt.  Chem. , 82,  263. 


116 


FORMS. 


precipitate  somewhat  longer  in  suspension,  otherwise  it  exerts  no  injurious 
influence.  If  the  conditions  which  1 shall  lay  down  are  strictly  observed, 
oxide  of  zinc  may  be  precipitated  by  sulphide  of  ammonium  from  a solu- 
tion containing  only-g-g^y^-g-.  Hydrated  sulphide  of  zinc,  on  account 
of  its  slimy  nature,  easily  stops  up  the  pores  of  the  filter,  and  cannot 
therefore  be  washed  without  difficulty  on  a filter.  The  washing  is  best 
performed  by  using  water  containing  sulphide  of  ammonium,  and  con- 
tinually diminished  quantities  of  chloride  of  ammonium  (at  last  none) 
(see  Expt.  No.  43).  The  hydrate  is  insoluble  in  water,  in  caustic  alka- 
lies, alkaline  carbonates,  and  the  monosulphides  of  the  alkali  metals.  It 
dissolves  readily  and  completely  in  hydrochloric  and  in  nitric,  but  only 
very  sparingly  in  acetic  acid.  When  dried,  the  precipitated  sulphide  of 
zinc  is  a white  powder  ; at  100°  it  loses  half,  and  at  a red  heat  the  whole 
of  its  water.  During  the  latter  process  some  sulphuretted  hydrogen 
escapes,  and  the  remaining  sulphide  of  zinc  contains  an  admixture  of 
oxide  of  zinc.  By  roasting  in  the  air,  and  intense  ignition  of  the  resi- 
due, small  quantities  of  sulphide  of  zinc  may  be  readily  converted  into 
the  oxide. 

On  igniting  the  dried  sulphide  of  zinc,  mixed  with  powdered  sulphur, 
in  a stream  of  hydrogen,  the  pure  anhydrous  sulphide  is  obtained.  (H. 
Bose). 

Zn 32-53  67*03 

S 16-00  32-97 

48-53  100*00 

§ 78. 

2.  Protoxide  of  Manganese. 

Manganese  is  weighed  either  as  protosesquioxide,  as  sulphide,  or  as 
pyrophosphate.  With  the  view  of  converting  it  into  the  first  form,  it  is 
precipitated  as  protocarbonate,  hydrated  protoxide,  or  binoxide. 
Before  weighing  as  pyrophosphate  it  must  be  precipitated  as  ammonio- 
phosphate. 

a.  Carbonate  of  protoxide  of  manganese,  recently  precipitated,  is  white, 
fiocculent,  nearly  insoluble  in  pure  water,  but  somewhat  more  soluble  in 
water  impregnated  with  carbonic  acid.  Presence  of  carbonate  of  soda  or 
potassa  does  not  increase  its  solubility.  Becently  precipitated  carbonate 
of  protoxide  of  manganese  dissolves  pretty  readily  in  solution  of  chloride 
of  ammonium : it  is  owing  to  this  property  that  a solution  of  protoxide 
of  manganese  cannot  be  completely  precipitated  by  carbonate  of  potassa 
or  soda,  in  presence  of  chloride  of  ammonium  (or  any  other  ammoniacal 
salt),  until  the  latter  is  completely  decomposed.  If  the  precipitate,  while 
still  moist,  is  exposed  to  the  air,  or  washed  with  water  impregnated  with 
air,  especially  if  it  is  in  contact  with  carbonated  alkali,  it  slowly  assumes 
a dirty  brownish-white  color,  part  of  it  becoming  converted  into  hydrated 
protosesquioxide  of  manganese.  In  washing  the  precipitate,  we  often 
obtain  a turbid  filtrate.  If  the  latter  be  allowed  to  stand  for  some  time 
in  a warm  place,  the  manganese  separates  in  brown  flocks.  If  the  precipi- 
tate is  dried  out  of  contact  with  air,  it  forms  a delicate  white  powder, 
persistent  in  the  air  [2  (Mn  O,  C 02)  + aq.] ; but  when  dried  with  free 
access  of  air,  the  powder  is  of  a more  or  less  dirty-white  color.  When 
strongly  heated  with  access  of  air,  this  powder  first  turns  black,  and 


BASES  OF  GROUP  IV. 


117 


§78.] 

changes  subsequently  to  brown  protosesquioxide  of  manganese.  However, 
this  conversion  takes  some  time,  and  must  never  be  held  to  be  completed 
until  two  weighings,  between  which  the  precipitate  has  been  ignited 
again  with  free  access  of  air,  give  perfectly  corresponding  results.  On 
igniting  the  carbonate  of  manganese,  mixed  with  powdered  sulphur,  in  a 
stream  of  hydrogen,  sulphide  of  manganese  is  obtained  (H.  Rose). 

b.  Hydrated  protoxide  of  manganese , recently  thrown  down,  forms  a 
white,  flocculent  precipitate,  insoluble  in  water  and  in  the  alkalies,  but 
soluble  in  chloride  of  ammonium ; this  precipitate  immediately  absorbs 
oxygen  from  the  air,  and  turns  brown,  owing  to  the  formation  of  hydrated 
protosesquioxide  of  manganese.  On  drying  it  in  the  air,  a brown  pow- 
der (hydrated  protosesquioxide  of  manganese)  is  obtained,  which,  when 
heated  to  intense  redness,  with  free  access  of  air,  is  converted  into  pro- 
tosesquioxide of  manganese,  and  on  ignition  with  powdered  sulphur,  in  a 
stream  of  hydrogen,  is  converted  into  sulphide. 

c.  Protosesquioxide  of  manganese , artificially  produced,  is  a brown  pow- 
der. All  the  oxides  of  manganese  are  finally  converted  into  this  by  igni- 
tion in  the  air.  Each  time  it  is  heated  it  assumes  a darker  color,  but  its 
weight  remains  unaltered.  It  is  insoluble  in  water,  and  does  not  alter 
vegetable  colors.  Heated  to  redness  with  chloride  of  ammonium  it  is  con- 
verted into  protochloride  of  manganese.  When  heated  with  concentrated 
hydrochloric  acid,  it  dissolves  to  chloride  with  evolution  of  chlorine. 

(Mn3  04+4  H Cl=3  Mn  Cl-f  Cl  + 4 H O) 

On  ignition  with  powdered  sulphur  in  a stream  of  hydrogen  it  is  con- 
verted into  sulphide  (H.  Rose). 


Mn3  82*50  72-05 

04  32-00  27-95 


114-50  100-00 

d.  Pinoxide  of  manganese  is  often  produced  in  analysis  by  exposing  a 
concentrated  solution  of  nitrate  of  protoxide  of  manganese  to  a gradually 
increased  temperature.  At  140°  brown  flakes  separate,  at  155°  much 
nitric  acid  is  disengaged,  and  the  whole  of  the  manganese  separates  as  an- 
hydrous binoxide.  It  is  brownish  black  and  is  deposited  on  the  sides 
of  the  vessel,  with  metallic  lustre.  It  is  insoluble  in  weak  nitric  acid, 
but  dissolves  to  a small  amount  in  hot  and  concentrated  nitric  acid 
(Deville).  In  hydrochloric  acid  it  dissolves  with  evolution  of  chlorine, 
in  concentrated  sulphuric  acid  with  liberation  of  oxygen.  The  binoxide 
is  also  often  obtained  in  the  hydrated  condition  in  analytical  separations, 
thus  when  we  precipitate  a solution  of  protoxide  with  hypochlorite  of 
soda,  or,  after  addition  of  acetate  of  soda,  with  chlorine  in  the  heat.  The 
brownish-black  flocculent  precipitate  thus  obtained  is  apt  to  contain  alkali. 

e.  Sulphide  of  manganese , prepared  in  the  wet  way,  forms  a flesh- 
colored  precipitate.  I must  make  a few  remarks  with  reference  to  its 
precipitation.*  This  is  effected  but  incompletely  if  we  add  to  a pure 
manganese  solution  only  sulphide  of  ammonium,  no  matter  whether  it  be 
colorless  or  yellow,  while  it  is  perfectly  effected  if  chloride  of  ammo- 
nium be  used  in  addition.  A very  large  quantity  even  of  chloride  of 
ammonium  does  not  impede  the  precipitation ; the  presence  of  a large 


* Journ.  f.  prakt.  Chem.,  82,  265. 


118 


FORMS. 


[§  T9. 

quantity  of  free  ammonia  somewhat  interferes  with  the  completeness  of 
tlie  precipitation.  In  all  cases  we  must  allow  to  stand  at  least  24  hours, 
and  with  very  dilute  solutions  48  hours,  before  filtering.  The  yellow 
sulphide  of  ammonium  is  the  most  appropriate  precipitant.  In  the 
presence  of  chloride  of  ammonium  even  a large  excess  of  sulphide  of  am- 
monium is  uninjurious.  If  the  precipitation  is  conducted  as  directed, 
the  manganese  can  be  precipitated  from  solutions  which  contain  only 
roVo'o'o'  ^ie  protoxide.  If  the  flesh-colored  hydrated  sulphide  remains 
some  time  under  the  fluid  from  which  it  was  precipitated,  it  sometimes 
becomes  converted  into  the  green  anhydrous  sulphide.  This  appearance 
often  occurs  after  a few  hours  or  days,  sometimes  not  for  weeks.  In 
acids  (hydrochloric,  sulphuric,  acetic,  &c.)  the  hydrate  dissolves  with 
evolution  of  sulphuretted  hydrogen.  If  the  precipitate,  while  still  moist, 
is  exposed  to  the  air,  or  washed  with  water  impregnated  with  air,  its 
fleshy  tint  changes  to  brown,  hydrated  protosesquioxide  of  manganese 
being  formed,  together  with  a small  portion  of  sulphate  of  protoxide 
of  manganese.  Hence  in  washing  the  hydrate  we  always  add  some 
sulphide  of  ammonium  to  the  wash-water,  and  keep  the  filter  as  full  as 
possible  with  the  same.  We  guard  against  the  filtrate  running  through 
turbid,  by  adding  gradually  decreasing  quantities  of  chloride  of  ammo- 
nium to  the  wash-wat'er  (at  last  none).  (Expt.  No.  44.)  On  igniting 
the  precipitate  mixed  with  sulphur  in  a stream  of  hydrogen  the  anhy- 
drous sulphide  remains.  If  we  have  gently  ignited  during  this  process, 
the  product  is  light  green ; if  we  have  strongly  ignited,  it  is  dark  green 
to  black.  Neither  the  green  nor  the  black  sulphide  attracts  oxygen  or 
water  quickly  from  the  air  (H.  Hose). 


Mn 27-5  63-22 

S 16-0  36-78 


43-5  100-00 

[f.  Ammonio-pliosphate  of  manganese  is  at  first  a white,  semi-gelati- 
nous precipitate,  which,  on  standing  for  some  time  in  the  cold,  and  more 
speedily  at  the  boiling  point,  crystallizes  in  pale  rose-colored  pearly  scales. 
It  dissolves  easily  in  hydrochloric  or  nitric  acid,  but  is  almost  absolutely 
insoluble  in  boiling  water,  ammonia,  and  ammoniacal  salts,  and  may  be 
washed  with  facilitv.  Its  formula  is  : 

2 Mn  O,  N Il4  O,  P 05  2 H O. 

By  ignition  it  is  converted  into  pyrophosphate  of  manganese. 

g.  Pyrophosphate  of  manganese  is  a nearly  white  powder,  not  altered 
by  a full  red  heat  or  by  exposure  to  the  air. 

2 Mn  O 71  50 

P05 71  50 

142  100] 

§79. 

3.  Protoxide  of  Nickel. 

Nickel  is  precipitated  as  hydrated  protoxide,  hydrated  sesquioxide, 
and  as  sulphide.  It  is  weighed  in  the  form  of  protoxide. 

a.  Ilydrated  protoxide  of  nickel  forms  an  apple-green  precipitate, 


§80.] 


BASES  OF  GROUP  IV. 


119 


almost  absolutely  insoluble  in  water,  but  soluble  in  ammonia  and  carbo- 
nate of  ammonia.  From  these  solutions  it  is  completely  reprecipitated 
by  potassa  or  soda,  added  in  excess ; application  of  heat  promotes  the 
precipitation.  It  is  unalterable  in  the  air ; on  intense  ignition,  it  passes 
into  pure  anhydrous  protoxide. 

b.  Protoxide  of  nickel  is  a dirty  grayish-green  powder,  insoluble  in 
water,  but  readily  soluble  in  hydrochloric  acid.  It  does  not  affect  vege- 
table colors.  It  suffers  no  variation  of  weight  upon  ignition  with  free 
access  of  air.  It  is  easily  reduced  to  metallic  nickel  by  ignition  in 
hydrogen  gas.  , 


Ni 

29-5 

78-67 

0 

8-0 

21-33 

37-5 

100-00 

[c.  Hydrated  sesquioxide  of  nickel , thrown  down  by  caustic  soda  from 
solutions  of  nickel  which  have  been  mixed  with  solution  of  hypochlo- 
rite of  soda,  is  a black  precipitate  that  is  much  more  easily  washed  than 
the  hydrated  protoxide.  It  passes  into  protoxide  upon  ignition.] 

d.  Hydrated  sulphide  of  nickel , prepared  in  the  wet  way,  forms  a 
black  precipitate,  insoluble  in  water.  When  thrown  down  in  the  cold 
it  is  somewhat  soluble  in  sulphide  of  ammonium  containing  free  ammonia, 
the  supernatant  liquid  having  a brown  color.  The  cold  precipitated  sul- 
phide is  liable  to  oxidize  somewhat  on  the  filter  to  sulphate  of  nickel. 
[When  separated  from  boiling  solutions  by  sulphide  of  sodium,  as  is 
directed  § 110,  these  inconveniences  are  not  experienced.]  It  is  very 
sparingly  soluble  in  concentrated  acetic  acid,  somewhat  more  soluble  in 
hydrochloric  acid.  It  is  more  readily  soluble  still  in  nitric  acid,  but  its 
best  solvent  is  nitrohydrochloric  acid.  It  loses  its  water  upon  the  appli- 
cation of  a red  heat ; when  ignited  in  the  air,  it  is  transformed  into  a 
basic  compound  of  sesquioxide  of  nickel  with  sulphuric  acid.  Mixed 
with  sulphur  and  ignited  in  a stream  of  hydrogen,  a fused  mass  remains, 
of  pale-yellow  color  and  metallic  lustre.  This  consists  of  Ni2  S,  but  its 
composition  is  not  perfectly  constant  (H.  Rose). 

§80. 

4.  Protoxide  of  Cobalt. 

Cobalt  is  weighed  in  the  pure  metallic  state,  or  as  protoxide  ; or 

as  SULPHATE  OF  PROTOXIDE,  01*  as  NITRITE  OF  COBALT  AND  POTASSA. 
Besides  the  properties  of  these  substances,  we  have  to  study  here  also 
those  of  the  hydrated  protoxide,  of  the  hydrated  sesquioxide,  and 

of  the  SULPHIDE. 

a.  Hydrated  protoxide  of  cobalt. — IJpon  precipitating  a solution  of 
protoxide  of  cobalt  with  potassa,  a blue  precipitate  (a  basic  salt)  is  formed 
at  first,  which,  upon  boiling  with  potassa  in  excess,  excluded  from  con- 
tact of  air,  changes  to  light  red  hydrated  protoxide  of  cobalt ; if,  on  the 
contrary,  this  process  is  conducted  with  free  access  of  air,  the  precipitate 
becomes  discolored,  part  of  the  hydrated  protoxide  being  converted  into 
hydrated  sesquioxide.  The  hydrate,  prepared  in  this  way,  retains  a trace 
of  the  acid,  and,  even  after  the  most  thorough  washing  with  hot  water, 
also  a minute  amount  of  the  alkaline  precipitant  (Expt.  No.  46). 

Hydrated  protoxide  of  cobalt  is  insoluble  in  water,  and  also  in  potassa ; 


FORMS. 


120 


L§  80. 


it  dissolves  in  solutions  of  ammoniacal  salts ; when  dried  in  the  air  it 
absorbs  oxygen,  and  acquires  a brownish  color.  (See  b.) 

[6.  Protoxide  of  cobalt. — Hydrated  protoxide  of  cobalt,  when  ignited 
in  the  air  or  in  oxygen,  yields  a variable  mixture  of  protoxide  and  pro- 
tosesquioxide,  and  cannot  certainly  be  brought  to  a constant  composi- 
tion. If,  however,  it  be  intensely  ignited,  and  cooled  in  a stream  of  car- 
bonic acid,  it  leaves  pure  protoxide  of  cobalt  (Russel,*  Gauhe,!  Burton  J). 
The  protoxide  has  a light-brown  color,  is  but  slightly  hygroscopic,  and 
dissolves  in  hydrochloric  acid  without  evolving  chlorine. 


Co 29*50  78*67 

0 8*00  21*33 


37*50  100*00] 

[c.  Hydrated  sesquioxide  of  cobalt  is  thrown  down  from  solutions  of 
protosalts  of  cobalt  by  a mixture  of  potassa  and  hypochlorite  of  soda  as 
a brown-black  precipitate,  which  is  completely  insoluble  in  the  precipi- 
tants  and  in  hot  water,  and  may  be  washed  from  all  but  the  minutest 
traces  of  alkali  with  much  greater  ease  than  the  hydrated  protoxide. 
(See  d.)] 


Co3 88*5  73*44 

04 32*0  26*56 


120*5  100*00 


d.  Metallic  cobalt  is  obtained  from  any  and  all  its  oxides,  and  from 
the  nitrate  and  chloride  of  cobalt,  by  ignition  in  a current  of  hydrogen 
gas.  It  is  a grayish-black  magnetic  powder,  less  fusible  than  gold.  If 
the  reduction  has  been  effected  at  an  intense  red  heat,  the  metal  is  un- 
alterable in  the  air  ; if  at  a low  heat,  it  oxidizes  or  even  burns.  Metallic 
cobalt  does  not  decompose  water,  either  cold  or  boiling ; it  dissolves  in 
nitric  and  sulphuric  acids  to  the  corresponding  salts  of  protoxide. 

[Metallic  cobalt,  obtained  from  oxides  which  have  been  precipitated 
by  caustic  alkalies,  has  an  alkaline  reaction,  from  the  retention  by  the 
oxides  of  a trace  of  alkali.  This  alkali,  which  need  not  exceed  0*2-0 *3 
per  cent.,  may  be  removed  by  repeated  washings  of  the  metal  with  hot 
water.] 

e.  /Sulphide  of  cobalt , produced  in  the  wet  way,  forms  a black  precipi- 
tate, insoluble  in  water,  in  alkalies,  and  in  alkaline  sulphides.  When 
precipitated  cold,  and  exposed  moist  to  the  air,  it  oxidizes  to  sulphate. 
[If  the  precipitate  be  digested  hot,  or  made  with  hot  sulphide  of  sodium, 
as  directed  § 111,  it  washes  readily  and  without  danger  of  oxidation.] 
Sulphide  of  cobalt  is  but  sparingly  soluble  [if  precipitated  hot,  in- 
soluble] in  acetic  acid  and  in  dilute  mineral  acids,  more  readily  in  con- 
centrated mineral  acids,  and  most  readily  in  warm  nitro-hydrochlorie 
acid.  [Sulphide  of  cobalt  may  be  converted  into  sulphate  by  heating 
with  strong  nitric  acid.]  Mixed  with  sulphur  and  ignited  in  a stream 
of  hydrogen,  we  obtain  a product  of  uncertain  composition,  not  suited 
for  the  determination  of  cobalt  (H.  Rose). 

f Sulphate  of  protoxide  of  cobalt  crystallizes,  in  combination  with 

* Jour.  Chem.  Soc.  (2),  I.  51.  f Fres.  Zeitschrift,  IY.  55. 

I Private  communication. 


BASES  OF  GROUP  IV. 


121 


§ 81*1 

7 aq.,  slowly  in  oblique  rhombic  prisms  of  a fine  red  color.  The  crystals 
yield  the  whole  of  the  7 eq.  of  water  at  a moderate  heat,  and  are  con- 
verted into  a rose-colored  anhydrous  salt,  which  bears  the  application  of  a 
gentle  red  heat  for  a short  time  without  losing  acid.  It  dissolves  rather 
difficultly  in  cold,  but  more  readily  in  hot  water.  [By  strong  ignition 
in  an  atmosphere  of  carbonate  of  ammonia  it  may  be  reduced  to  metal- 
lic cobalt.] 


Co  O 37-5  48-39 

S03  40-0  51-61 


77-5  100-00 

g.  Nitrite  of  cobalt  and  potassa , which  is  easily  produced  by  mix- 
ing a solution  of  protoxide  of  cobalt  with  nitrite  of  potassa,  and  enough 
nitric  or  acetic  acid  to  liberate  some  nitrous  acid  and  make  the  liquid 
permanently  acid,  forms  a crystalline  precipitate  of  a fine  yellow  color, 
which  dissolves  to  a very  perceptible  amount  in  pure  water,  and  still 
more  copiously  in  water  containing  chloride  of  sodium  and  chloride  of 
ammonium.  In  rather  concentrated  solutions  of  salts  of  potassa  (KO, 
S03,  — K Cl,  — KO,N  05,  — K O,  A),  [containing  some  nitrite  of  po- 
tassa (Gauhe)  ],  it  is  insoluble  even  upon  boiling.*  The  presence  of  a 
small  proportion  of  free  acetic  acid  exercises  no  solvent  action  under  these 
circumstances.  The  precipitate  does  not  dissolve  in  alcohol  of  80  per 
cent. ; but  it  dissolves,  though  not  copiously,  in  boiling  water,  to  a red 
fluid.  Nitrite  of  cobalt  and  potassa  is  decomposed  with  difficulty  by 
solution  of  potassa,  but  readily  by  solution  of  soda,  or  by  baryta- water ; 
the  decomposition  is  attended  with  separation  of  brown  hydrated  ses- 
quioxide  of  cobalt  (A.  Stromeyer-J-).  [The  composition,  dried  at  100°, 
is  somewhat  variable  (Stromeyer,  Erdmann J). 

Co203  (?) 17-7—19-0 

KO 28-2  — 32-8 

N 15-8  — 17-8 

Water 3-9  — 5*8]. 

It  is  decomposed  by  ignition,  and  gives  protosesquioxide  of  cobalt  and 
potassa.  [In  presence  of  nickel  and  alkaline  earths  the  precipitate  con- 
tains nickel  (Erdmann)]. 


§ 81. 

5.  Protoxide  of  Iron;  and  6.  Sesquioxide  of  Iron. 

Iron  is  usually  weighed  in  the  form  of  sesquioxide,  occasionally  as  sul- 
phide. We  have  to  study  also  the  hydrated  sesquioxide,  the  succinate 

OF  THE  SESQUIOXIDE,  the  ACETATE  OF  THE  SESQUIOXIDE,  and  the  FOR  MI  ATE 
OF  THE  SESQUIOXIDE. 

a.  Hydrated  sesquioxide  of  iron , recently  prepared,  is  a reddish-brown 
precipitate,  insoluble  in  water,  in  the  alkalies,  and  inammoniacal  salts,  but 

[*  If  thrown  down  in  absence  of  free  acid  the  precipitate  has  a darker  color, 
and  is  soluble  to  a slight  degree  in  solution  of  acetate  of  potassa.] 
f Anna!  d.  Chem.  u.  Pharm..  96,  218. 

X Jour.  f.  prakt.  Chem.,  97,  385. 


122 


FORMS. 


[8*1. 

readily  soluble  in  acids ; the  process  of  drying  very  greatly  red  aces  the 
bulk  of  this  precipitate.  When  dry,  it  presents  the  appearance  of  a brown, 
hard  mass,  with  shining  conchoidal  fracture.  If  the  precipitant  alkali  is 
not  used  in  excess,  the  precipitate  contains  basic  salt ; on  the  other  hand, 
if  the  alkali  has  been  used  in  excess,  a portion  of  it  is  invariably  carried 
down,  in  combination  with  the  sesquioxide  of  iron, — on  which  account 
ammonia  alone  can  properly  be  used  in  analysis,  as  a precipitant  for  salts  of 
sesquioxide  of  iron.  Under  certain  circumstances,  for  instance,  by  pro- 
tracted heating  of  a solution  of  acetate  of  sesquioxide  of  iron  on  the 
water-bath  (which  turns  the  solution  from  blood-red  to  brick-red,  and 
makes  it  appear  turbid  by  reflected  light),  and  subsequent  addition  of 
some  sulphuric  acid  or  salt  of  an  alkali,  a reddish-brown  hydrate  is  pro- 
duced, which  is  insoluble  in  cold  acids,  even  though  concentrated,  and  is 
not  attacked  even  by  boiling  nitric  acid  (L.  Pean  de  St.  Gilles*). 

b.  The  hydrated  sesquioxide  of  iron  is,  upon  ignition,  converted  into 
the  anhydrous  sesquioxide.  If  the  hydrated  sequioxide  has  not  been  most 
carefully  and  thoroughly  dried,  the  small  solid  lumps, -though  dry  outside, 
retain  still  a portion  of  water  confined  within,  the  sudden  conversion  of 
that  water  into  steam,  upon  the  application  of  a red  heat,  will  cause  par- 
ticles of  the  sesquioxide  to  fly  about,  and  may  thus  lead  to  loss  of  substance. 
P ure  sesquioxide  of  iron,  when  placed  upon  moist  reddened  litmus  paper, 
does  not  change  the  color  to  blue.  It  dissolves  slowly  in  dilute,  but  more 
rapidly  in  concentrated  hydrochloric  acid  ; the  application  of  a moderate 
degree  of  heat  effects  this  solution  more  readily  than  boiling.  With  a 
mixture  of  8 parts  concentrated  sulphuric  acid  and  3 parts  water,  it 
behaves  in  the  same  manner  as  alumina. 

The  weight  of  the  sesquioxide  does  not  vary  upon  ignition  in  the  air ; 
when  ignited  together  with  chloride  of  ammonium,  sesquichloride  of  iron 
escapes.  Ignition  with  charcoal,  in  a closed  vessel,  reduces  it  more  or  less. 
Strongly  ignited  with  sulphur  in  a stream  of  hydrogen,  it  is  transformed 
into  protosulphide. 


Fe2  56  70-00 

03  24  30-00 


80  100-00 


c.  Sulphide  of  iron , produced  in  the  humid  way,  forms  a black  precipi- 
tate. The  following  facts  are  to  be  noticed  with  regard  to  its  precipita- 
tion.! Sulphide  of  ammonium  used  alone,  whether  colorless  or  yellow, 
precipitates  pure  neutral  solutions  of  protoxide  of  iron,  but  slowly  and 
imperfectly.  Chloride  of  ammonium  acts  very  favorably  ; a large  excess 
even  is  not  attended  with  incovenience.  Ammonia  has  no  injurious 
action.  It  is  all  the  same  whether  the  sulphide  of  ammonium  be  colorless 
or  light  yellow.  If  the  directions  given  are  observed,  iron  may  be  precipi- 
tated by  means  of  sulphide  of  ammonium  from  solutions  containing  only 
of  the  protoxide.  In  such  a case,  however,  it  is  necessary  to 
allow  to  stand  forty-eight  hours.  Since  the  precipitate  rapidly  oxidizes  in 
contact  with  air,  sulphide  of  ammonium  is  to  be  added  to  the  wash-water, 
and  the  filter  kept  full.  [By  keeping  the  precipitate  with  the  liquid 
near  the  boiling  point  for  a long  time  (48  hours),  adding  sulphide  of 


* Joum.  f.  prakt.  Chem.,  66,  137. 


f Ibid.,  82,  268. 


BASES  OF  GROUP  IV. 


123 


§31-] 

ammonium  from  time  to  time,  the  sulphide  of  iron  becomes  dense,  and 
may  be  washed  with  little  danger  of  oxidation.]  It  is  well  to  mix  a little 
chloride  of  ammonium  with  the  wash- water,  but  the  quantity  should  be 
continually  reduced,  and  the  last  water  used  should  contain  none.  In 
mineral  acids,  even  when  very  dilute,  the  hydrated  sulphide  dissolves 
readily.  Mixed  with  sulphur,  and  strongly  ignited  in  a stream  of  hydro- 
gen, anhydrous  protosulphide  remains  (H.  Hose). 


Fe 28  63-64 

S 16  36-36 


44  100-00 


d.  When  a neutral  solution  of  a salt  of  sesquioxide  of  iron  is  mixed 
with  a neutral  solution  of  an  alkaline  succinate,  a cinnamon-colored  pre- 
cipitate of  a brighter  or  darker  tint  is  formed ; this  is  succinate  of  ses- 
quioxide of  iron  (Fe2  03,  C8  H4  06).  It  results  from  the  nature  of  this 
precipitate,  that  its  formation  must  set  free  an  equivalent  of  acid  (suc- 
cinic acid,  if  the  succinate  of  ammonia  is  used  in  excess)  ; e.q.y  2 (Fe2 
03,  3 S 03)  + 3 (2  N H4  O,  C8  H4  Gfi)  + 2 H 0 = 2 (Fe2  0„  C8  H4  06)  + 
6 (N  H4  O,  S 03)  + 2 H O,  C8  II4  06.  The  free  succinic  acid  does  not 
exercise  any  perceptible  solvent  action  upon  the  precipitate  in  a cold  and 
highly  dilute  solution,  but  it  redissolves  the  precipitate  a little  more 
readily  in  a warm  solution.  The  precipitate  must  therefore  be  filtered 
cold,  if  we  want  to  guard  against  re-solution.  Succinate  of  sesquioxide 
of  iron  is  insoluble  in  cold,  and  but  sparingly  soluble  in  hot  water.  It 
dissolves  readily  in  mineral  acids.  Ammonia  deprives  it  of  the  greater 
portion  of  its  acid,  leaving  compounds  similar  to  the  hydrated  sesquioxide 
of  iron,  which  contain  from  18  to  30  eq.  Fe2  03  for  1 eq.  C8  H4  06  (Dop- 
ping).  Warm  ammonia  withdraws  the  acid  more  completely  than  cold 
ammonia. 

[e.  If  to  a hot  solution  of  a salt  of  sesquioxide  of  iron  carbonate  of 
soda  be  added  till  a slight  permanent  precipitate  is  formed,  and  this  be 
redissolved  by  a few  drops  of  hydrochloric  acid,  then  heated  to  boiling, 
and  crystals  of  acetate  of  soda  be  added,  the  whole  of  the  iron  will  be  pre- 
cipitated as  basic  acetate  of  sesquioxid'e.  The  success  of  this  operation 
depends  on  the  iron  solution  being  sufficiently  dilute,  the  free  acid  suffi- 
ciently neutralized,  and  the  acetate  of  soda  in  sufficient  quantity.  In- 
stead of  carbonate  and  acetate  of  soda  the  corresponding  salts  of  ammo- 
nia may  be  used.  The  precipitate  may  usually  be  filtered  off  and  washed 
without  any  iron  passing  into  the  filtrate ; sometimes,  however,  the  re- 
verse is  the  case.  It  is  best  to  filter  immediately,  and  to  use  boiling 
wash- water.  When  these  directions  are  followed,  the  precipitate  is  free 
from  alkali,  but  if  the  precipitate  is  digested  with  the  liquid,  it  fixes  al- 
kali and  becomes  more  difficult  to  work*  (Reichardt)]. 

f Instead  of  the  acetate  of  soda  or  ammonia  used  in  e,  the  correspond- 
ing formiates  may  be  used.  The  basic  formiate  of  sesquioxide  of  iron 
here  obtained  is  more  easily  washed  than  the  basic  acetate  (Fa. 
Schulze  f). 


* Fres.  Zeitschrift,  V.  63. 


f Chem.  Centralbl.,  1861,  3. 


124 


FORMS. 


[§  82. 


BASES  OF  THE  FIFTH  GROUP. 

§ 82. 

1.  Oxide  of  Silver. 

Silver  may  be  weighed  in  the  metallic  state,  as  chloride,  sulphide, 

or  CYANIDE. 

a.  Metallic  silver , obtained  by  the  ignition  of  salts  of  silver  with  or- 
ganic acids,  &c.,  is  a loose,  light,  white,  glittering  mass  of  metallic  lustre ; 
but,  when  obtained  by  reducing  chloride  of  silver,  &c.,  in  the  wet  way, 
by  the  agency  of  zinc,  it  is  a dull  gray  powder.  It  is  not  fusible  over 
a Berzelius’  lamp.  Ignition  leaves  its  weight  unaltered.  It  dissolves 
readily  and  completely  in  dilute  nitric  acid. 

b.  Chloride  of  silver , recently  precipitated,  is  white  and  curdy.  On 
shaking,  the  large  spongy  flocks  combine  with  the  smaller  particles,  so 
that  the  fluid  becomes  perfectly  clear.  This  result  is,  however,  only 
satisfactorily  effected,  when  the  flocks  have  been  produced  in  presence 
of  excess  of  silver  solution,  and  when  they  have  been  recently  precipi- 
tated (compare  G.  J.  Mulder*).  Chloride  of  silver  is  in  a very  high 
degree  insoluble  in  water  and  in  dilute  nitric  acid ; strong  nitric  acid, 
on  the  contrary,  does  dissolve  a trace.  Hydrochloric  acid,  especially  if 
concentrated  and  boiling,  dissolves  it  very  perceptibly.  On  sufficiently 
diluting  such  a solution  with  cold  water  the  chloride  of  silver  falls  out 
so  completely  that  the  filtrate  is  not  colored  by  sulphuretted  hydrogen. 
Chloride  of  silver  is  insoluble,  or  very  nearly  so,  in  concentrated  sul- 
phuric acid ; in  the  dilute  acid  it  is  as  insoluble  as  in  water.  In  a solu- 
tion of  tartaric  acid  chloride  of  silver  dissolves  perceptibly  on  warming  ; 
on  cooling,  however,  the  solution  deposits  the  whole,  or,  at  all  events, 
the  greater  part  of  it.  Aqueous  solutions  of  chlorides  (of  sodium,  po- 
tassium, ammonium,  calcium,  zinc,  &c.)  all  dissolve  appreciable  quan- 
tities of  chloride  of  silver,  especially  if  they  are  hot  and  concentrated. 
On  sufficient  dilution  with  cold  water  the  dissolved  portion  separates  so 
completely  that  the  filtrate  is  not  colored  by  sulphuretted  hydrogen. 
The  solutions  of  alkaline  and  alkaline  earthy  nitrates  also  dissolve  a 
little  chloride  of  silver.  The  solubility  in  the  cold  is  trifling ; in  the  heat, 
on  the  contrary,  it  is  very  perceptible.  A solution  of  nitrate  of  mercury 
dissolves  chloride  of  silver  to  a tolerable  extent ; alkaline  acetates  sepa- 
rate it  from  the  solution.  Chloride  of  silver  dissolves  readily  in  aque- 
ous ammonia,  and  also  in  the  solution  of  cyanide  of  potassium  and  that 
of  hyposulphite  of  soda.  Under  the  influence  of  light  the  chloride  of 
silver  soon  changes  to  violet,  finally  black,  losing  chlorine,  and  passing 
partly  into  Ag2  Cl.  The  change  is  quite  superficial,  but  the  loss  of 
weight  resulting  is  very  appreciable  (Mulder,  op.  cit.  p.  21).  On  long 
contact  (say  for  24  hours)  with  pure  water,  especially  if  hot  of  75°, 
chloride  of  silver,  although  removed  from  the  influence  of  light,  becomes 
gray,  and,  it  appears,  decomposed ; the  precipitate  is  found  to  contain 
oxide  of  silver,  and  the  water  hydrochloric  acid  (Mulder).  On  diges- 
tion with  excess  of  solution  of  bromide  or  iodide  of  potassium  the  chlo- 
ride of  silver  is  completely  transformed  into  bromide  or  iodide  of  silver, 
as  the  case  may  be  (Field  f).  On  drying,  chloride  of  silver  becomes 

* Die  Silberprobirmethode,  translated  into  German  by  D.  Chr.  Grimm,  pp.  19 
and  311.  Leipzig:  J.  J.  Weber.  1859. 

f Quart.  Journ.  of  Chem.  Soc.  x.  234;  Journ.  f.  prakt.  Chem.  73,  404. 


BASES  OF  GROUP  V. 


125 


§83.] 

pulverulent;  on  heating,  it  aoquires  a yellow  color;  at  260°  it  fuses  to 
a transparent  yellow  fluid,  which  on  cooling  presents  the  appearance  of 
a colorless  and  slightly  yellowish  mass.  At  a very  strong  heat  it  vola- 
tilizes unchanged.  It  may  be  readily  reduced  to  metallic  silver,  by  ig- 
niting it  in  a current  of  hydrogen  gas. 


Ag 107*97  75-28 

Cl 35-46  24-72 


143-43  100-00 

c.  Sulphide  of  silver , prepared  in  the  humid  way,  is  a black  precipi- 
tate, insoluble  in  water,  dilute  acids,  alkalies,  and  alkaline  sulphides. 
This  precipitate  is  unalterable  in  the  air ; after  being  allowed  to  sub- 
side, it  is  filtered  and  washed  with  ease,  and  may  be  dried  at  100°,  with- 
out suffering  decomposition.  It  dissolves  in  concentrated  nitric  acid, 
with  separation  of  sulphur.  Solution  of  cyanide  of  potassium  fails  to 
dissolve  sulphide  of  silver,  except  the  cyanide  be  used  greatly  in  excess. 
In  the  latter  case  it  dissolves  to  a slight  extent,  but  is  generally 
reprecipitated  on  addition  of  water  (Bechamp*).  Ignited  in  a current 
of  hydrogen,  it  passes  readily  and  completely  into  the  metallic  state  (H. 
Kose). 

Ag 107-97  87-07 

S 16-00  12-93 


123-97  100-00 

d.  Cyanide  of  silver , recently  thrown  down,  forms  a white  curdy  pre- 
cipitate insoluble  in  water  and  dilute  nitric  acid,  soluble  in  cyanide  of 
potassium  and  also  in  ammonia ; exposure  to  light  fails  to  impart  the 
slightest  tinge  of  black  to  it;  it  may  be  dried  at  100°  without  suffering 
decomposition.  Upon  ignition,  it  is  decomposed  into  cyanogen  gas, 
which  escapes,  and  metallic  silver,  which  remains,  mixed  with  a little 
paracyanide  of  silver.  By  boiling  with  a mixture  of  equal  parts  of  sul- 
phuric acid  and  water,  it  is,  according  to  Glassford  and  Napier,  dis- 
solved to  sulphate  of  silver,  with  liberation  of  hydrocyanic  acid. 


Ag 107-97  80-60 

CaN 26-00  19-40 


133-97  100-00 

§ 83- 

2.  Oxide  of  Lead. 

Lead  is  weighed  as  oxide,  sulphate,  chromate,  and  sulphide. 
Besides  these  compounds,  we  have  also  to  study  the  carbonate  and  the 
OXALATE. 

a.  Neutral  carbonate  of  lead  forms  a heavy,  white,  pulverulent  preci- 
pitate. It  i?  but  very  slightly  soluble  in  perfectly  pure  (boiled)  water 
(one  part  requiring  50550  parts,  see  Expt.  47,  a)  ; but  it  dissolves 


* Joum.  f.  prakt.  Cbera.  60,  04. 


126 


FORMS. 


somewhat  more  readily  in  water  containing  ammonia  and  ammoniacal 
salts  (comp.  Expt.  No.  47,  b and  c).  It  dissolves  also  somewhat  more 
readily  in  water  impregnated  with  carbonic  acid,  than  in  pure  water.  It 
loses  its  carbonic  acid  when  ignited. 

b.  Oxalate  of  lead  is  a white  powder,  very  sparingly  soluble  in  water. 
The  presence  of  ammonia  salts  slightly  increases  its  solubility  (Expt. 
No.  48).  When  heated  in  close  vessels,  it  leaves  suboxide  of  lead ; but 
when  heated,  with  access  of  air,  yellow  oxide  (protoxide). 

c.  Oxide , or  protoxide  of  lead , produced  by  igniting  the  carbonate  or 
oxalate,  is  a lemon-yellow  powder,  inclining  sometimes  to  a reddish  yel- 
low, or  to  a pale  yellow.  When  this  yellow  oxide  of  lead  is  heated,  it 
assumes  a brownish-red  color,  without  the  slightest  variation  of  weight. 
It  fuses  at  an  intense  red  heat.  Ignition  with  charcoal  reduces  it.  When 
exposed  to  a white  heat,  it  rises  in  vapor.  Placed  upon  moist  reddened 
litmus  paper,  it  changes  the  color  to  blue.  When  exposed  to  the  air, 
it  slowly  absorbs  carbonic  acid.  Mixed  with  chloride  of  ammonium  and 
ignited,  it  is  converted  into  chloride  of  lead.  Oxide  of  lead  in  a state 
of  fusion  readily  dissolves  silicic  acid  and  the  earthy  bases  with  which 
the  latter  may  be  combined. 


Pb 103-50  92-83 

O 8-00  7-17 


111-50  100-00 

d.  Sulphate  of  lead  is  a heavy  white  powder.  It  dissolves,  at  the 
common  temperature,  in  22800  parts  of  pure  water  (Expt.  No.  49) ; it  is 
less  soluble  still  in  water  containing  sulphuric  acid  (one  part  requiring 
36500  parts — Expt.  No.  50)  ; it  is  far  more  readily  soluble  in  water  con- 
taining ammoniacal  salts ; from  this  solution  it  may  be  precipitated  again 
by  adding  sulphuric  acid  in  excess  (Expt.  No.  51).  It  is  almost  entirely 
insoluble  in  alcohol  and  spirit  of  wine.  Of  the  salts  of  ammonia,  the 
nitrate,  acetate,  and  tartrate  are  more  especially  suited  to  serve  as  sol- 
vents for  sulphate  of  lead : the  two  latter  salts  of  ammonia  are  made 
strongly  alkaline  by  addition  of  ammonia,  previous  to  use  (Wacken- 
roder).  Sulphate  of  lead  dissolves  in  concentrated  hydrochloric  acid, 
upon  heating.  In  nitric  acid  it  dissolves  the  more  readily,  the  more 
concentrated  and  hotter  the  acid  ; water  fails  to  precipitate  it  from  its 
solution  in  nitric  acid ; but  the  addition  of  a copious  amount  of  dilute 
sulphuric  acid  causes  its  precipitation  from  this  solution.  The  more  nitric 
acid  the  solution  contains,  the  more  sulphuric  acid  is  required  to  throw 
down  the  sulphate  of  lead.  Sulphate  of  lead  dissolves  sparingly  in  con- 
centrated sulphuric  acid,  and  the  dissolved  portion  precipitates  again  upon 
diluting  the  acid  with  water  (more  completely  upon  addition  of  alcohol). 
A moderately  concentrated  solution  of  hyposulphite  of  soda  dissolves  the 
sulphate  of  lead  completely  even  if  cold,  more  readily  if  warmed  ; on  boil- 
ing, the  solution  becomes  black  from  separation  of  a small  quantity  of 
sulphide  of  lead  (J.  Lowe  *).  The  solutions  of  carbonates  and  bicar- 
bonates of  the  alkalies  convert  sulphate  of  lead,  even  at  the  common 
temperature,  completely  into  carbonate  of  lead.  The  solutions  of  the 
carbonates,  but  not  those  of  the  bicarbonates,  dissolve  some  oxide  of 
lead  in  this  process  (H.  Rose  |).  Sulphate  of  lead  dissolves  readily  in 


Joum.  f.  prakt.  Chem.  74,  348. 


f Pogg.  Annal.  95,  426. 


BASES  OF  GROUP  V. 


127 


§84.] 


hot  solutions  of  potassa  or  soda.  It  is  unalterable  in  the  air,  and  at  a 
gentle  red  heat ; when  exposed  to  a higher  degree  of  heat,  it  fuses 
without  suffering  decomposition  (Expt.  No.  52),  provided  always  the 
action  of  reducing  gases  be  completely  excluded — for,  if  this  is  not  the 
case,  the  weight  will  continually  diminish,  owing  to  the  reduction  of 
Pb  O,  S 03  to  Pb  S (Erdmann  *).  Fusion  with  cyanide  of  potassium 
reduces  the  whole  of  the  lead  to  the  metallic  state. 


PbO 111*50  73*60 

S03  40*00  26*40 


151*50  100*00 

e.  Sulphide  of  lead , prepared  in  the  wet  way,  is  a black  precipitate, 
insoluble  in  water,  dilute  acids,  alkalies,  and  alkaline  sulphides.  In  pre- 
cipitating it  from  a solution  containing  free  hydrochloric  acid,  it  is 
necessary  to  dilute  plentifully,  otherwise  the  precipitation  will  be  incom- 
plete. Even  if  a fluid  only  contain  2*5  per  cent.  H Cl,  the  whole  of  the 
lead  will  not  be  precipitated  (M.  Martin  f).  It  is  unalterable  in  the 
air ; it  cannot  be  dried  at  100°  without  suffering  decomposition.  Ac- 
cording to  H.  Pose  it  increases  perceptibly  in  weight  by  oxidation ; in 
the  case  of  long-protracted  drying  even  becoming  a few  per  cents, 
heavier.];  I have  confirmed  his  statement  (see  Expt.  No.  53).  If  sul- 
phate of  lead  mixed  with  sulphur  be  exposed  in  a current  of  hydrogen 
to  a good  red  heat,  pure  crystalline  Pb  S remains;  if  a less  heat  be 
employed,  the  residue  contains  excess  of  sulphur  (H.  Pose§).  [Accord- 
ing to  S ouch  ay,  ||  sulphide  of  lead  is  obtained  pure  by  ignition  with  excess 
of  sulphur  in  hydrogen,  if  only  the  lower  one-fourth  of  the  crucible  be 
heated  to  redness  for  5-10  minutes.  The  results  were  rather  too  low 
than  too  high.]  It  dissolves  in  concentrated  hot  hydrochloric  acid, 
with  evolution  of  sulphuretted  hydrogen.  In  moderately  strong  nitric 
acid,  sulphide  of  lead  dissolves,  upon  the  application  of  heat,  with  sepa- 
ration of  sulphur ; — if  the  acid  is  rather  concentrated,  a small  portion  of 
sulphate  of  lead  is  also  formed.  Fuming  nitric  acid  acts  energetically 
upon  sulphide  of  lead,  and  converts  it  into  sulphate  without  separation 
of  sulphur. 


Pb 103*50  86*61 

S 16*00  13*39 


119*50  100*00 


f.  For  the  composition  and  properties  of  chromate  of  lead,  see  chromic 
acid, , § 93,  2. 


§84. 


3.  Suboxide  of  Mercury;  and  4.  Oxide  of  Mercury. 


Mercury  is  weighed  either  in  the  metallic  state,  as  subchloride,  or 
as  sulphide,  or  occasionally  also  as  oxide. 

a.  Metallic  mercury , when  pure,  presents  a perfectly  bright  surface. 

* Joum.  f.  prakt.  Chem.  62,  381.  \ Journ.  f.  prakt.  Chem.  67,  374. 

X Pogg.  Anna!  91,  110  ; and  110,  134.  § Po gg.  Annal.  110,  135. 

||  [Fres.  Zeitschrift,  IV.  65.] 


128 


FORMS. 


[§  34. 

It  is  unalterable  in  the  air  at  the  common  temperature.  It  boils  at 
360°.  It  evaporates,  but  very  slowly,  at  summer  temperatures.  Upon 
long-continued  boiling  with  water,  a small  portion  of  mercury  volatilizes, 
and  traces  escape  along  with  the  aqueous  vapor,  whilst  a very  minute 
proportion  remains  suspended  (not  dissolved)  in  the  water  (comp.  Expt. 
No.  54).  This  suspended  portion  of  mercury  subsides  completely  after 
long  standing.  When  metallic  mercury  is  precipitated  from  a fluid,  in 
a very  minutely  divided  state,  the  small  globules  will  readily  unite  into 
a large  one  if  the  mercury  be  perfectly  pure ; but  even  the  slightest  trace 
of  extraneous  matter,  such  as  fat,  &c.,  adhering  to  the  mercury  will  pre- 
vent the  union  of  the  globules.  Mercury  does  not  dissolve  in  hydro- 
chloric acid,  not  even  in  concentrated  ; it  is  barely  soluble  in  dilute  cold 
sulphuric  acid,  but  dissolves  readily  in  nitric  acid,  and  in  boiling  con- 
centrated sulphuric  acid. 

b.  Subchloride  of  mercury , prepared  in  the  wet  way,  is  a heavy  white 
powder.  It  is  almost  absolutely  insoluble  in  cold  water  ; in  boiling  water 
it  is  gradually  decomposed,  the  water  taking  up  chlorine  and  mercury ; 
upon  continued  boiling,  the  residue  acquires  a gray  color.  Highly  dilute 
hydrochloric  acid  fails  to  dissolve  subchloride  of  mercury  at  the  common 
temperature,  but  dissolves  it  slowly  at  a higher  temperature  ; upon  ebulli- 
tion, with  access  of  air,  the  whole  of  the  subchloride  is  gradually  dissolved 
by  the  dilute  acid:  the  solution  contains  chloride  of  mercury  (Hg2  Cl  fi- 
ll Cl -f-0=2  Hg  C14-H  O).  Subchloride  of  mercury,  when  acted  upon 
by  boiling  concentrated  hydrochloric  acid,  is  rather  speedily  decomposed 
into  mercury,  which  remains  undissolved,  and  chloride  of  mercury,  which 
dissolves.  Boiling  nitric  acid  dissolves  subchloride  of  mercury,  and  con- 
verts it  into  chloride  and  nitrate  of  mercury.  Chlorine  water  and  nitro- 
hydrochloric  acid  dissolve  it  to  chloride,  even  in  the  cold.  Solutions  of 
/alkaline  chlorides  decompose  subchloride  of  mercury  into  metallic  mer- 
cury and  chloride  of  mercury,  which  latter  dissolves ; at  a low  tempera- 
ture, this  decomposition  is  confined  to  a small  portion  of  the  subchloride, 
but  the  application  of  heat  promotes  the  decomposing  action  of  these 
solutions.  Subchloride  of  mercury  does  not  affect  vegetable  colors  ; it  is 
unalterable  in  the  air,  and  may  be  dried  at  100°,  without  suffering  any 
diminution  of  weight ; when  exposed  to  a higher  degree  of  heat,  though 
still  below  redness,  it  volatilizes  completely,  without  previous  fusion. 


Hg2  200-00  84-94 

Cl  35-46  15-06 


235-46  100-00 

c.  Sulphide  of  mercury , prepared  in  the  wet  way,  is  a black  powder, 
insoluble  in  water.  Dilute  hydrochloric  and  dilute  nitric  acid  fail  to 
dissolve  it,  and  it  remains  insoluble  even  in  boiling  hydrochloric  acid  ; it 
is  only  very  slightly  soluble  in  hot  concentrated  nitric  acid,  but  it  dis- 
solves readily  in  nitrohydrochloric  acid.  From  a solution  of  chloride  of 
mercury,  containing  much  free  hydrochloric  acid,  the  whole  of  the  metal 
cannot  be  precipitated  by  means  of  sulphuretted  hydrogen,  as  Hg  S, 
until  the  solution  is  properly  diluted.  Should  such  a solution  be  very 
concentrated,  subchloride  of  mercury  and  sulphur  are  precipitated  (M. 
Martin*).  Solution  of  potassa,  even  boiling,  fails  to  dissolve  it.  It 


* Joum.  f.  prakt.  Chem.  67,  376. 


§85.1 


BASES  OF  GROUP  V. 


129 


dissolves  in  sulphide  of  potassium,  but  readily  only  in  presence  of 
free  alkali  (Expt.  No.  55).  Sulphide  of  ammonium,  cyanide  of  potas- 
sium, and  sulphite  of  soda  do  not  dissolve  it.  On  account  of  the  solu- 
bility of  sulphide  of  mercury  in  sulphide  of  potassium,  it  is  impossible  to 
precipitate  mercury  by  means  of  sulphide  of  ammonium  completely  from 
solutions  containing  hydrate  or  carbonate  of  potassa  or  soda.  In  the  air 
it  is  unalterable,  even  in  the  moist  state,  and  at  100°.  When  exposed 
to  a higher  temperature,  it  sublimes  completely  and  unaltered. 


Hg 100-00  86-21 

S 16-00  13-79 


116-00  100-00 

d.  Oxide  of  mercury , prepared  in  the  dry  way,  is  a crystalline  brick- 
colored  powder,  which,  when  exposed  to  the  action  of  heat,  changes  to  the 
color  of  cinnabar,  and  subsequently  to  a violet-black  tint.  It  bears  a 
tolerably  strong  heat  without  suffering  decomposition ; but,  when  heated 
to  incipient  redness,  it  is  decomposed  into  mercury  and  oxygen ; perfect- 
ly pure  oxide  of  mercury  leaves  no  residue  upon  continued  exposure  to 
a red  heat.  The  escaping  fumes  also  should  not  redden  litmus  paper. 
Water  takes  up  a trace  of  oxide  of  mercury,  acquiring  thereby  a very 
weak  alkaline  reaction.  Hydrochloric  or  nitric  acid  dissolves  it  readily. 


Hg.. 100-00  92-59 

O 8-00  7-41 


108-00  100-00 

§ 85. 

5.  Oxide  of  Copper. 

Copper  is  usually  weighed  in  the  metallic  state,  or  in  the  form  of 
oxide,  or  of  subsulphide.  Besides  these  forms,  we  have  to  examine  the 
sulphide,  the  suboxide,  and  the  subsulphocyanide. 

a.  Copper  fuses  only  at  a white  heat.  . Exposure  to  dry  air,  or  to 
moist  air,  free  from  carbonic  acid,  leaves  the  fused  metal  unaltered ; but 
upon  exposure  to  moist  air  impregnated  with  carbonic  acid,  it  becomes 
gradually  tarnished  and  coated  with  a film,  first  of  a blackish-gray,  finally 
of  a bluish-green  color.  Precipitated  finely  divided  copper,  in  contact 
with  water  and  air,  oxidizes  far  more  quickly,  especially  at  an  elevated 
temperature.  On  igniting  copper  in  the  air,  a layer  of  black  oxide  forms  on 
its  surface.  Hydrochloric  acid  fails  to  dissolve  it,  even  upon  boiling,  if  the 
air  is  excluded ; but  with  free  access  of  air  it  dissolves  it  slowly.  Copper 
dissolves  readily  in  nitric  acid.  In  ammonia  it  dissolves  slowly  if  free 
access  is  given  to  the  air  ; but  it  remains  insoluble  in  that  menstruum  if 
the  air  is  excluded.  Metallic  copper  brought  into  contact  in  a closed  vessel 
with  solution  of  chloride  of  copper  in  hydrochloric  acid,  or  with  an  ammo- 
niacal  solution  of  oxide  of  copper,  reduces  the  chloride  to  subchloride,  or 
the  oxide  to  suboxide,  an  equivalent  of  metal  being  dissolved  for  every 
equivalent  of  chloride  or  oxide. 

b.  Oxide  of  copper. — If  a dilute,  cold,  aqueous  solution  of  a salt  of 
oxide  of  copper  is  mixed  with  solution  of  potassa  or  soda  in  excess,  a 

9 


130 


FORMS. 


[§  85. 

light  blue  precipitate  of  hydrated  oxide  of  copper  (Cu  O,  H O)  is 
formed,  which  is  difficult  to  wash.  If  the  precipitate  be  left  in  the  fluid 
from  which  it  has  been  precipitated,  it  will  gradually  become  brownish 
black,  and  pass  into  3 Cu  O,  H O (Harms*). 

This  transformation  is  immediate  upon  heating  the  fluid  nearly  to 
boiling.  The  fluid  filtered  off  from  the  black  precipitate  is  free  from 
copper.  If  the  solutions  in  question  are  mixed  in  a concentrated  state, 
in  addition  to  the  formation  of  the  blue  precipitate,  the  fluid  itself  ac- 
quires a blue  color,  owing  to  a portion  of  very  minutely  divided  hy- 
drated oxide  remaining  suspended  in  it.  From  a fluid  of  this  descrip- 
tion protracted  boiling  will  fail  to  precipitate  all  the  copper ; after  dilu- 
tion with  water,  the  object  is  readily  attained.  If  a solution  of  a salt 
of  copper  contains  non-volatile  organic  substances,  the  addition  of  al- 
kali in  excess  will,  even  upon  boiling,  fail  to  precipitate  the  whole  of  the 
copper  as  oxide.  The  hydrate  (3  Cu  O,  H O)  precipitated  with  potassa  or 
soda  from  hot  dilute  solutions  may  be  completely  freed  from  the  preci- 
pitant by  washing  with  boiling  water.  Oxide  of  copper,  prepared  by 
igniting  the  hydrate  or  carbonate  or  nitrate  of  copper,  is  a brownish- 
black,  or  black  powder,  which  remains  unaltered  upon  strong  ignition 
over  the  gas-  or  spirit-lamp,  provided  all  reducing  gases  be  excluded 
(Expt.  No.  59).  It  is  very  readily  reduced  by  ignition  with  charcoal, 
or  reducing  gases  ; heated  in  the  air,  the  reduced  copper  re-oxidizes. 
Mixed  with  sulphur  and  ignited  in  a current  of  hydrogen,  towards  the  end 
strongly,  the  oxide  of  copper  passes  into  subsulphide  (Cu2  S;  H.  Rose). 
Oxide  of  copper,  in  contact  with  the  atmosphere,  absorbs  water ; oxide 
that  has  been  but  slightly  ignited  absorbs  the  water  more  rapidly  than  such 
as  has  been  strongly  ignited  (Expt.  No.  57).  Oxide  of  copper  is  nearly 
insoluble  in  water ; but  it  dissolves  readily  in  hydrochloric  acid,  nitric 
acid,  &c. ; less  readily  in  ammonia.  It  does  not  affect  vegetable  colors. 


Cu 31*70  79-85 

O 8-00  20-15 


39-70  100-00 

c.  Sulphide  of  copper , prepared  in  the  wet  way,  is  a brownish-black, 
or  black  precipitate,  almost  absolutely  insoluble  in  water ; f when  the 
recently  prepared  precipitate,  in  a moist  state,  is  exposed  to  the  air,  it 
acquires  a greenish  tint  and  the  property  of  reddening  litmus  paper, 
sulphate  of  copper  being  formed.  Hence  it  must  be  washed  with  water 
containing  sulphuretted  hydrogen.  [When  digested  near  the  boiling 
point  for  many  hours,  with  addition  of  sulphuretted  hydrogen  if  needful, 
it  is  permanent  in  air,  and  may  be  washed  with  hot  water  without  dan- 
ger of  oxidation.]  Sulphide  of  copper  dissolves  readily  in  boiling  nitric 
acid,  with  separation  of  sulphur.  Hydrochloric  acid  dissolves  it  with 
difficulty.  This  is  the  reason  why  sulphuretted  hydrogen  precipitates  cop- 
per entirely  from  solutions  which  contain  even  a very  large  amount  of  free 
hydrochloric  acid  (Grundmann  J).  Only  when  we  dissolve  a copper  salt 


* Arch,  der  Pharm.  139,  35. 

f In  some  experiments  that  I made  when  examining-  the  Weilbach  water 
I found  that  about  950000  parts  of  water  are  required  to  dissolve  1 part  of 
Cu  S. 

X Journ.  f.  prakt.  Chem.  73,  241. 


BASES  OF  GROUP  V. 


131 


§86.1 

straight  in  pure  hydrochloric  acid  of  1*1  sp.  gr.  does  any  copper  remain 
unprecipitated  (M.  Martin  *).  It  does  not  dissolve  in  solutions  of  po- 
tassa  and  of  sulphide  of  potassium,  particularly  if  these  solutions  be 
boiling;  but  it  dissolves  perceptibly  in  sulphide  of  ammonium,  and 
readily  in  cyanide  of  potassium.  Upon  intense  ignition  in  a current 
of  hydrogen  gas  it  is  converted  into  pure  Cu2  S. 

d.  Suboxide  of  copper. — If  the  blue  solution  which  is  obtained  upon  add- 
ing to  solution  of  oxide  of  copper  tartaric  acid  and  then  solution  of  soda  in 
excess,  is  mixed  with  solution  of  grape  sugar  or  sugar  of  milk,  and  heat 
applied,  an  orange-yellow  precipitate  of  hydrated  suboxide  of  copper  is 
formed,  which  contains  the  whole  of  the  copper  originally  present  in  the 
solution,  and  after  a short  time,  more  particularly  upon  the  application 
of  a somewhat  strong  heat,  turns  red,  owing  to  the  conversion  of  the 
hydrate  into  anhydrous  suboxide  (Cu2  O).  The  precipitate,  which  is 
insoluble  in  water,  retains  a portion  of  alkali  with  considerable  tena- 
city. When  acted  upon  with  dilute  sulphuric  acid,  it  gives  sulphate 
of  copper,  which  dissolves,  and  metallic  copper,  which  separates. 

e.  Subsulphocyanide  of  copper  (Cu2,  Cy  S2),  formed  when  sulpho- 
cyanide  of  potassium  is  added  to  a solution  of  oxide  of  copper,  mixed 
with  sulphurous  or  hypophosphorous  acid,  is  a white  precipitate  insolu- 
ble in  water,  and  in  dilute  hydrochloric  or  sulphuric  acid.  On  drying 
the  salt  retains  water,  and  is,  therefore,  not  adapted  for  direct  weighing. 
When  mixed  with  sulphur  and  ignited  in  hydrogen,  it  yields  Cu2  S. 

f Subsulphide  of  copper  separates  from  hot  dilute  acid  solutions  on 
addition  of  hyposulphite  of  soda,  as  a black  precipitate  that  may  be 
washed  without  risk  of  oxidation.  When  produced  by  heating  Cu  S in 
a current  of  hydrogen  gas,  or  Cu2,  Cy  S2,  with  sulphur,  it  is  a grayish- 
black  mass,  which  may  be  ignited  and  fused,  without  suffering  decompo- 
sition, if  the  air  is  excluded. 


Cu2 63-40  79-85 

S 16-00  20-15 



, 79-40  100-00 


§ 86- 

6.  Teroxide  of  Bismuth. 

Bismuth  is  weighed  in  the  form  of  teroxide  or  as  chromate  (Bi  03, 
2 Cr  03).  Besides  these  compounds,  we  have  to  study  here  the  basic 
carbonate,  the  basic  nitrate,  and  the  tersulphide. 

a.  Teroxide  of  bismuth , prepared  by  igniting  the  carbonate  or  nitrate, 
is  a pale  lemon-yellow  powder  which,  under  the  influence  of  heat,  as- 
sumes transiently  a dark  yellow  or  reddish-brown  color.  When  heated 
to  intense  redness,  it  fuses,  without  alteration  of  weight.  Ignition 
with  charcoal,  or  in  a current  of  carbonic  oxide  gas,  reduces  it  to  the 
metallic  state.  Fusion  with  cyanide  of  potassium  also  effects  its  com- 
plete reduction  to  the  metallic  state  (H.  Bose  f).  It  is  insoluble  in 
water,  and  does  not  affect  vegetable  colors.  It  dissolves  readily  in 


* Joum.  f.  prakt.  Chem.  67,  375. 
f Ibid.  61,  188 


132 


FORMS. 


[§  86. 


those  acids  which  form  soluble  salts  with  it.  When  ignited  with 
chloride  of  ammonium  it  gives  metallic  bismuth,  the  reduction  being 
attended  with  deflagration. 


Bi 208  89*655 

03 24  10*345 


232  100*000 


b.  Carbonate  of  bismuth. — Upon  adding  carbonate  of  ammonia  in 
excess  to  a solution  of  bismuth,  free  from  hydrochloric  acid,  a white 
precipitate  of  carbonate  of  bismuth  (Bi  03,  C 02)  is  immediately  formed ; 
part  of  this  precipitate,  however,  redissolves  in  the  excess  of  the  pre- 
cipitant. But  if  the  fluid  with  the  precipitate  be  heated  before  filtra- 
tion, the  filtrate  will  be  free  from  bismuth.  (Carbonate  of  potassa  like- 
wise precipitates  solutions  of  bismuth  completely ; but  the  precipitate 
in  this  case  invariably  contains  traces  of  potassa,  which  it  is  very  diffi- 
cult to  remove  by  washing.  Carbonate  of  soda  precipitates  solutions  of 
bismuth  less  completely  than  the  carbonates  of  ammonia  and  potassa.) 
The  precipitate  obtained  by  means  of  carbonate  of  ammonia,  is  easily 
washed ; it  is  very  nearly  insoluble  in  water,  but  dissolves  readily,  with 
effervescence,  in  hydrochloric  acid  and  nitric  acid.  Upon  ignition  it 
loses  its  carbonic  acid,  leaving  teroxide  of  bismuth. 

c.  The  basic  nitrate  of  bismuth , which  is  obtained  by  mixing  with 
water  a solution  of  the  nitrate  containing  little  or  no  free  acid,  presents 
the  appearance  of  a white,  crystalline  powder.  It  cannot  be  washed 
with  pure  cold  water,  without  suffering  a decided  alteration.  It  becomes 
more  basic,  while  the  washings  show  an  acid  reaction,  and  contain  bis- 
muth. If  the  basic  salt,  however,  be  washed  with  cold  water  contain- 
ing -g"Q~Q  of  nitrate  of  ammonia,  no  bismuth  passes  through  the  filter. 
The  solution  of  nitrate  of  ammonia  must  not  be  warm.  These  remarks 
only  apply  in  the  absence  of  free  nitric  acid  (J.  Lowe*).  On  ignition 
the  basic  nitrate  passes  into  the  pure  teroxide. 

d.  Chromate  of  bismuth  (Bi  03,  2 Cr  03),  which  is  produced  by  add- 
ing bichromate  of  potassa,  slightly  in  excess,  to  a neutral  solution  of 
nitrate  of  bismuth,  is  an  orange-yellow,  dense,  readily-subsiding  precipi- 
tate, insoluble  in  water,  even  in  presence  of  some  free  chromic  acid,  but 
soluble  in  hydrochloric  acid  and  nitric  acid.  It  may  be  dried  at  from 
100°  to  112°,  without  suffering  decomposition  (Lowe  f). 

Bi  03  232*00  69*78 

2 Cr  03 100*48  30*22 


332*48  100*00 

e.  Tersulphide  of  bismuth , prepared  in  the  wet  way,  is  a brownish- 
black,  or  black  precipitate,  insoluble  in  water,  dilute  acids,  alkalies,  al- 
kaline sulphides,  sulphite  of  soda,  and  cyanide  of  potassium.  In  mod- 
erately concentrated  nitric  acid  it  dissolves,  especially  on  warming,  to 
nitrate,  with  separation  of  sulphur.  Hence  in  precipitating  bismuth 
from  a nitric  acid  solution,  care  should  be  taken  to  dilute  sufficiently. 
Hydrochloric  acid  impedes  the  precipitation  of  bismuth  by  sulphuretted 
hydrogen  only  when  a very  large  excess  is  present,  and  the  fluid  is  quite 


Joum.  f.  prakt.  Chem.  74,  341. 


f Ibid.  67,  291. 


§87.] 


BASES  OF  GROUP  V. 


133 


concentrated.  The  sulphide  does  not  change  in  the  air.  Dried  at  100°, 
it  continually  takes  up  oxygen  and  increases  slightly  in  weight ; if  the 
drying  is  protracted  this  increase  may  be  considerable  (Expt.  No.  58). 
Fused  with  cyanide  of  potassium,  it  is  completely  reduced  (H.  Rose). 
Reduction  takes  place  more  slowly  by  ignition  in  a current  of  hydrogen. 


Bi 208  81-25 

S3  48  18-75 


256  100-00 


§ 87. 

7.  Oxide  of  Cadmium. 

Cadmium  is  weighed  either  as  oxide  or  as  sulphide.  Besides  these 
substances,  we  have  to  examine  carbonate  of  cadmium. 

a.  Oxide  of  cadmium , produced  by  igniting  the  carbonate  or  nitrate 
of  cadmium,  is  a powder,  the  color  of  which  varies  from  yellowish  brown 
to  reddish  brown.  The  application  of  a white  heat  fails  to  fuse,  volati- 
lize, or  decompose  it ; it  is  insoluble  in  water,  but  dissolves  readily  in 
acids ; it  does  not  alter  vegetable  colors.  Ignition  with  charcoal,  or  in 
a current  of  hydrogen,  carbonic  oxide,  or  carburetted  hydrogen,  reduces 
it  readily,  the  metallic  cadmium  escaping  in  the  form  of  vapor. 


Cd 56-00  87-50 

O 8-00  12-50 


64-00  100-00 

b.  Carbonate  of  cadmium  is  a white  precipitate,  insoluble  in  water 
and  in  the  fixed  alkaline  carbonates,  and  extremely  sparingly  soluble  in 
carbonate  of  ammonia.  It  loses  its  water  completely  upon  desiccation. 
Ignition  converts  it  into  oxide. 

c.  Sulphide  of  cadmium , produced  in  the  wet  way,  is  a lemon-yellow 
to  orange-yellow  precipitate,  insoluble  in  water,  dilute  acids,  alkalies, 
alkaline  sulphides,  sulphite  of  soda,  and  cyanide  of  potassium  (Expt. 
No.  59).  It  dissolves  readily  in  concentrated  hydrochloric  acid,  with 
evolution  of  sulphuretted  hydrogen.  In  precipitating,  therefore,  with 
sulphuretted  hydrogen,  a cadmium  solution  should  not  contain  too 
much  hydrochloric  acid,  and  should  be  sufficiently  diluted.  The  sulphide 
dissolves  in  moderately  concentrated  nitric  acid,  with  separation  of  sul- 
phur. It  may  be  washed,  and  dried  at  100°  or  105°,  without  under- 
going decomposition.  Even  on  gently  igniting  the  sulphide  of  cadmium 
in  a current  of  hydrogen,  it  volatilizes  in  appreciable  amount  (H.  Rose*), 
partially  unchanged,  partially  as  metallic  vapor. 


Cd 56-00  77-78 

S 16-00  22-22 


72-00  100-00 


Pogg.  Anna!.  110,  134. 


134 


FORMS. 


METALLIC  OXIDES  OF  THE  SIXTH  GROUP. 

§88. 

1.  Teroxide  of  Gold. 

Gold  is  always  weighed  in  the  metallic  state.  Besides  metallic  gold, 
we  have  to  consider  the  tersulphide. 

a.  Metallic  gold , obtained  by  precipitation,  presents  the  appearance  of 
a blackish-brown  powder,  destitute  of  metallic  lustre,  which  it  assumes, 
however,  upon  pressure  or  friction  ; when  coherent  in  a compact  mass, 
it  exhibits  the  well-known  bright  yellow  color  peculiar  to  it.  It  fuses 
only  at  a white  heat,  and  resists,  accordingly,  all  attempts  at  fusion  over 
a spirit-lamp.  It  remains  wholly  unaltered  in  the  air  and  at  a red  heat, 
and  is  not  in  the  slightest  degree  affected  by  water,  nor  by  any  simple 
acid.  Nitrohydrochloric  acid  dissolves  it  to  terchloride. 

b.  Tersulphide  of  gold. — When  sulphuretted  hydrogen  is  transmitted 
through  a cold  dilute  solution  of  terchloride  of  gold,  the  whole  of  the 
gold  separates  as  tersulphide  (Au  S3),  in  form  of  a brownish-black  pre- 
cipitate. If  this  precipitate  is  left  in  the  fluid,  it  is  gradually  transformed 
into  metallic  gold  and  free  sulphuric  acid.  Upon  transmitting  sulphuret- 
ted hydrogen  through  a warm  solution  of  terchloride  of  gold,  a protosul- 
phide ( Au  S)  precipitates,  with  simultaneous  formation  of  sulphuric  and 
hydrochloric  acids. 

(2  Au  Cl, +3  H S-j-3  H 0=2  Au  S+6  H Cl+S  03.) 

The  tersulphide  is  insoluble  in  water,  hydrochloric  acid,  and  nitric 
acid,  but  dissolves  in  nitrohydrochloric  acid.  The  colorless  sulphide  of 
ammonium  fails  to  dissolve  it ; but  it  dissolves  almost  entirely  in  the 
yellow  sulphide  of  ammonium,  and  completely  upon  addition  of  potassa. 
It  dissolves  in  potassa,  with  separation  of  gold.  Yellow  sulphide  of 
potassium  dissolves  it  completely.  Exposure  to  a moderate  heat  reduces 
it  to  the  metallic  state. 

§ 89. 

2.  Binoxide  of  Platinum. 

Platinum  is  invariably  weighed  in  the  metallic  state  ; it  is  generally 
precipitated  as  bichloride  of  platinum  and  chloride  of  ammonium, 

or  as  BICHLORIDE  OF  PLATINUM  AND  CHLORIDE  OF  POTASSIUM,  rarely  as 
BISULPHIDE  of  platinum. 

a.  Metallic  platinum , produced  by  igniting  the  bichloride  of  platinum 
and  chloride  of  ammonium,  or  the  bichloride  of  platinum  and  chloride 
of  potassium,  presents  the  appearance  of  a gray,  lustreless,  porous  mass 
(spongy  platinum).  The  fusion  of  platinum  can  be  effected  only  at  the 
very  highest  degrees  of  heat.  It  remains  wholly  unaltered  in  the  air, 
and  even  the  most  intense  heat  of  our  furnaces  fails  to  affect  it.  It  is 
not  attacked  by  water,  or  simple  acids,  and  scarcely  by  aqueous  solutions 
of  the  alkalies.  Nitrohydrochloric  acid  dissolves  it  to  bichloride. 

b.  The  properties  of  bichloride  of  platinum  and  chloride  of  potassium, 
and  those  of  bichloride  of  platinum  and  chloride  of  ammonium , have  been 
given  already  in  §§  68  and  70  respectively. 

c.  Bisulphide  of  platinum. — When  a concentrated  solution  of  bichlo- 


§90.] 


METALLIC  OXIDES  OF  GROUP  VI. 


135 


ride  of  platinum  is  mixed  with  sulphuretted  hydrogen  water,  or  when 
sulphuretted  hydrogen  gas  is  transmitted  through  a rather  dilute  solu- 
tion of  the  bichloride,  no  precipitate  forms  at  first ; after  standing  some 
time,  however,  the  solution  turns  brown,  and  finally  a precipitate  sub- 
sides. But  if  the  mixture  of  solution  of  bichloride  of  platinum  with 
sulphuretted  hydrogen  in  excess,  is  gradually  heated  (finally  to  ebulli- 
tion), the  whole  of  the  platinum  separates  as  bisulphide  (free  from  any 
admixture  of  bichloride).  The  bisulphide  of  platinum  is  insoluble  in 
water  and  in  simple  acids ; but  it  dissolves  in  nitrohydrochloric  acid. 
It  dissolves  partly  in  caustic  alkalies,  with  separation  of  platinum,  and 
completely  in  alkaline  sulphides.  When  sulphuretted  hydrogen  is  trans- 
mitted through  water  holding  minutely  divided  bisulphide  of  platinum 
in  suspension,  the  bisulphide,  absorbing  sulphuretted  hydrogen,  acquires 
a light  gravish-brown  color  ; the  sulphuretted  hydrogen  thus  absorbed, 
separates  again  upon  exposure  to  the  air.  When  moist  bisulphide  of 
platinum  is  exposed  to  the  air,  it  is  gradually  decomposed,  being  con- 
verted into  metallic  platinum  and  sulphuric  acid.  Ignition  in  the  aii 
reduces  bisulphide  of  platinum  to  the  metallic  state. 

§ 90. 

' 

3.  Teroxide  of  Antimony. 

Antimony  is  weighed  as  tersulphide,  as  antimonious  acid,  or  more 
rarely  in  the  metallic  state. 

a.  Upon  transmitting  sulphuretted  hydrogen  through  a solution  of 
terchloride  of  antimony  mixed  with  tartaric  acid,  an  orange-red  pre- 
cipitate of  amorphous  tersulphide  is  obtained,  mixed  at  first  with  a small 
portion  of  basic  terchloride  of  antimony.  However,  if  the  fluid  is  thor- 
oughly saturated  with  sulphuretted  hydrogen,  and  a gentle  heat  applied, 
the  terchloride  mixed  with  the  precipitate  is  decomposed,  and  the  pure 
tersulphide  of  antimony  obtained.  Tersulphide  of  antimony  is  insoluble 
in  water  and  dilute  acids  ; it  dissolves  in  concentrated  hydrochloric  acid, 
with  evolution  of  sulphuretted  hydrogen.  In  precipitating  with  sul- 
phuretted hydrogen,  therefore,  antimony  solutions  should  not  contain 
too  much  free  hydrochloric  acid,  and  should  be  sufficiently  diluted.  The 
amorphous  tersulphide  dissolves  readily  in  potassa,  sulphide  of  ammo- 
nium, and  sulphide  of  potassium,  sparingly  in  ammonia,  very  slightly  in 
carbonate  of  ammonia,  and  not  at  all  in  bisulphite  of  potassa.  The  amor- 
phous sulphide,  dried  in  the  desiccator  at  the  ordinary  temperature, 
loses  very  little  weight  at  100°  ; if  kept  longer  at  this  latter  temperature, 
its  weight  remains  constant.  But  it  still  retains  a little  water,  which 
does  not  perfectly  escape  even  at  190°,  but /at  200°  the  sulphide  becomes 
anhydrous,  turning  black  and  crystalline  (H.  Bose*  and  Expt.  No.  60). 
Ignited  gently  in  a stream  of  carbonic  acid,  the  weight  of  this  anhydrous 
sulphide  remains  constant ; in  a very  intense  heat,  a small  amount  vola- 
tilizes. The  amorphous  sulphide,  if  long  exposed  to  the  action  of  air, 
in  presence  of  water,  slowly  takes  up  oxygen,  so  that  on  treatment  with 
tartaric  acid  it  yields  a filtrate  containing  teroxide. 

The  sulphides  corresponding  to  the  antimonious  and  antimonic  acids 
are  equally  insoluble  in  water,  also  in  water  containing  sulphuretted 
hydrogen.  The  pure  pentasulphide  dissolves  completely  in  ammonia, 


* Joum.  f.  prakt.  Chem.  59,  331. 


136 


FORMS. 


[§91 

especially  on  warming;  traces  only  dissolve  in  carbonate  of  ammonia. 
On  heating  the  dried  pentasulphide  in  a current  of  carbonic  acid  2 eq. 
of  sulphur  escape,  black  crystalline  tersulphide  remaining. 

On  treating  the  ter-  or  penta-sulphide  with  fuming  nitric  acid  violent 
oxidation  sets  in.  We  obtain  first  antimonic  acid  and  pulverulent  sepa- 
rated sulphur ; on  evaporating  to  dryness,  antimonic  acid  and  sulphuric 
acid ; and  lastly,  on  igniting,  antimonious  acid.  The  same  (antimonious 
acid)  is  obtained  by  igniting  the  sulphide  with  30  to  50  times  its 
amount  of  oxide  of  mercury  (Bunsen  *).  Ignition  in  a current  of  hy- 
drogen converts  the  sulphides  of  antimony  into  the  metallic  state. 


Sb 122-00  71-77 

*S3 48-00  28-23 


170-00  100-00 

b.  Antimonious  acid  is  a white  powder,  which,  when  heated,  acquires 
transiently  a yellow  tint ; it  is  infusible  ; it  is  fixed,  provided  reducing 
gases  be  excluded.  It  is  almost  insoluble  in  water,  and  dissolves  in 
hydrochloric  acid  with  very  great  difficulty.  It  undergoes  no  alteration 
on  treatment  with  sulphide  of  ammonium.  It  manifests  an  acid  reac- 
tion when  placed  upon  moist  litmus  paper. 


Sb 122-0  79-22 

04  32-0  20-78 


154-0  100-00 

c.  Metallic  antimony , produced  in  the  wet  way,  by  precipitation,  pre- 
sents the  appearance  of  a lustreless  black  powder.  It  may  be  dried  at 
100°  without  suffering  any  alteration.  It  fuses  at  a moderate  red  heat. 
Upon  ignition  in  a current  of  gas,  e.g.  hydrogen,  it  volatilizes,  without 
formation  of  antimonetted  hydrogen.  Hydrochloric  acid  has  very  little 
action  on  it,  even  when  concentrated  and  upon  ebullition.  Nitric  acid 
converts  it  into  teroxide  of  antimony,  mixed  with  more  or  less  antimo- 
nious acid,  according  to  the  concentration  of  the  nitric  acid. 

§ 91. 

4.  Protoxide  of  Tin;  and  5.  Binoxide  of  Tin. 

Tin  is  generally  weighed  in  the  form  of  binoxide  ; besides  the  binox- 
ide, we  have  to  examine  protosulphide  and  bisulphide  of  tin. 

a.  Binoxide  of  tin. — The  hydrate  of  the  binoxide  b ( hydrated  meta- 
stannic  acid)  is  obtained  in  the  form  of  a white  precipitate,  by  the  action 
of  nitric  acid  upon  metallic  tin,  or  by  evaporating  a solution  of  tin  with 
nitric  acid  in  excess.  This  precipitate  is  insoluble  in  water,  nitric  acid, 
and  sulphuric  acid,  and  dissolves  but  sparingly  in  hydrochloric  acid.  It 
reddens  litmus,  even  when  thoroughly  washed.  But  if  we  precipitate 
solution  of  bichloride  of  tin  with  an  alkali,  or  with  sulphate  of  soda,  or 
nitrate  of  ammonia,  we  obtain  the  hydrate  of  the  binoxide  a,  which  dis- 
solves readily  in  hydrochloric  acid.  Upon  intense  ignition,  both  hy- 
drates are  converted  into  the  anhydrous  binoxide  of  tin.  Mere  heating 
to  redness  is  not  sufficient  to  expel  all  the  water  (Dumas  f). 


* Annal.  d.  Chem.  u.  Pharm.  106,  3. 
f Ibid.  105,  104. 


92.] 


METALLIC  OXIDES  OF  GROUP  VI. 


137 


Binoxide  of  tin  is  a straw-colored  powder,  which,  under  the  influence 
of  heat,  transiently  assumes  a different  tint,  varying  from  bright  yellow 
to  brown.  It  is  insoluble  in  water  and  acids,  and  does  not  alter  the 
color  of  litmus  paper.  Mixed  with  chloride  of  ammonium  in  excess, 
and  ignited,  it  volatilizes  completely  as  bichloride.  If  binoxide  of  tin  is 
fused  with  cyanide  of  potassium,  all  the  tin  is  obtained  in  form  of  metal- 
lic globules,  which  may  be  completely,  and  without  the  least  loss  of 
metal,  freed  from  the  adhering  slag,  by  extracting  with  dilute  spirit  of 
wine  and  rapidly  decanting  the  fluid  from  the  tin  globules  (H.  Bose  *). 


Sn 59  78*67 

02 16  # 21*33 


75  100*00 

b.  Hydrated  protosulphide  of  tin  forms  a brown  precipitate,  insoluble 
in  water,  sulphuretted  hydrogen  water,  and  dilute  acids.  In  precipita- 
ting tin  from  solutions  of  the  protoxide  by  means  of  sulphuretted  hy- 
drogen, free  hydrochloric  acid  must  not  be  present  in  too  large  amount, 
and  the  solution  must  be  diluted  sufficiently.  Ammonia  fails  to  dissolve 
it ; but  it  dissolves  pretty  readily  (as  bisulphide)  in  the  yellow  sulphide 
of  ammonium,  and  in  the  yellow  sulphide  of  potassium;  it  dissolves 
readily  in  hot  concentrated  hydrochloric  acid.  Heated,  with  exclusion 
of  air,  it  loses  its  water  of  hydration,  and  is  converted  into  anhydrous 
protosulphide  of  tin ; when  exposed  to  the  continued  action  of  a gentle 
heat,  with  free  access  of  air,  it  is  converted  into  sulphurous  acid,  which 
escapes,  and  binoxide  of  tin,  which  remains. 

c.  Hydrated  bisulphide  of  tin  forms  a light-yellow  precipitate.  In 
washing  with  pure  water,  it  is  inclined  to  yield  a turbid  filtrate  and  to 
stop  up  the  pores  of  the  filter ; this  annoyance  is  got  over  by  washing 
with  water  containing  chloride  of  sodium,  acetate  of  ammonia,  or  the 
like  (Bunsen).  On  drying,  the  precipitate  assumes  a darker  tint.  It 
is  insoluble  in  water ; it  dissolves  with  difficulty  in  ammonia,  but  read- 
ily in  potassa,  alkaline  sulphides,  and  hot  concentrated  hydrochloric 
acid.  It  is  insoluble  in  bisulphite  of  potassa.  In  precipitating  tin  from 
solutions  of  the  binoxide  by  sulphuretted  hydrogen,  the  solution  should 
not  contain  too  much  free  hydrochloric  acid,  and  should  be  sufficiently 
diluted.  When  heated,  with  exclusion  of  air,  it  loses  its  water  of  hy- 
dration, and,  at  the  same  time,  according  to  the  greater  or  less  degree  of 
heat  applied,  one-half,  or  a whole  equivalent  of  sulphur,  becoming  con- 
verted either  into  sesquisulphide,  or  into  protosulphide  of  tin;  when 
heated  very  slowly,  with  free  access  of  air,  it  is  converted  into  binoxide 
of  tin,  with  disengagement  of  sulphurous  acid. 

§ 92. 

6.  Arsenious  Acid  ; and  7.  Arsenic  Acid. 

Arsenic  is  weighed  either  as  arseniate  of  lead,  as  tersulphide,  as 

ARSENIATE  OF  MAGNESIA  AND  AMMONIA,  Or  as  BASIC  ARSENIATE  OF  SESQUI- 
oxide  of  iron  ; besides  these  forms,  we  have  here  to  examine  also  ar- 
SENIO-MOLYBDATE  OF  AMMONIA. 

a.  Arseniate  of  lead , in  the  pure  state,  is  a white  powder,  which  agglu- 


* Joum.  f.  prakt.  Chem.  61,  189. 


138 


FORMS. 


[§  92. 

tinates  when  exposed  to  a gentle  red  heat,  at  the  same  time  transitorily 
acquiring  a yellow  tint ; it  fuses  when  exposed  to  a higher  degree  of  heat. 
When  strongly  ignited,  it  suffers  a slight  diminution  of  weight,  losing  a 
small  proportion  of  arsenic  acid,  which  escapes  as  arsenious  acid  and 
oxygen.  In  analysis  we  have  never  occasion  to  operate  upon  the  pure 
arseniate  of  lead,  but  upon  a mixture  of  it  with  free  oxide  of  lead. 

b.  Tersulphide  of  arsenic  forms  a precipitate  of  a rich  yellow  color ; it 
is  insoluble  in  water,*  and  also  in  sulphuretted  hydrogen  water.  When 
boiled  with  water,  or  left  for  several  days  in  contact  with  chat  fluid,  it 
undergoes  a very  trifling  decomposition : a trace  of  arsenious  acid  dis- 
solves in  the  water,  and  a minute  proportion  of  sulphuretted  hydrogen  is 
disengaged.  This  does  not  in  the  least  interfere,  however,  with  the 
washing  of  the  precipitate.  The  precipitate  may  be  dried  at  100°,  with- 
out suffering  decomposition  ; the  whole  of  the  water  which  it  contains  is 
expelled  at  that  temperature.  When  exposed  to  a stronger  heat,  tersul- 
phide of  arsenic  transitorily  assumes  a brownish-red  color,  fuses,  and 
finally  rises  in  vapor,  without  suffering  decomposition.  It  dissolves 
readily  in  alkalies,  alkaline  carbonates,  alkaline  sulphides,  bisulphite  of 
potassa,  and  nitrohydrochloric  acid  ; but  it  is  scarcely  soluble  in  boiling 
concentrated  hydrochloric  acid.  Red  fuming  nitric  acid  converts  it  into 
arsenic  acid  and  sulphuric  acid. 


As 75  60-98 

S3  48  39-02 


123  100-00 

c.  Arseniate  of  magnesia  and  ammonia  forms  a white,  somewhat  trans- 
parent, finely  crystalline  precipitate,  which  has  the  formula  2 Mg  O,  N H4 
O,  As  05  4-  12  aq. 

At  100°,  it  loses  11  eq.  water  ; the  formula  of  the  precipitate  dried  at 
that  temperature  is  accordingly  2 Mg  O,  N H4  O,  As  05  + aq.  Upon 
ignition  it  loses  its  water  and  ammonia,  and  changes  to  2 Mg  O,  As  Os. 
But  as  the  ammoniacal  gas  exercises  a reducing  action  upon  the  arsenic 
acid,  the  new  compound  suffers  a loss  of  weight,  which  is  the  more  con- 
siderable the  longer  the  ignition  is  continued  ; it  amounts  to  from  4 — 12 
per  cent,  of  the  arsenic  originally  present  in  the  salt  (H.  Rose).  Arseniate 
of  magnesia  and  ammonia  dissolves  very  sparingly  in  water,  one  part  of 
the  salt  dried  at  100°,  requiring  2656,  one  part  of  the  anhydrous  salt, 
2788  parts  of  water  of  15°.  It  is  still  more  sparingly  soluble  in  ammo- 
niated  water,  one  part  of  the  salt  dried  at  100°  requiring  15038,  one  part 
of  the  anhydrous  salt,  15786  parts  of  a mixture  of  one  part  of  solution  of 
ammonia  (0*96  sp.  gr.),  and  3 parts  of  water  at  15°.  In  water  contain- 
ing chloride  of  ammonium,  it  is  much  more  readily  soluble,  one  part  of  the 
anhydrous  salt  requiring  886  parts  of  a solution  of  one  part  of  chloride  of 
ammonium  in  7 parts  of  water.  Presence  of  ammonia  diminishes  the 
solvent  capacity  of  the  chloride  of  ammonium  solution  : one  part  of  the 
anhydrous  salt  requires  3014  parts  of  a mixture  of  60  parts  of  water,  10  of 
solution  of  ammonia  (0*96  sp.  gr.)  and  one  of  chloride  of  ammonium,  t 

* In  some  experiments  which  I had  occasion  to  make,  in  the  course  of  an  analy- 
sis of  the  springs  of  Wielbach  (Chemische  Untersuchung  der  wichtigsten  JYLaeral- 
wasser  des  Herzogthums  Nassau  von  Dr.  Fresenius,  Y.  Schwefelquelle  zu  Weil- 
bach.  Wiesbaden,  Kreidel  und  Niedner.  1856),  I found  that  one  part  of  As  S» 
dissolves  in  about  1 million  parts  of  water. 

f Zeitschrift  f.  anal.  Chem.  3,  206. 


§ 93.]  ACIDS  OF  GROUP  1.  139 

COMPOSITION  OF  THE  ARSENIATE  OF  MAGNESIA  AND  AMMONIA 
DRIED  AT  100°. 

2 Mg  O 40  21*05 

N H4  O 26  13-68 

As  Os  115  60-53 

HO  9 4-74 


190  100-00 

d.  Arseniate  of  sesquioxide  of  iron. — The  white  slimy  precipitate,  pro- 
duced by  the  action  of  ordinary  arseniate  of  soda  upon  solution  of  sesqui- 
chloride  of  iron,  has  the  composition  2 Fe2  03,  3 HO,  3 As  05  -f-  9 aq. 
It  dissolves  in  solution  of  ammonia,  imparting  a yellow  color  to  the  fluid. 

Besides  this  compound,  there  exist  still  several  others,  with  larger  pro- 
portions of  sesquioxide  of  iron  ; thus  we  have  Fe2  03,  As  06,  which  falls 
down  -f-  5 aq.  upon  the  precipitation  of  arsenic  acid  with  acetate  of  ses- 
quioxide of  iron  (Kotschoubey)  ; 2 Fe2  03,  As  05,  which  is  obtained  4- 
12  aq.,  when  basic  arseniate  of  protoxide  of  iron  is  oxidized  with  nitric 
acid,  and  ammonia  added  ; — 16  Fe2  03,  As  05,  which  forms  + 24  aq., 
upon  boiling  the  less  basic  compounds  with  solution  of  potassa  in  excess  ; 
(Berzelius).  The  two  latter  compounds  are  not  soluble  in  ammonia ; the 
last  is  quite  like  hydrated  sesquioxide  of  iron.  [Doubtless  the  basic 
arseniate  of  sesquioxide  of  iron,  like  the  analogous  phosphate,  loses  acid 
as  long  as  it  is  washed,  and  therefore  the  precipitate  has  no  definite  com- 
position. ] In  Berthier’s  method  of  estimating  arsenic  acid,  we  obtain  mix- 
tures of  these  different  salts.  They  are  the  better  adapted  for  the  purpose, 
the  more  basic  they  are  ; being  the  more  insoluble  in  ammonia,  and  at  the 
same  time  more  easily  washed.  Upon  ignition  the  water  alone  is  expelled, 
provided  the  heat  be  very  gradually  increased.  But  if  the  salt  is  suddenly 
exposed  to  a strong  heat,  before  the  adhering  ammonia  has  escaped,  part 
of  the  arsenic  acid  is  thereby  reduced  to  arsenious  acid  (H.  Bose). 

e.  Arsenio-molybdate  of  ammonia. — If  a fluid  containing  arsenic  acid 
is  mixed  with  a large  proportion  of  molybdate  of  ammonia,  and  sufficient 
nitric  or  hydrochloric  acid  to  redissolve  the  precipitate  of  molybdic  acid 
which  forms  at  first,  and  the  fluid  heated  to  boiling,  a yellow  precipitate  of 
arsenio-molybdate  of  ammonia  separates— provided  the  molybdic  acid  be 
present  in  excess.  This  precipitate  comports  itself  with  solvents  like  the 
analogous  compound  of  phosphoric  acid  ; it  is,  like  the  latter,  insoluble  in 
water,  salts,  and  free  acids,  particularly  nitric  acid,  provided  an  excess  of 
solution  of  molybdate  of  ammonia,  mixed  with  acid  in  moderate  excess, 
be  present.  Seligsohn  * found  it  to  be  composed  of  87*666  per  cent,  of 
molybdic  acid,  6*308  arsenic  acid,  4*258  ammonia,  and  1*768  water. 

JB. — Forms  in  which  the  acids  are  weighed  or  precipitated. 

ACIDS  OF  THE  FIRST  GROUP. 

§93. 

1.  Arsenious  Acid  and  Arsenic  Acid. — See  § 92. 

2.  Chromic  Acid. 

Chromic  acid  is  weighed  either  in  the  form  of  sesquioxide,  or  in  that 
of  CHROMATE  OF  LEAD. 


* Joum.  f.  prakt.  Chem.  67,  481. 


140 


FORMS. 


[§  93. 


a.  Sesquioxide  of  chromium. — See  § 76. 

h.  Chromate  of  lead  obtained  by  precipitation  forms  a bright  yellow 
precipitate,  insoluble  in  water  and  acetic  acid,  barely  soluble  in  dilute 
nitric  acid,  readily  in  solution  of  potassa.  When  chromate  of  lead  is 
boiled  with  concentrated  hydrochloric  acid,  it  is  readily  decomposed, 
chloride  of  lead  and  sesquichloride  of  chromium  being  formed.  Addition 
of  alcohol  tends  to  promote  this  decomposition.  Chromate  of  lead  is 
unalterable  in  the  air  ; it  dries  thoroughly  at  100°.  Under  the  influence 
of  heat  it  transitorily  acquires  a reddish-brown  tint ; it  fuses  at  a red 
heat ; when  heated  beyond  its  point  of  fusion,  it  loses  oxygen,  and  is 
transformed  into  a mixture  of  sesquioxide  of  chromium  and  basic  chro- 
mate of  lead.  Heated  in  contact  with  organic  substances,  it  readily 
yields  oxygen  to  the  latter. 


Pb  O 111-50  68-94 

Cr  03  50-24  31*06 


161-74  100-00 

3.  Sulphuric  Acid. 

Sulphuric  acid  is  determined  best  in  the  form  of  sulphate  of  baryta, 
for  the  properties  of  which  see  § 71. 

4.  Phosphoric  Acid. 

The  principal  forms  into  which  phosphoric  acid  is  converted  are  as  fol- 
lows : PHOSPHATE  OF  LEAD,  PYROPHOSPHATE  OF  MAGNESIA,  BASIC  PHOS- 

PHATE OF  MAGNESIA  (3  Mg  O,  P 05),  BASIC  PHOSPHATE  OF  SESQUIOXIDE 
OF  IRON,  PHOSPHATE  OF  SESQUIOXIDE  OF  URANIUM,  PHOSPHATE  OF  BINOX- 

ide  of  tin,  and  phosphate  of  silver.  Besides  these  compounds,  we 
have  to  examine  phosphate  of  suboxide  of  mercury,  and  phospho- 

MOLYBDATE  OF  AMMONIA. 

a.  The  phosphate  of  lead  obtained  in  the  course  of  analysis  is  rarely 
quite  pure,  but  is  generally  mixed  with  free  oxide  of  lead.  In  this  mix- 
ture we  have  accordingly  the  basic  phosphate  of  lead  (3  Pb  O,  P 06)  ; in 
the  pure  state,  this  presents  the  appearance  of  a white  powder ; it  is  in- 
soluble in  water  and  in  acetic  acid,  and  equally  so  in  ammonia  ; it  dis- 
solves readily  in  nitric  acid.  When  exposed  to  the  action  of  heat,  it 
fuses,  without  undergoing  decomposition. 

b.  Pyrophosphate  of  magnesia. — See  § 74. 

c.  Pasic  phosphate  of  magnesia  (3  Mg  O,  P 05). — This  compound  is 
produced  by  mixing  a solution  of  an  alkaline  phosphate,  containing 
chloride  of  ammonium,  with  magnesia,  evaporating  the  mixture,  heating 
the  residue  until  the  chloride  of  ammonium  is  completely  expelled,  and 
finally  treating  with  water ; the  compound  so  produced  contains  an  ex- 
cess of  magnesia.  It  is  sufficient  for  our  purpose  to  state  that  it  is  near- 
ly absolutely  insoluble  in  water  and  in  solutions  of  salts  of  the  alkalies 
(F.  B.  Schulze  *). 

d.  Basic  phosphate  of  sesquioxide  of  iron. 

If  a solution  of  phosphoric  acid  or  of  phosphate  of  lime  in  acetic  acid 
is  carefully  precipitated  with  a solution  of  acetate  of  sesquioxide  of  iron, 
or  with  a mixture  of  iron-alum  and  acetate  of  soda,  so  that  the  iron  salt 


* Joum.  f.  prakt.  Chem.  63,  440. 


93-1 


ACIDS  OF  GROUP  I. 


141 


may  just  predominate,  the  precipitate  always  contains  1 eq.  P 05  to  1 eq. 
Fe2  03  (Fawsky,  Wittstein,  E.  Davy  *) ; if,  on  the  other  hand,  the 
acetate  of  iron  is  in  larger  excess,  the  precipitate  contains  more  base. 
Wittstein  obtained,  by  using  considerable  excess  of  acetate  of  iron,  a 
precipitate  of  the  formula  4 Fe2  03,  3 P 05.  Precipitates,  obtained  with 
a small  excess  of  the  precipitant,  possess  a composition  varying  between 
the  above-mentioned  limits.  Fammelsberg  obtained  Fe2  03,  P 05  ( + 
4 aq.),  and  Wittstein  subsequently,  the  same  compound  (with  8 aq.  in- 
stead of  4),  upon  mixing  sulphate  of  sesquioxide  of  iron  with  phosphate 
of  soda  in  excess ; with  an  insufficient  quantity  of  the  phosphate  of  soda, 
the  latter  chemist  obtained  a more  yellowish  precipitate,  which  had 
the  formula 

3 (Fe203,  P 05+8  aq.)  + (FeA,  3 El  O). 

If  an  acid  fluid  containing  a considerable  excess  of  phosphoric  acid 
is  mixed  with  a small  quantity  of  solution  of  sesquioxide  of  iron,  and 
an  alkaline  acetate  added,  a precipitate  of  the  formula,  Fe203,  P 05 
+ water,  is  invariably  obtained,  which,  accordingly,  leaves  upon  ignition 
Fe2  03,  P 05  (Wittstein).  Fresh  experiments  that  I have  made  upon 
this  subject  have  positively  convinced  me  of  the  perfect  correctness  of 
this  statement  of  Wittstein’s.| 

composition. 

P 05  71  47-02 

Fe263  80  52-98 


151  100-00 

[The  discrepancies  among  the  statements  made  by  different  chemists 
as  to  the  composition  of  basic  phosphate  of  sesquioxide  of  iron  obtained 
in  the  modes  above  indicated  are  explained  by  the  observations  of  Mohr, 
that  the  precipitate  loses  phosphoric  acid  as  long  as  it  is  washed,  and  has 
consequently  no  definite  composition.] 

If  we  dissolve  phosphate  of  sesquioxide  of  iron  in  hydrochloric  acid, 
supersaturate  the  solution  with  ammonia.,  and  apply  heat,  we  obtain  more 
basic  salts,  viz.,  3 Fe2  03,  2 P A (Fammelsberg)  ; 2 Fe2  03,  P 05  (Witt- 
stein— after  long  washing).  In  Wittstein’s  experiment,  the  wash-water 
contained  phosphoric  acid.  The  white  phosphate  of  sesquioxide  of  iron 
does  not  dissolve  in  acetic  acid,  but  it  dissolves  in  a solution  of  acetatt 
of  sesquioxide  of  iron. 

Upon  boiling  the  latter  solution  (of  phosphate  of  sesquioxide  of  iro* 
in  acetate  of  sesquioxide  of  iron),  the  whole  of  the  phosphoric  acid  precipi 
tates,  together  with  the  basic  acetate  of  sesquioxide  of  iron,  as  hyperbasii 
phosphate  of  sesquioxide  of  iron  (15  Fe2G3,  P05 — (Fammelsberg).  Simi- 
lar extremely  basic  combinations  are  invariably  obtained  (often  mixed 
with  free  hydrated  sesquioxide  of  iron),  upon  precipitating  with  ammo- 
nia or  carbonate  of  baryta  a solution  containing  phosphoric  acid  and  an 
excess  of  sesquioxide  of  iron.  The  precipitate  obtained  by  carbonate  of 

* Phil.  Mag.,  xix.  p.  181.  Joum.  f.  prakt.  Chem.  80,  380. 

f In  an  experiment  made  at  a former  period  by  Will  and  myself  (Anna!,  der 
Chem.  u.  Pharm.  50,  379),  we  obtained  in  this  way  a precipitate  of  the  formula 
2 Fe2  03,  3 P 05+3  HO  + 10  aq.  ; but  I have  never  since  succeeded  in  produ 
cing  a precipitate  of  the  same  composition. 


142 


FORMS. 


baryta,  can  be  conveniently  filtered  off  and  washed,  the  filtrate  is  perfectly 
free  from  either  iron  or  phosphoric  acid  ; on  the  contrary,  the  precipitate 
obtained  by  ammonia,  especially  if  the  latter  were  much  in  excess,  is  slimy, 
and  therefore  difficult  to  wash,  and  the  filtrate  always  contains  small 
traces  of  both  iron  and  phosphoric  acid. 

e.  Phosphate  of  sesquioxide  of  uranium. — If  the  hot  aqueous  solution 
of  a phosphate  soluble  in  water  or  acetic  acid  is  mixed,  in  presence  of 
free  acetic  acid,  with  acetate  of  sesquioxide  of  uranium,  a precipitate 
of  phosphate  of  sesquioxide  of  uranium  is  immediately  formed.  If  the 
fluid  contains  much  ammoniacal  salt,  the  precipitate  contains  also  am- 
monia. The  same  precipitate  forms  also  if  alumina  or  sesquioxide  of 
iron  is  present ; but  in  that  case  it  is  always  mixed  with  more  or  less 
phosphate  of  sesquioxide  of  iron  or  phosphate  of  alumina.  Presence  of 
potassa-or  soda-salts,  on  the  contrary,  or  of  salts  of  the  alkaline  earths, 
has  no  influence  on  the  composition  of  the  precipitate. 

Phosphate  of  sesquioxide  of  uranium  and  ammonia  (2  Ur2  03,  N H4  O, 
P 05  + x H O)  is  a somewhat  gelatinous,  whitish-yellow  precipitate, 
with  a tinge  of  green.  The  best  way  of  washing  it,  at  least  so  far  as  the 
principal  part  of  the  operation  is  concerned,  is  by  boiling  with  water 
and  decanting.  If,  after  having  allowed  the  fluid  in  which  the  preci- 
pitate is  suspended  to  cool  a little,  a few  drops  of  chloroform  are  added, 
and  the  mixture  is  shaken  or  boiled  up,  the  precipitate  subsides  much 
more  readily  than  without  this  addition. 

The  precipitate  is  insoluble  in  water  and  in  acetic  acid ; but  it  dissolves 
in  mineral  • acids  ; acetate  of  ammonia,  added  in  sufficient  excess,  com- 
pletely re-precipitates  it  from  this  solution,  upon  application  of  heat. 
Upon  igniting  the  precipitate,  no  matter  whether  containing  ammonia 
or  not,  phosphate  of  sesquioxide  of  uranium  of  the  formula  2 Ur2  03, 
P 05  is  produced.  This  has  the  color  of  the  yolk  of  an  egg.  If  the 
precipitate  is  ignited  in  presence  of  charcoal  or  of  some  reducing  gas, 
partial  reduction  to  phosphate  of  protoxide  of  uranium  ensues,  owing  to 
which  the  ignited  mass  acquires  a greenish  tint ; however,  upon  warm- 
ing the  greenish  residue  with  some  nitric  acid,  the  green  salt  of  the 
protoxide  is  readily  reconverted  into  the  yellow  salt  of  the  sesquioxide. 
Phosphate  of  sesquioxide  of  uranium  is  not  hygroscopic,  and  may  there- 
fore be  ignited  and  weighed  in  an  open  platinum  dish  (A.  Arendt  and 
W.  Knop  *). 


2 Ur203  285*6  80*09 

P 05 71*0  19*91 


356*6  100*00 

The  one-fifth  part  of  the  precipitate  may  accordingly  be  calculated  as 
phosphoric  acid  in  ordinary  analyses. f 
f Phosphate  of  binoxide  of  tin  is  never  obtained  in  the  pure  state  in 
the  analytical  process,  but  contains  always  an  admixture  of  hydrated 


* Chemisches  Centralblatt,  1856,  769,  803  ; and  1857,  177. 

\ The  equivalent  of  uranium  is  here  taken  as  59*4,  according  to  Ebelmen.  If 
we  take  it  according  to  Peligot,  as  60,  the  ignited  phosphate  would  contain 
80  22  Ur..  0:i.  and  19-78  phosphoric  acid.  W.  Knop  and  Arendt  found  in  four 
experiments  20  13,  20  06,  20  04,  and  20  04  respectively  (in  another  20  77).  It 
will  be  seen  that  these  numbers  agree  better  with  the  composition  as  reckoned 
from  Ebelmen’s  than  from  Peligot’s  equivalent. 


§ 93.]  ACIDS  OF  GROUP  I.  143 

metastannic  acid  in  excess,  which,  upon  ignition,  changes  to  metastannic 
acid.  It  has,  generally  speaking,  the  same  properties  as  hydrated  meta- 
stannic acid,  and  is  more  particularly,  like  the  latter,  insoluble  in  nitric 
acid.  Upon  heating  with  concentrated  solution  of  potassa,  phospha/te 
and  metastannate  of  potassa  are  formed. 

g.  Tribasic  phosphate  of  silver  is  a yellow  powder  ; it  is  insoluble  in 
water,  but  readily  soluble  in  nitric  acid,  and  also  in  ammonia.  In  am- 
moniacal  salts,  it  is  difficultly  soluble.  It  is  unalterable  in  the  air. 
Upon  ignition,  it  acquires  transiently  a reddish-brown  color ; at  an  in- 
tense red  heat,  it  fuses  without  decomposition. 


3 Ag  O 347-91  83-05 

P 06  71-00  16-95 


418-91  100-00 

h.  Phosphate  of  suboxide  of  mercury. — This  compound  is  employed 
for  the  purpose  of  effecting  the  separation  of  phosphoric  acid  from  many 
bases,  after  H.  Hose’s  method. 

Phosphate  of  suboxide  of  mercury  presents  the  appearance  of  a white 
crystalline  mass,  or  of  a white  powder.  It  is  insoluble  in  water,  but 
dissolves  in  nitric  acid.  The  action  of  a red  heat  converts  it  into  fused 
phosphate  of  oxide  of  mercury,  with  evolution  of  vapor  of  mercury. 
Upon  fusion  with  alkaline  carbonates,  alkaline  phosphates  are  produced, 
and  mercury,  oxygen,  and  carbonic  acid  escape. 

i.  Phospho-molybdate  of  ammonia. — This  compound  also  serves  to 
effect  the  separation  of  phosphoric  acid  from  other  bodies  ; it  is  of  the 
utmost  importance  in  this  respect. 

Phospho-molybdate  of  ammonia  forms  a bright  yellow,  readily  subsi- 
ding precipitate.  Dried  at  100°,  it  has,  according  to  Seligsohn,  the  fol- 


lowing (average)  composition : — 

M olybdic  acid 90-744 

Phosphoric  acid 3*142 

Oxide  of  ammonium 3*570 

Water 2*544 


100-000  * 

In  the  pure  state,  it  dissolves  but  sparingly  in  cold  water  (1  in  10000 — 
Eggertz)  ; but  it  is  soluble  in  hot  water.  It  is  readily  soluble,  even  in 
the  cold,  in  caustic  alkalies,  alkaline  carbonates  and  phosphates,  chloride 
of  ammonium,  and  oxalate  of  ammonia.  It  dissolves  only  sparingly  in 
sulphate  of  ammonia,  nitrate  of  potassa,  and  chloride  of  potassium  ; and 
very  sparingly  in  nitrate  of  ammonia. 

It  is  soluble  in  sulphate  of  potassa  and  sulphate  of  soda,  chloride  of 

* From  the  varying-  results  of  different  analysts  it  is  plain  that  the  precipitate, 
prepared  under  apparently  the  same  circumstances,  has  not  always  exactly  the 
same  composition.  Sonnenschein  (Journ.  f.  prakt.  Chem.  53,  342)  found  in  the 
precipitate  dried  at  120°,  293 — 3 12  # P Ofl ; Lipowitz  (Pogg.  Anna!  109,  135),  in  the 
precipitate  dried  at  from  20  to  30°,  3*607  £ P Os ; Eggertz  (Journ.  f.  prakt.  Chem. 
79,  496),  3-7  to  3 8.  [Dietrich  (Fres.  Zeitschrift  fur  analyt.  Chem.  1866,  45)  says 
that  this  precipitate  contains  small  and  variable  quantities  of  admixed  molybdic 
acid.  He  finds,  however,  that  the  relation  between  P Ch  and  N H3  is  constantly 
that  of  Seligsohn’s  formula  (23  NH,OP  05)  + 15  (H  O,  4 Mo  03).  Dietrich  esti- 
mates P05  by  bringing  the  ppt.  into  the  azotometer. 


144 


FORMS. 


r§  93. 

sodium  and  chloride  of  magnesium,  and  sulphuric,  hydrochloric,  and 
nitric  acids  (both  concentrated  and  dilute).  Water,  containing  1 per  cent, 
of  common  nitric  acid,  dissolves  -g-jVo  (Eggertz).  Application  of  heat 
does  not  check  the  solvent  action  of  these  substances.  Presence  of  mo- 
lybdate of  ammonia  totally  changes  its  deportment  with  acid  fluids  : in 
presence  of  that  substance,  it  is  almost  insoluble  in  acids,  even  upon 
ebullition.  The  solution  of  the  phospho-molybdate  of  ammonia  in  acids 
is  probably  attended,  in  all  cases,  with  decomposition  and  with  separa- 
tion of  the  molybdic  acid,  which  cannot  take  place  in  the  presence  of 
molybdate  of  ammonia  (J.  Craw  *).  Tartaric  acid  and  similar  organic 
substances  entirely  prevent  the  precipitation  of  the  phospho-molybdate 
of  ammonia  (Eggertz). f In  the  presence  of  an  iodide,  instead  of  a yel- 
low precipitate,  a green  precipitate  or  a green  fluid  is  formed,  resulting 
from  the  reducing  action  of  the  hydriodic  acid  on  the  molybdic  acid  (J. 
W.  Bill  J).  Other  substances  which  reduce  molybdic  acid  have  of 
course  a similar  action. 

5.  Boracic  Acid. 

Borofluoride  of  Potassium  is  the  best  form  to  convert  boracic  acid 
into  for  the  purpose  of  the  direct  estimation  of  the  acid.  This  com- 
pound is  produced  by  mixing  the  solution  of  an  alkaline  borate  (the  po- 
tassa  salt  answers  best)  with  hydrofluoric  acid  in  excess,  in  a silver  or 
platinum  dish,  and  evaporating  to  dryness.  The  gelatinous  precipitate 
which  forms  in  the  cold,  dissolves  upon  application  of  heat,  and  sepa- 
rates from  the  solution  subsequently,  upon  evaporation,  in  small,  hard, 
transparent  crystals.  The  compound  has  the  formula  K El,  B El3.  It 
is  soluble  in  water  and  also  in  dilute  spirit  of  wine  ; but  strong  al- 
cohol fails  to  dissolve  it ; it  is  insoluble  also  in  concentrated  solution 
of  acetate  of  potassa.  It  may  be  dried  at  100°,  without  suffering  de- 
composition (Aug.  Stromeyer§). 


K 39-11  31-01 

B 11-00  8-72 

El  76-00  60-27 


126-11  100-00 

6.  Oxalic  Acid. 

When  oxalic  acid  is  to  be  directly  determined  it  is  usually  precipi- 
tated in  the  form  of  oxalate  of  lime  ; and  its  weight  is  inferred  from 
the  carbonate  of  lime  produced  from  the  oxalate  by  ignition.  Eor 
the  properties,  &c.,  of  carbonate  of  lime  and  of  oxalate  of  lime,  see 
§ 73. 

7.  Hydrofluoric  Acid. 

The  direct  estimation  of  hydrofluoric  acid  is  usually  effected  by 
weighing  the  acid  in  the  form  of  fluoride  of  calcium. 

* Chem.  Gaz.  1852,  216. 

f [Lipowitz  (Jahresbericht,  1860,  618)  recommends  a molybdic  solution  con- 
taming’  tartaric  acid  for  the  precipitation  of  P Oft. 

X Sillim.  Journ.,  July,  1858.  § Annal.  d.  Chem.  u.  Pharm.  100,  82. 


93.] 


ACIDS  OF  GROUP  I. 


145 


Fluoride  of  calcium  forms  a gelatinous  precipitate,  which  it  is  found 
difficult  to  wash.  If  digested  with  ammonia,  previous  to  filtration, 
it  is  rendered  denser  and  less  gelatinous.  It  is  not  altogether  insolu- 
ble in  water ; aqueous  solutions  of  the  alkalies  fail  to  decompose  it. 
It  is  very  slightly  soluble  in  dilute,  but  more  readily  in  concentrated 
hydrochloric  acid.  When  acted  upon  by  sulphuric  acid,  it  is  decom- 
posed, and  sulphate  of  lime  and  hydrofluoric  acid  are  formed.  Fluoride 
of  calcium  is  unalterable  in  the  air,  and  at  a red  heat.  Exposed  to  a 
very  intense  heat,  it  fuses.  Upon  intense  ignition  in  moist  air,  it  is 
slowly  and  partially  decomposed  into  lime  and  hydrofluoric  acid. 
Mixed  with  chloride  of  ammonium,  and  exposed  to  a red  heat,  fluoride 
of  calcium  suffers  a continual  loss  of  weight ; but  the  decomposition  is 
incomplete. 


Ca 20  51*28 

FI 19  48-72 


39  100-00 

8.  Carbonic  Acid. 

The  direct  estimation  of  carbonic  acid — which,  however,  is  only 
rarely  resorted  to — is  usually  effected  by  weighing  the  acid  in  the 
form  of  carbonate  of  lime.  For  the  properties  of  the  latter  sub- 
stance, see  § 73. 

9.  Silicic  Acid  (or  Silica). 

By  whatever  decomposition  silicic  acid  is  separated  in  the  wet  way,  it 
is  always  hydrated.  The  hydrate  is  generally  gelatinous,  occasionally  pul- 
verulent. The  amount  of  water  it  contains  varies  according  to  the  cir- 
cumstances under  which  it  was  formed  ; at  least  this  is  the  only  explana- 
tion I can  give  of  the  great  differences  in  the  results  obtained  by  va- 
rious chemists  who  have  analyzed  hydrates  of  silicic  acid  dried  in  the 
same  way.* 

The  gelatinous  hydrate  of  silicic  acid  is  never  entirely  insoluble  in 
water  and  acids.  While  however  the  degree  of  solubility  is  relatively 
high,  if  the  hydrate  immediately  on  separation  comes  in  contact  with 
large  quantities  of  fluid,  it  is,  on  the  contrary,  low,  when,  after  having 
been  separated  and  washed,  it  is  treated  with  solvents ; thus  1 part  of 
silicic  acid  in  the  hydrated  condition,  obtained  by  passing  fluosilicic  gas 
into  water  and  washing  the  precipitate  completely,  requires  7700 
parts  of  water,  11000  parts  of  cold,  and  5500  parts  of  boiling  hydro- 
chloric acid  of  1-115  sp.  gr.  (J.  Fuchs,  loc.  cit.)  Hydrate  of  silicie 
acid  dried  at  100°  forms  a loose,  white  powder  ; it  is  insoluble  in  water 
and  in  acids  (hydrofluoric  excepted),  but  it  dissolves  in  solutions  of  the 
fixed  alkalies  and  their  carbonates,  especially  in  the  heat.  The  silicic 


* Doveri  (Anna!  de  Chim.  et  de  Phys.  21,  40  ; Anna!  d.  Chem.  u.  Pharm.  64, 
256)  found  in  the  air-dried  hydrate  16  9 to  17*8  & water  ; J.  Fuchs  (Anna!  d. 
Chem.  u.  Pharm.  82,  119  to  123),  91  to  9 6;  G.  Lippert  (Expt  No.  61),  9 28  to 
9-95.  Doveri  found  in  the  hydrate  dried  at  100°,  8 3 to  9 4 ; J.  Fuchs,  6 63  to 
6 96  ; G Lippert,  4 97  to  5 52  ; H.  Rose  (Pogg  Anna!  108,  1 ; Joum.  fur  prakt. 
Chem.  81,  227)  found  in  the  hydrate  obtained  by  digesting  stilbite  with  concen- 
trated hydrochloric  acid,  and  dried  at  150°,  4*85  £ water. 

10 


FORMS. 


146 


[§  91- 


acid  is  obtained  in  the  same  form,  when  its  solution  in  water  or  in  hy- 
drochloric acid  is  evaporated  and  the  residue  dried  at  100°. 

On  ignition  all  the  hydrates  pass  into  the  anhydrous  acid.  As  the 
vapoi  escapes  small  particles  of  the  extremely  fine  powder  are  liable  to 
whirl  up.  This  may  be  avoided  by  moistening  the  hydrate  in  the  cru- 
cible with  water,  evaporating  to  dryness  on  a water  bath,  and  then 
applying  at  first  a slight  and  then  a gradually  increased  heat. 

The  silicic  acid  obtained  by  igniting  the  hydrate  appears  in  the  amor- 
phous condition,  with  a sp.  gr.  of  2*2  to  2 ‘3.  It  forms  a white  powder 
insoluble  in  water  and  acids  (hydrofluoric  excepted),  soluble  in  solu- 
tions of  the  fixed  alkalies  and  their  carbonates,  especially  in  the  heat. 
Hydrofluoric  acid  readily  dissolves  amorphous  silicic  acid  ; the  solution 
leaves  no  residue  on  evaporation  in  platinum,  if  the  silica  was  pure. 
The  amorphous  silica,  when  heated  with  fluoride  of  ammonium  in  a 
platinum  crucible,  readily  volatilizes.  The  ignited  amorphous  silica, 
exposed  to  the  air,  eagerly  absorbs  water,  which  it  will  not  give  up  at 
from  100  to  150°.  (H.  Kose.)  Silica  fuses  at  the  strongest  heat.  The 

mass  obtained  is  vitreous  and  amorphous. 

Amorphous  silica  ignited  with  chloride  of  ammonium,  at  first  loses 
weight,  and  then,  when  the  ignition  has  rendered  it  denser,  'the  weight 
remains  constant. 

The  amorphous  silica  must  be  distinguished  from  the  crystallized  or 
crystalline  variety,  which  occurs  as  rock  crystal,  quartz,  sand,  &c.  This 
has  a sp.  gr.  of  2#6  (Schaffgotsch),  and  is  far  more  difficultly,  and  in 
far  less  amount,  dissolved  by  potash  solution  or  solution  of  fixed  alkaline 
carbonates ; it  is  also  more  slowly  attacked  by  hydrofluoric  acid  or  fluo- 
ride of  ammonium. 

Vegetable  colors  are  not  changed  either  by  silicic  acid  or  its  hydrates. 


Si 14*00  46-67 

02  16-00  53-33 


30-00  100-00 

ACIDS  OF  THE  SECOND  GROUP. 

§ 94. 

1.  Hydrochloric  Acid. 

Hydrochloric  acid  is  almost  invariably  weighed  in  the  form  of  chlo- 
ride of  silver — for  the  properties  of  which,  see  § 82. 

2.  Hydrobromic  Acid. 

Hydrobromic  acid  is  always  weighed  in  the  form  of  bromide  of  sil- 
ver. 

Bromide  of  silver , prepared  in  the  humid  way,  forms  a yellowish- 
white  precipitate.  It  is  wholly  insoluble  in  water  and  in  nitric  acid, 
tolerably  soluble  in  ammonia,  readily  soluble  in  hyposulphite  of  soda 
and  in  cyanide  of  potassium.  Concentrated  solutions  of  the  chlorides 
and  bromides  of  potassium,  sodium,  and  ammonium  dissolve  it  to  a very 
perceptible  amount,  while  in  very  dilute  solutions  of  these  salts  it  is 
entirely  insoluble.  Traces  only  dissolve  in  nitrates  of  the  alkalies.  On 
digestion  with  excess  of  iodide  of  potassium  solution  it  is  completely 


ACIDS  OF  GROUP  II. 


147 


§94.] 

converted  into  iodide  of  silver  (Field).  On  ignition  in  a current  of 
chlorine  the  bromide  of  silver  is  transformed  into  the  chloride ; on  igni- 
tion in  a current  of  hydrogen  it  is  converted  into  metallic  silver.  Ex- 
posed to  the  light  it  gradually  turns  gray,  and  finally  black.  Under  the 
influence  of  heat,  it  fuses  to  a reddish  liquid,  which,  upon  cooling,  solidi- 
fies to  a yellow  horn-like  mass.  Brought  into  contact  with  zinc  and 
water,  bromide  of  silver  is  decomposed : a spongy  mass  of  metallic  sil- 
ver forms,  and  the  solution  contains  bromide  of  zinc. 


Ag 107-97  57*44 

Br 80-00  42-56 


187-97  100-00 

3.  Hydriodic  Acid. 

Hydriodic  acid  is  usually  determined  in  the  form  of  iodide  of  sil- 
ver, and  occasionally  also  in  that  of  protiodide  of  palladium. 

a.  Iodide  of  silver,  produced  in  the  humid  way,  forms  a light-yellow 
precipitate,  insoluble  in  water  and  in  dilute  nitric  acid,  and  very  slightly 
soluble  in  ammonia.  One  part  dissolves,  according  to  Wallace  and 
Lamont,*  in  2493  parts  of  aqueous  ammonia  sp.  gr.  0*89,  according  to 
Martini,  in  2510  parts,  of  0*96  sp.  gr.  It  is  copiously  taken  up  by 
concentrated  solution  of  iodide  of  potassium,  but  it  is  insoluble  in  very 
dilute ; it  dissolves  readily  in  hyposulphite  of  soda  and  in  cyanide  of 
potassium ; traces  only  are  dissolved  by  alkaline  nitrates.  Hot  concen- 
trated nitric  and  sulphuric  acids  convert  it,  but  with  some  difficulty,  into 
nitrate  and  sulphate  of  silver  respectively,  with  expulsion  of  the  iodine. 
Iodide  of  silver  acquires  a black  color  when  exposed  to  the  light.  When 
heated,  it  fuses  without  decomposition  to  a reddish  fluid,  which,  upon 
cooling,  solidifies  to  a yellow  mass,  that  may  be  cut  with  a knife.  Un- 
der the  influence  of  excess  of  chlorine  in  the  heat  it  is  completely  con- 
verted into  chloride  of  silver ; ignition  in  hydrogen  reduces  it  to  the 
metallic  state.  When  brought  into  contact  with  zinc  and  water,  it  is 
decomposed : iodide  of  zinc  is  formed,  and  metallic  silver  separates. 


Ag 107-97  45-95 

1 127-00  54-05 


234-97  100-00 

b.  Protiodide  of  palladium , produced  by  mixing  an  alkaline  iodide 
with  protochloride  of  palladium,  is  a deep  brownish-black,  flocculent 
precipitate,  insoluble  in  water  and  in  dilute  hydrochloric  acid,  but 
slightly  soluble  in  saline  solutions  (chloride  of  sodium,  chloride  of  mag- 
nesium, chloride  of  calcium,  &c.).  It  is  unalterable  in  the  air.  Dried 
simply  in  the  air,  it  retains  one  equivalent  of  water  = 5*05  per  cent. 
Dried  long  in  vacuo , or  at  a rather  high  temperature  (70°  to  80°),  it 
yields  the  whole  of  this  water,  without  the  least  loss  of  iodine.  Dried 
at  100°,  it  loses  a trace  of  iodine;  at  from  300  to  400°,  the  whole  of 
the  iodine  is  expelled.  The  precipitated  iodide  of  palladium  may  be 
washed  with  hot  water,  without  loss  of  iodine. 


* Chem.  Gas.  1859,  137. 


148  forms.  [§  95. 

Pd 53-00  29-44 

1 127-00  70-56 

180-00  100-00 


4.  Hydrocyanic  Acid. 

Hydrocyanic  acid,  if  determined  gravimetrically  and  directly,  is 
always  converted  into  cyanide  of  silver — for  the  properties  of  which 
compound  see  § 82. 

5.  Hydrosulphuric  Acid  (or  Sulphuretted  Hydrogen). 

The  forms  into  which  sulphuretted  hydrogen,  or  the  sulphur  in  me- 
tallic sulphides,  is  converted  for  the  purpose  of  being  weighed,  are 
TERSULPHIDE  OF  ARSENIC,  SULPHIDE  OF  SILVER,  SULPHIDE  OF  COPPER,  and 
SULPHATE  OF  BARYTA. 

For  the  properties  of  the  sulphides  named,  see  §§  82,  85,  92 ; for 
those  of  sulphate  of  baryta,  see  § 71. 

ACIDS  OF  THE  THIRD  GROUP. 

§95. 

1.  Nitric  Acid;  and  2.  Chloric  Acid. 

These  two  acids  are  never  estimated  in  a direct  way — that  is  to  say, 
in  compounds  containing  them,  but  always  in  an  indirect  way ; generally 
volume  trically. 


SECTION  IV. 


THE  DETERMINATION  (OR  ESTIMATION)  OF  BODIES. 

§ 96. 

In  the  preceding  Section  we  have  examined  the  composition  and  proper- 
ties of  the  various  forms  and  combinations  in  which  bodies  are  separated 
from  others,  or  in  which  they  are  weighed.  We  have  now  to  consider 
the  special  means  and  methods  of  converting  the  several  bodies  into 
such  forms  and  combinations. 

For  the  sake  of  greater  clearness  and  simplicity,  we  shall,  in  the  pres- 
ent Section,  confine  our  attention  to  the  various  methods  applied  to  effect 
the  estimation  of  single  bodies , deferring  to  the  next  Section  the  consid- 
eration of  the  means  adopted  for  the  estimation  of  mixed  bodies,  or  the 
separation  of  bodies  from  one  another. 

We  have  to  deal  here  exclusively  with  bodies  in  the  free  state,  or 
with  compounds  consisting  of  one  base  and  one  acid , or  of  one  metal  and 
one  metalloid. 

As  in  the  u Qualitative  Analysis,”  the  acids  of  arsenic  will  be  treated 
of  among  the  bases,  on  account  of  their  behavior  to  sulphuretted  hydro- 
gen, and  those  elements  which  form  acids  with  hydrogen  will  be  con- 
sidered in  conjunction  with  their  respective  hydrogen  acids. 

In  the  quantitative  analysis  of  a body  we  have  to  study  first,  the  most 
appropriate  method  of  dissolving  it ; and,  secondly,  the  modes  of  deter- 
mining it. 

With  regard  to  the  latter  point,  we  have  to  turn  our  attention,  first, 
to  the  performance  / and  secondly,  to  the  accuracy  of  the  methods. 

It  happens  very  rarely  in  quantitative  analyses  that  the  amount  of  a 
substance,  as  determined  by  the  analytical  process,  corresponds  exactly 
with  the  amount  theoretically  calculated  or  actually  present ; and  if  it 
does  happen,  it  is  merely  by  chance. 

It  is  of  importance  to  inquire  what  is  the  reason  of  this  fact,  and  what 
are  the  limits  of  inaccuracy  in  the  several  methods. 

The  cause  of  this  almost  invariably  occurring  discrepancy  between 
the  quantity  present  and  that  actually  found,  is  to  be  ascribed  either 
exclusively  to  the  execution , or  it  lies  partly  in  the  method  itself. 

The  execution  of  the  analytical  processes  and  operations  can  never  be 
absolutely  accurate,  even  though  the  greatest  care  and  attention  be 
bestowed  on  the  most  trifling  minutiae.  To  account  for  this,  we  need 
only  bear  in  mind  that  our  weights  and  measures  are  never  absolutely 
correct,  nor  our  balances  absolutely  accurate,  nor  our  reagents  absolutely 
pure ; and,  moreover,  that  we  do  not  weigh  in  vacuo  y and  that,  even 
if  we  deduce  the  weight  in  vacuo  from  the  weight  we  actually  obtain  by 
weighing  in  the  air,  the  very  volumes  on  which  the  calculation  is  based 
are  but  approximately  known  ; — that  the  hygroscopic  state  of  the  air  is 


150 


DETERMINATION. 


[§  96. 

liable  to  vary  between  the  weighing  of  the  empty  crucible  and  of  the 
crucible  the  substance ; — that  we  know  the  weight  of  a filter  ash 
only  approximately  y — that  we  can  never  succeed  in  completely  keeping 
off  dust,  &c. 

With  regard  to  the  methods , many  of  them  are  not  entirely  free  from 
certain  unavoidable  sources  of  error  / — precipitates  are  not  absolutely  in- 
soluble ; compounds  which  require  ignition  are  not  absolutely  fixed ; 
others,  which  require  drying,  have  a slight  tendency  to  volatilize ; the 
final  reaction  in  volumetric  analyses  is  usually  produced  only  by  a small 
excess  of  the  standard  fluid,  which  is  occasionally  liable  to  vary  with  the 
degree  of  dilution,  the  temperature,  &c. 

Strictly  speaking,  no  method  can  be  pronounced  quite  free  from  defect ; 
it  should  be  borne  in  mind,  for  example,  that  even  sulphate  of  baryta  is 
not  absolutely  insoluble  in  water.  Whenever  we  describe  any  method  as 
free  from  sources  of  error,  we  mean,  that  no  causes  of  (considerable  in- 
accuracy are  inherent  in  it. 

We  have,  therefore,  in  our  analytical  processes,  invariably  to  contend 
against  certain  sources  of  inaccuracy  which  it  is  impossible  to  overcome 
entirely,  even  though  our  operations  be  conducted  with  the  most  scru- 
pulous care  and  with  the  utmost  attention  to  established  rules.  It  will 
be  readily  understood  that  several  defects  and  sources  of  error  may,  in 
some  cases,  combine  to  vitiate  the  results ; whereas,  in  other  cases,  they 
may  compensate  one  another,  and  thus  enable  us  to  attain  a higher  degree 
of  accuracy.  The  comparative  accuracy  of  the  results  attainable  by  an 
analytical  method  oscillates  between  two  points — these  points  are  called 
the  limits  of  error.  In  the  case  of  methods  free  from  sources  of  error, 
these  limits  will  closely  approach  each  other ; thus,  for  instance,  in  the 
estimations  of  chlorine,  with  great  care  one  will  always  be  able  to  obtain 
between  99‘9  and  100T  for  the  100  parts  of  chlorine  actually  present. 

Less  perfect  methods  -will,  of  course,  exhibit  far  greater  discrepan- 
cies ; thus,  in  the  estimation  of  strontia  by  means  of  sulphuric  acid,  the 
most  attentive  and  skilful  operator  may  not  be  able  to  obtain  more  than 
99-0  (and  even  less)  for  the  100  parts  of  strontia  actually  present.  I 
may  here  incidentally  state  that  the  numbers  occasionally  given  in  this 
manner,  in  the  course  of  the  present  work,  to  denote  the  degree  of  accu- 
racy of  certain  methods,  refer  invariably  to  the  substance  estimated 
(chlorine,  nitrogen,  baryta,  for  instance),  and  not  to  the  combination  in 
which  that  substance  may  be  weighed  (chloride  of  silver,  bichloride  of 
platinum  and  chloride  of  ammonium,  sulphate  of  baryta,  for  instance) ; 
otherwise  the  accuracy  of  various  methods  would  not  be  comparable. 

The  occasional  attainment  of  results  exactly  corresponding  with  the 
numbers  calculated  does  not  always  justify  the  assumption,  on  the  part 
of  the  student,  that  his  operations,  to  have  led  to  such  a result,  must 
have  been  conducted  with  the  utmost  precision  and  accuracy.  It  may 
sometimes  happen,  in  the  course  of  the  analytical  process,  that  one  error 
serves  to  compensate  another  ; thus,  for  instance,  the  analyst  may,  at  the 
commencement  of  his  operations,  spill  a minute  portion  of  the  substance 
to  be  analyzed ; whilst,  at  a later  stage  of  the  process,  he  may  recover 
the  loss  by  an  imperfect  washing  of  the  precipitate.  As  a general  rule, 
results  showing  a trifling  deficiency  of  substance  may  be  looked  upon  as 
better  proof  of  accurate  performance  of  the  analytical  process  than 
results  exhibiting  an  excess  of  substance. 

As  not  the  least  effective  means  of  guarding  against  error  and  inaccu' 


§97.] 


POTASSA. 


151 


racies  in  gravimetric  analyses , I would  most  strongly  recommend  the 
analyst,  after  weighing  a precipitate , &c.,  to  compare  its  properties  {color, 
solubility , reaction , <kc.)  with  those  which  it  should  possess , and  which 
have  been  amply  described  in  the  preceding  Section. 

In  my  own  laboratory,  I insist  upon  all  substances  that  are  weighed 
in  the  course  of  an  analysis  being  kept  between  watch-glasses,  until  the 
whole  affair  is  concluded.  This  affords  always  a chance  of  testing  them 
once  more  for  some  impurity,  the  presence  of  which  may  become  suspected 
in  the  after-course  of  the  process. 


I.  ESTIMATION  OF  BASES  IN  COMPOUNDS  CONTAINING  ONLY 
ONE  BASE  AND  ONE  ACID,  OR  ONE  METAL 
AND  ONE  METALLOID. 

FIRST  GROUP. 

POTASSA SODA AMMONIA — (lITHIA). 

8 97. 


1.  POTASSA. 

a.  Solution, 

Potassa  and  its  salts,  with  those  inorganic  acids  which  we  have  to  con- 
sider here,  are  dissolved  in  water,  in  which  menstruum  they  dissolve 
readily,  or  at  all  events,  pretty  readily. 

Potassa  salts  with  organic  acids  it  is  most  convenient  to  convert,  into 
sulphate  of  potassa.  See  p.  152. 

b.  Estimation. 

Potassa  is  weighed  either  as  sulphate  of  potassa,  as  chloride  of  potas- 
sium, or  as  bichloride  of  platinum  and  chloride  of  potassium  (see  § 68). 
For  the  alkalimetric  estimation  of  caustic  or  carbonated  potassa,  see 
§§  207  and  208. 

We  may  convert  into 

1.  Sulphate  of  Potassa. 

Salts  of  potassa  with  strong  volatile  acids ; e.g .,  chloride  of  potas- 
sium, bromide  of  potassium,  nitrate  of  potassa,  Ac.,  and  salts  with  or- 
ganic acids. 

2.  Chloride  of  Potassium. 

In  general,  caustic  potassa  and  salts  of  potassa  with  weak  volatile 
acids ; also,  and  more  particularly,  sulphate,  chromate,  chlorate,  and  sili- 
cate of  potassa. 

3.  Bichloride  of  Platinum  and  Chloride  of  Potassium. 

Salts  of  potassa  with  non-volatile  acids  soluble  in  alcohol ; e.g.,  phos- 
phate of  potassa,  borate  of  potassa. 

The  potassa  in  the  borate  of  that  alkali  may  be  determined  also  as 
sulphate  (§  136)  ; and  the  potassa  in  the  phosphate,  as  chloride  of  potas- 
sium (§  135). 


152 


DETERMINATION. 


The  form  of  bichloride  of  platinum  and  chloride  of  potassium  may  also 
be  resorted  to  in  general,  for  the  estimation  of  the  potassa  in  all  salts 
of  that  alkali  with  acids  soluble  in  alcohol.  This  form  is,  moreover,  of 
especial  importance,  as  that  in  which  the  separation  of  potassa  from 
soda,  <fec.,  is  effected. 

1.  Determination  as  Sulphate  of  Potassa. 

Evaporate  the  aqueous  solution  of  the  sulphate  of  potassa  to  dryness, 
ignite  the  residue  in  a platinum  crucible  or  dish,  and  weigh  (§  42).  The 
residue  must  be  thoroughly  dried  before  you  proceed  to  ignite  it ; the 
heat  applied  for  the  latter  purpose  must  be  moderate  at  first,  and  very 
gradually  increased  to  the  requisite  degree  ; the  crucible  or  dish  must 
be  kept  well  covered — neglect  of  these  precautionary  rules  involves 
always  a loss  of  substance  from  decrepitation.  If  free  sulphuric  acid  is 
present,  we  obtain,  upon  evaporation,  bisulphate  of  potassa ; in  such 
cases  the  excess  of  sulphuric  acid  is  to  be  removed  by  igniting  first  alone 
(here  it  is  best  to  place  the  lamp  so  that  the  flame  may  strike  the 
dish -cover  obliquely  from  above),  then  with  carbonate  of  ammonia. 
See  § 68. 

For  properties  of  the  residue,  see  § 68.  Observe  more  particularly 
that  the  residue  must  dissolve  to  a clear  fluid,  and  that  the  solution 
must  be  neutral.  Should  traces  of  platinum  remain  behind  (the  dish 
not  having  been  previously  weighed)  these  must  be  carefully  deter- 
mined, and  their  weight  subtracted  from  that  of  the  ignited  residue. 

With  proper  care  and  attention,  this  method  gives  accurate  results. 

To  convert  the  above-mentioned  salts  (chloride  of  potassium,  &c.) 
into  sulphate  of  potassa,  add  to  their  aqueous  solution  a quantity  of  pure 
sulphuric  acid  more  than  sufficient  to  saturate  the  whole  of  the  potassa, 
evaporate  the  solution  to  dryness,  ignite  the  residue,  and  convert  the 
bisulphate  of  potassa  into  the  neutral  salt,  by  treating  with  carbonate 
of  ammonia  (§  68). 

As  the  expulsion  of  a large  quantity  of  sulphuric  acid  is  a very  dis- 
agreeable process,  avoid  adding  too  great  an  excess.  Should  too  little 
of  the  acid  have  been  used,  which  you  may  infer  from  the  non-evolution 
of  sulphuric  acid  fumes  on  ignition,  moisten  the  residue  with  dilute 
sulphuric  acid,  evaporate,  and  again  ignite.  If  you  have  to  deal  with 
a small  quantity  only  of  chloride  of  potassium,  &c.,  proceed  at  once  to 
treat  the  dry  salt,  cautiously,  with  dilute  sulphuric  acid  in  the  platinum 
crucible  ; provided  the  latter  be  capacious  enough.  In  the  case  of 
bromide  and  iodide  of  potassium,  the  use  of  platinum  vessels  must  be 
avoided. 

[ Potassa  salts  with  organic  acids  are  directly  converted  into  sulphate 
of  potassa  by  first  carbonizing  them  at  the  lowest  possible  temperature, 
and  after  cooling  adding  some  crystals  of  pure  sulphate  of  ammonia  and  a 
little  water  to  the  mass.  The  crucible  being  covered,  the  water  is  eva- 
porated by  heating  the  crucible  cover,  and  the  whole  is  afterwards  heated 
to  dull  redness,  until  the  excess  of  sulphate  of  ammonia  is  destroyed. 
If  the  carbon  is  not  fully  consumed  by  this  operation,  add  a little  nitrate 
of  ammonia  and  repeat  the  ignition.  K'ammerer.*] 

2.  Determination  as  Chloride  of  Potassium. 

General  method  the  same  as  described  in  1.  The  residue  of  chloride 


[*  Fres.  Zeit.  VII.  222. J 


POTASSA* 


153 


§97.] 

of  potassium  must,  previously  to  ignition,  be  treated  in  the  same  way  as 
sulphate  of  potassa,  and  for  the  same  reason.  The  salt  must  be  heated 
in  a well-covered  crucible  or  dish,  and  only  to  dull  redness,  as  the  ap- 
plication of  a higher  degree  of  heat  is  likely  to  cause  some  loss  by  vola- 
tilization. No  particular  regard  need  be  had  to  the  presence  of  free 
acid.  For  properties  of  the  residue,  see  § 68.  This  method,  if  properly 
and  carefully  executed,  gives  very  accurate  results.  The  chloride  of 
potassium  may,  instead  of  being  weighed,  be  determined  volumetrically 
by  § 141,  b.  This  method,  however,  has  no  advantage  in  the  case  of 
single  estimations,  but  saves  time  when  a series  of  estimations  has  to  be 
made. 

In  determining  potassa  in  the  carbonate  it  is  sometimes  desirable  to 
avoid  the  effervescence  occasioned  by  treatment  with  hydrochloric  acid, 
as,  for  instance,  in  the  case  of  the  ignited  residue  of  a potassa  salt  with 
an  organic  acid,  which  is  contained  in  the  crucible.  This  may  be  effected 
by  treating  the  carbonate  with  solution  of  chloride  of  ammonium  in 
excess,  evaporating  and  igniting,  when  carbonate  of  ammonia  and  the 
excess  of  chloride  of  ammonium  will  escape,  leaving  chloride  of  potas- 
sium behind. 

The  methods  of  converting  into  chloride  of  potassium  the  potassa  com- 
pounds specified  above,  will  be  found  in  Part  II.  of  this  Section,  under 
the  respective  heads  of  the  acids  which  they  contain. 

3.  Determination  as  Dichloride  of  Platinum  and  Chloride  of  Potas- 
sium. 

a.  Salts  of  potassa  with  volatile  acids  (nitric  acid,  acetic  acid,  &c.). 

Mix  the  solution  with  hydrochloric  acid,  evaporate  to  dryness,  dis- 
solve the  residue  in  a little  water,  add  a concentrated  solution  of  bichlo- 
ride of  platinum,  as  neutral  as  possible,  in  excess,  and  evaporate  in  a 
porcelain  dish,  on  the  water-bath,  nearly  to  dryness,  taking  care  not  to 
heat  the  water-bath  quite  to  boiling.  Pour  spirit  of  wine  of  about  80  per 
cent,  over  the  residue  ; let  it  stand  for  some  time,  and  then  transfer  the 
bichloride  of  platinum  and  chloride  of  potassium,  which  remains  undis- 
solved, to  a weighed  filter  (which  may  be  readily  done  by  means  of  a 
washing  bottle  filled  with  spirit  of  wine).  Wash  with  spirit  of  wine, 
dry  at  100°,  and  weigh  (§  50). 

/S’.  Potassa  salts  with  non-volatile  acids  (phosphoric  acid,  boracic 
acid,  &b.). 

Make  a concentrated  solution  of  the  salt  in  water,  add  some  hydro- 
chloric acid,  and  bichloride  of  platinum  in  excess,  mix  with  a tolerable 
quantity  of  the  strongest  alcohol,  let  the  mixture  stand  24  hours  ; after 
which  filter,  and  proceed  as  directed  in  a. 

Properties  of  the  precipitate,  § 68.  This  method,  if  properly  execut- 
ed, gives  satisfactory  results.  Still  there  is  generally  a trifling  loss  of 
substance,  bichloride  of  platinum  and  chloride  of  potassium  not  being  ab- 
solutely insoluble  even  in  strong  alcohol.  In  accurate  analyses,  there- 
fore, the  alcoholic  washings  must  be  evaporated,  with  addition  of  a little 
pure  chloride  af  sodium,  at  a temperature  not  exceeding  75°,  nearly  to 
dryness,  and  the  residue  treated  once  more  with  spirit  of  wine.  A trifling 
additional  amount  of  bichloride  of  platinum  and  chloride  of  potassium 
is  thus  obtained,  which  is  either  added  to  the  principal  precipitate  or 
collected  on  a separate  small  filter,  and  determined  as  platinum,  by  the 
method  given  below.  The  object  of  the  addition  of  a little  chloride  of 


154 


DETERMINATION. 


[§  98« 


sodium,  to  the  bichloride  of  platinum  is  to  obviate  the  decomposition  to 
'which  pure  bichloride  of  platinum  is  more  liable,  upon  evaporation  in 
alcoholic  solution,  than  the  bichloride  containing  sodio-bichloride  of  pla- 
tinum. The  atmosphere  of  a laboratory  often  contains  ammonia,  which 
might  give  rise  to  the  formation  of  some  chloride  of  platinum  and 
ammonium,  and  to  a consequent  increase  of  weight  in  the  potassium 
salt. 

As  collecting  a precipitate  upon  a weighed  filter  is  a rather  tedious 
process,  and,  besides,  not  over  accurate,  where  we  have  to  deal  with 
minute  quantities  of  substance,  it  is  better  to  collect  small  portions  (up 
to  about  0'03  grm.)  of  bichloride  of  platinum  and  chloride  of  potassium 
upon  a very  small  unweiglied  filter, — dry,  and  transfer  the  filter,  with 
the  precipitate  wrapped  up  in  it,  to  a small  porcelain  crucible.  Cover 
the  crucible,  and  let  the  filter  slowly  char ; remove  the  cover,  burn  the 
carbon  of  the  filter,  and  let  the  crucible  get  cold.  Put  now  a very 
minute  portion  of  pure  oxalic  acid  into  the  crucible,  cover,  and  ignite, 
gently  at  first,  finally  to  a strong  red  heat.  The  addition  of  the  oxalic 
acid  greatly  promotes  the  complete  decomposition  of  the  bichloride  of 
platinum  and  chloride  of  potassium,  which  cannot  well  be  effected  by 
simple  ignition.  Treat  the  contents  of  the  crucible  now  with  water,  and 
wash  the  residuary  platinum,  until  the  last  rinsings  remain  clear  upon 
addition  of  solution  of  nitrate  of  silver.*  Dry  the  residuary  platinum, 
ignite,  and  weigh.  One  equivalent  of  platinum,  represents  one  equiva- 
lent of  potassium. 


§98. 

2.  Soda. 

a.  Solution 

See  § 97,  a — solution  of  potassa — all  the  directions  given  in  that  place 
applying  equally  to  the  solution  of  soda  and  its  salts. 

b.  Determination. 

Soda  is  determined  either  as  sulphate  of  soda , as  chloride  of  sodium , 
or  as  carbonate  of  soda  (§  69).  For  the  alkalimetric  estimation  of  caus- 
tic soda,  and  carbonate  of  soda,  see  §§  207  and  208. 

We  may  convert  into 

1.  Sulphate  of  Soda;  2.  Chloride  of  Sodium. 

In  general  the  salts  of  soda  corresponding  to  the  salts  of  potassa 
specified  under  the  analogous  potash  compounds,  § 97. 

3.  Carbonate  of  Soda. 

Caustic  soda,  bicarbonate  of  soda,  and  salts  of  soda  with  organic  acids, 
also  nitrate  of  soda  and  chloride  of  sodium. 

In  the  borate  of  soda  the  alkali  is  estimated  best  as  sulphate  of  soda 
(§  136) ; in  the  phosphate,  as  chloride  of  sodium,  or  carbonate  of  soda 

(§ 135)-  . . . ... 

Salts  of  soda  with  organic  acids  are  determined  either,  like  the  corre- 
sponding potassa  compounds,  as  chloride,  or — by  preference — as  carbon- 
ate. (This  latter  method  is  not  so  well  adapted  for  salts  of  potassa.) 

* The  washing  of  the  residuary  platinum  may  generally  be  effected  by  simple 
decantation. 


SODA. 


155 


§98.1 

The  analyst  must  here  bear  in  mind,  that  when  carbon  acts  on  fusing 
carbonate  of  soda,  carbonic  oxide  escapes,  and  caustic  soda  in  not  incon- 
siderable quantity  is  formed. 

1.  Determination  as  Sulphate  of  Soda. 

If  alone  and  in  aqueous  solution,  evaporate  to  dryness,  ignite  and 
weigh  the  residue  in  a covered  platinum  crucible  (§  42).  The  process 
does  not  involve  any  risk  of  loss  by  decrepitation,  as  in  the  case  of  sul- 
phate of  potassa.  If  free  sulphuric  acid  happens  to  be  present,  this  is 
removed  in  the  same  way  as  in  the  case  of  sulphate  of  potassa. 

With  regard  to  the  conversion  of  chloride  of  sodium,  &c.,  into  sul- 
phate of  soda,  see  § 97,  b , 1.  For  properties  of  the  residue,  see  § 69. 
The  method  is  easy,  and  gives  accurate  results. 

2.  Determination  as  Chloride  of  Sodium. 

Same  method  as  described  in  1.  The  rules  given  and  the  observations 
made  in  § 97,  b,  2,  apply  equally  here.  For  properties  of  the  residue 
see  § 69. 

The  methods  of  converting  the  sulphate,  chromate,  chlorate,  and  sili- 
cate of  soda  into  chloride  of  sodium,  will  be  found  in  Part  II.  of  this 
Section,  under  the  respective  heads  of  the  acids  which  these  salts  con- 
tain. 

3.  Determination  as  Carbonate  of  Soda. 

Evaporate  the  aqueous  solution,  ignite  moderately,  and  weigh.  The 
results  are  perfectly  accurate.  For  properties  of  the  residue,  see  § 69. 

Caustic  soda  is  converted  into  the  carbonate  by  adding  to  its  aqueous 
solution  carbonate  of  ammonia  in  excess,  evaporating  at  a gentle  heat, 
and  igniting  the  residue. 

Bicarbonate  of  soda,  if  in  the  dry  state,  is  converted  into  the  carbonate 
by  ignition.  The  heat  must  be  very  gradually  increased,  and  the  crucible 
kept  well  covered.  If  in  aqueous  solution,  it  is  evaporated  to  dryness, 
in  a capacious  silver  or  platinum  dish,  and  the  residue  ignited. 

Salts  of  soda  with  organic  acids  are  converted  into  the  carbonate  by 
ignition  in  a covered  platinum  crucible,  from  which  the  lid  is  removed 
after  a time.  The  heat  must  be  increased  very  gradually.  When  the 
mass  has  ceased  to  swell,  the  crucible  is  placed  obliquely,  with  the  lid 
leaning  against  it  (see  § 52,  fig.  42),  and  a dull  red  heat  applied  until 
the  carbon  is  consumed  as  far  as  practicable.  The  contents  of  the  cruci- 
ble are  then  warmed  with  water,  and  the  fluid  is  filtered  off  from  the 
residuary  carbon,  which  is  carefully  washed.  The  filtrate  and  rinsings 
are  evaporated  to  dryness  with  the  addition  of  a little  carbonate  of 
ammonia,  and  the  residue  is  ignited  and  weighed.  The  carbonate  of 
ammonia  is  added,  to  convert  any  caustic  soda  that  may  have  been 
formed  into  carbonate.  The  method,  if  carefully  conducted,  gives  accu- 
rate results ; however,  a small  loss  of  soda  on  carbonization  is  not  to  be 
avoided. 

Nitrate  of  soda,  or  chloride  of  sodium,  may  be  converted  into  car- 
bonate, by  adding  to  their  aqueous  solution  perfectly  pure  oxalic  acid  in 
moderate  excess,  and  evaporating  several  times  to  dryness,  with  repeated 
renewal  of  the  water.  All  the  nitric  acid  of  the  nitrate  of  soda  escapes 
in  this  process,  (partly  decomposed,  partly  undecomposed) ; and  equally 
so  all  the  hydrochloric  acid  in  the  case  of  chloride  of  sodium.  If  the 
residue  is  now  ignited  until  the  excess  of  oxalic  acid  is  removed,  car- 
bonate of  soda  is  left. 


156 


DETERMINATION. 


§99 

3.  Ammonia. 


a.  Solution. 

Ammonia  is  soluble  in  water,  as  are  all  its  salts  with  those  acids 
which  claim  our  attention  here.  It  is  not  always  necessary,  however, 
to  dissolve  the  ammoniacal  salts  for  the  purpose  of  determining  the 
amount  of  ammonia  contained  in  them. 

b.  Determination. 

Ammonia  is  weighed,  as  stated  § 70,  either  in  the  form  of  chloride 
of  ammonium , or  in  that  of  bichloride  of  platinum  and  chloride  of 
ammonium.  Into  these  forms  it  may  be  converted  either  directly  or 
indirectly  ( i.e .,  after  expulsion  as  ammonia,  and  re-combination  with 
an  acid).  Ammonia  is  also  frequently  determined  by  volumetric  an- 
alysis, and  its  quantity  is  sometimes  inferred,  from  the  volume  of  ni- 
trogen. 

We  convert  directly  into 

1.  Chloride  of  Ammonium. 

Ammoniacal  gas  and  its  aqueous  solution,  and  also  ammoniacal  salts 
with  weak  volatile  acids  (carbonate  of  ammonia,  sulphide  of  ammonium, 
&c.). 

2.  Bichloride  of  Platinum  and  Chloride  of  Ammonium. 

Ammoniacal  salts  with  acids  soluble  in  alcohol,  such  as  sulphate  of 
ammonia,  phosphate  of  ammonia,  &c. 

3.  The  methods  based  on  the  expulsion  of  the  ammonia  from  its 
compounds,  and  also  that  of  inferring  the  amount  of  ammonia  from  the 
volume  of  nitrogen  eliminated  in  the  dry  way,  are  equally  applicable  to 
all  ammoniacal  salts. 

The  expulsion  of  ammonia  in  the  dry  way,  (by  ignition  with  soda- 
lime,)  and  the  estimation  of  that  alkali  from  the  volume  of  nitrogen 
eliminated  in  the  dry  way,  being  effected  in  the  same  manner  as  the  es- 
timation of  the  nitrogen  in  organic  compounds,  I refer  the  student  to 
the  Section  on  organic  analysis.  Here  I shall  only  give  the  methods 
based  upon  the  expulsion  of  ammonia  and  of  nitrogen  in  the  wet  way. 
For  the  alkalimetric  estimation  of  free  ammonia,  see  §§  207  and  208. 

1.  Determination  as  Chloride  of  Ammonium. 

Evaporate  the  aqueous  solution  of  the  chloride  of  ammonium  on  the 
water-bath,  and  dry  the  residue  at  100°  until  the  weight  remains  con- 
stant (§  42).  The  results  are  accurate.  The  volatilization  of  the  chlo- 
ride is  very  trifling.  A direct  experiment  gave  99*94  instead  of  100. 
(See  Expt.  15.)  The  presence  of  free  hydrochloric  acid  makes  no 
difference  ; the  conversion  of  caustic  ammonia  into  chloride  of  ammo- 
nium may  accordingly  be  effected  by  supersaturating  with  hydrochloric 
acid.  The  same  applies  to  the  conversion  of  the  carbonate,  with  this 
addition  only,  that  the  process  of  supersaturation  must  be  conducted  in 
an  obliquely-placed  flask,  and  the  mixture  heated  in  the  same,  till  the 
carbonic  acid  is  driven  off.  In  the  analysis  of  sulphide  of  ammonium 
we  proceed  in  the  same  way,  taking  care  simply,  after  the  expulsion  of 
the  sulphuretted  hydrogen,  and  before  proceeding  to  evaporate,  to  filter 


AMMONIA. 


157 


§ 99.] 

off  the  sulphur  which  may  have  separated.  Instead  of  weighing  the 
chloride  of  ammonium,  its  quantity  may  be  inferred  by  the  determi- 
nation of  its  chlorine  according  to  § 141,  b.  (Comp,  chloride  of  potas- 
sium, § 97,  b,  3). 

2.  Determination  as  Dichloride  of  Platinum  and  Chloride  of  Am- 
monium. 

cl.  Ammoniacal  salts  with  volatile  acids. 

Same  method  as  described  in  § 97,  b,  L cl  (bichloride  of  platinum 
and  chloride  of  potassium). 

j3.  Ammoniacal  salts  with  non-volatile  acids. 

Same  method  as  described  § 97,  bf  4,  j3  (bichloride  of  platinum  and 
chloride  of  potassium).  The  results  obtained  by  these  methods  are  ac- 
curate. 

If  you  wish  to  control  the  results,*  ignite  the  double  chloride,  wrap- 
ped up  in  the  filter,  in  a covered  crucible,  and  calculate  the  amount  of 
ammonia  from  that  of  the  residuary  platinum.  The  results  must  agree. 
The  heat  must  be  increased  very  gradually,  f Want  of  due  caution  in 
this  respect  is  apt  to  lead  to  loss,  from  particles  of  the  double  salt 
being  carried  away  with  the  chloride  of  ammonium.  Very  small 
quantities  of  bichloride  of  platinum  and  chloride  of  ammonium  are 
collected  on  an  unweighed  filter,  dried,  and  at  once  reduced  to  platinum 
by  ignition.  J 

3.  Estimation  by  Expulsion  of  the  Ammonia  in  the  Wet  Way. 

This  method,  which  is  applicable  in  all  cases,  may  be  effected  in  two 

different  ways — viz., 

a.  Expulsion  of  the  Ammonia  by  distillation  with  Solution  of 
Potassa,  or  Soda,  or  with  Milk  of  Lime. —Applicable  in  all  cases 
where  no  nitrogenous  organic  matters  from  which  ammonia  might  be 
evolved  upon  boiling  with  solution  of  potassa,  etc.,  are  present  with  the 
ammonia  salts. 

Weigh  the  substance  under  examination  in  a small  glass  tube,  3 cen- 
timetres long  and  one  wide,  and  put  the  tube,  with  the  substance  in  it, 
into  a flask  containing  a suitable  quantity  of  moderately  concentrated 
solution  of  potassa  or  soda,  or  milk  of  lime,  from  which  every  trace  of 
ammonia  has  been  removed  by  protracted  ebullition,  but  which  has 
been  allowed  to  get  thoroughly  cold  again ; place  the  flask  in  a slanting 
position  on  wire-gauze,  and  immediately  connect  it  by  means  of  a glass 
tube  bent  at  an  obtuse  angle,  with  the  glass  tube  of  a small  cooling  ap- 
paratus. Connect  the  lower  end  of  this  tube,  by  means  of  a tight-fit- 
ting perforated  cork,  with  a sufficiently  large  tubulated  receiver  which 
is  in  its  turn  connected  with  a U tube  by  means  of  a bent  tube  passing 
through  its  tubulure. 


* If  the  bichloride  of  platinum  and  chloride  of  ammonium  is  pure,  which 
may  be  known  by  its  color  and  general  appearance,  this  control  may  be  dis- 
pensed with. 

\ The  best  way  is  to  continue  the  application  of  a moderate  heat  for  a 
long  time,  then  to  remove  the  lid,  place  the  crucible  obliquely,  with  the  lid 
leaning  against  it,  and  bum  the  charred  filter  at  a gradually  increased  heat  (H. 
Rose). 

X In  a series  of  experiments  to  get  the  platinum  from  pure  and  perfectly 
anhydrous  ammonio- bichloride  of  platinum,  by  very  cautious  ignition,  Mr. 
Lucius,  one  of  my  pupils,  obtained  from  44*1  to  44  3 per  cent,  of  the  metal,  in 
stead  of  44  3. 


158 


DETERMINATION. 


If  you  wish  to  determine  volumxtrically  the  quantity  of  ammonia  ex- 
pelled, introduce  the  larger  portion  of  a measured  quantity  of  standard 
solution  of  sulphuric  or  of  nitric  acid  (§  204),  into  the  receiver,  the  re- 
mainder into  the  U tube  ; add  to  the  portion  of  fluid  in  the  latter  a 
little  water,  and  color  the  liquids  in  the  receiver  and  U tube  red  with  1 
or  2 c.  c.  of  tincture  of  litmus.  The  cooling  tube  must  not  dip  into 
the  fluid  in  the  receiver ; the  fluid  in  the  U tube  must  completely  fill 
the  lower  part,  but  it  must  not  rise  high,  as  otherwise  the  passage  of 
air  bubbles  might  easily  occasion  loss  by  spirting.  The  quantity  of  acid 
used  must  of  course  be  more  than  sufficient  to  fix  the  whole  of  the  am- 
monia expelled. 

When  the  apparatus  is  fully  arranged,  and  you  have  ascertained  that 
all  the  joints  are  perfectly  tight,  heat  the  contents  of  the  flask  to  gentle 
ebullition,  and  continue  the  application  of  the  same  degree  of  heat  until 
the  drops,  as  they  fall  into  the  receiver,  have  for  some  time  altogether 
ceased  to  impart  the  least  tint  of  blue  to  the  portion  of  the  fluid  with 
which  they  first  come  in  contact.  Loosen  the  cork  of  the  flask,  allow  to 
stand  half  an  hour,  pour  the  contents  of  the  receiver  and  U tube  into  a 
beaker,  rinsing  out  with  small  quantities  of  water,  determine  finally 
with  a standard  solution  of  soda  the  quantity  of  acid  still  free,  which, 
by  simple  subtraction,  will  give  the  amount  of  acid  which  has  combined 
with  the  ammonia  ; and  from  this  you  may  now  calculate  the  amount  of 
the  latter  (§  204).  Results  accurate.* 

If  you  wish  to  determine  by  the  gravimetric  method  the  quantity  of 
ammonia  expelled,  receive  the  ammonia  evolved  in  a quantity  of  hydro- 
chloric acid  more  than  sufficient  to  fix  the  whole  of  it,  and  determine 
the  chloride  of  ammonium  formed,  either  by  simple  evaporation,  after 
the  directions  of  1,  or  as  ammonio-bicliloride  of  platinum,  after  the 
directions  of  2. 

b.  Expulsion  of  the  Ammonia  by  Milk  of  Lime,  without  Applica- 
tion of  Heat. — This  method,  recommended  by  Schlosing,  is  based  upon 
the  fact  that  an  aqueous  solution  containing  free  ammonia  gives  off*  the 
latter  completely,  and  in  a comparatively  short  time,  when  exposed  in 
a shallow  vessel  to  the  air,  at  the  common  temperature.  It  finds  appli- 
cation in  cases  where  the  presence  of  organic  nitrogenous  substances, 
decomposable  by  boiling  alkalies,  forbids  the  use  of  the  method  described 
in  3,  a ; thus,  for  instance,  in  the  estimation  of  the  ammonia  in  urine, 
manures,  &c. 

The  fluid  containing  the  ammonia,  the  volume  of  which  must  not 
exceed  35  c.  c.,  is  introduced  into  a shallow  flat-bottomed  vessel  from  10 
to  1 2 centimetres  in  diameter ; this  vessel  is  put  on  a plate  filled  with 
mercury.  A tripod,  made  of  a massive  glass  rod,  is  placed  in  the  vessel 
which  contains  the  solution  of  the  ammoniacal  salt,  and  a saucer  or 
shallow  dish  with  10  c.  c.  of  the  normal  solution  of  oxalic  or  sulphuric 
acid  (§  204)  put  on  it.  A beaker  is  now  inverted  over  the  whole.  The 
beaker  is  lifted  up  on  one  side  as  far  as  is  required,  and  a sufficient 
quantity  of  milk  of  lime  added  by  means  of  a pipette  (which  should  not 
be  drawn  out  at  the  lower  end).  The  beaker  is  then  rapidly  pressed 
down,  and  weighted  with  a stone  slab.  After  forty-eight  hours  the  glass 
is  lifted  up,  and  a slip  of  moist  reddened  litmus  paper  placed  in  it ; if 


* [In  thus  estimating  minute  quantities  of  ammonia,  the  condensing  tube 
must  be  of  tin,  since  glass  yields  a sensible  amount  of  alkali  to  hot  water  vapor.  ] 


AMMONIA. 


159 


§ 99.] 

no  change  of  color  is  observable,  this  is  a sign  that  the  expulsion  of  the 
ammonia  is  complete ; in  the  contrary  case,  the  glass  must  be  replaced. 
Instead  of  the  beaker  and  plate  with  mercury,  a bell-jar,  with  a ground 
and  greased  rim,  placed  air-tight  on  a level  glass  plate,  may  be  used.  A 
bell-jar,  having  at  the  top  a tubular  opening,  furnished  with  a close- 
fitting  glass  stopper,  answers  the  purpose  best,  as  it  permits  the  intro- 
duction of  a slip  of  red  litmus  paper  suspended  from  a thread  ; thus 
enabling  the  operator  to  see  whether  the  combination  of  the  ammonia 
with  the  acid  is  completed,  without  the  necessity  of  removing  the  bell- 
jar.  According  to  Schlosing,  forty-eight  hours  are  always  sufficient  to 
expel  OT  to  1 gramme  of  ammonia  from  25  to  35  c.  c.  of  solution. 
However,  I can  admit  this  statement  only  as  regards  quantities  up  to 
03  grm. ; quantities  above  this  often  require  a longer  time.  I,  there- 
fore, always  prefer  operating  with  quantities  of  substance  containing  no 
more  than  0‘3  grm.  ammonia  at  the  most. 

When  all  the  ammonia  has  been  expelled,  and  has  entered  into  com- 
bination with  the  acid,  the  quantity  of  acid  left  free  is  determined  by 
means  of  standard  solution  of  soda,  and  the  amount  of  the  ammonia 
calculated  from  the  result  (§  204). 

4.  Estimation  by  Expulsion  of  the  Nitro- 
gen in  the  Wet  Way. 

A process  for  determining  ammonia  by 
means  of  the  azotometer  has  been  given  by  W. 

Knop.*  It  depends  on  the  separation  of  the 
nitrogen  by  a bromized  and  strongly  alkaline 
solution  of  hypochlorite  of  soda.f 

[The  simplest  azotometer  is  that  described 
by  Humpf.^  It  consists  of  a burette  of  50  or 
100  c.  c.  stationed  in  a glass  cylinder  nearly 
filled  with  mercury,  and  connected  by  a stout 
caoutchouc  tube  with  a small  bottle,  «,  fig.  46, 
to  which  is  fitted  a soft  thrice-perforated  ca- 
outchouc stopper.  The  stopper  carries  a ther- 
mometer and  two  short  glass  tubes,  one  of 
which  joins  it  to  the  burette,  and  the  other 
has  attached  a short  bit  of  caoutchouc  tubing 
and  a pinch-cock,  e.  The  weighed  ammonia  salt 
(not  more  than  0*4  grm.)  is  placed  in  the  tube, 
f with  10  c.  c.  of  water,  and  50  c.  c.  of  the 
bromized  hypochlorite  solution  are  brought 
into  the  bottle,  a.  The  cock,  e,  being  open,  the 
stopper  is  firmly  fixed  in  its  place,  and  the 
burette  is  depressed  in  the  mercury  until  its 
uppermost  degree  exactly  coincides  with  the 
surface  of  the  metal.  The  cock  is  then  closed, 

* Chem.  Centralbl.  1860./  244. 

f This  is  prepared  as  follows : — Dissolve  1 part  of  carbonate  of  soda  in  15  parts 
of  water,  cool  the  fluid  with  ice,  saturate  perfectly  with  chlorine,  keeping  cold 
all  the  while,  and  add  strong  soda  solution  (of  25  per  cent . ) till  the  mixture  on 
rubbing  between  the  fingers  makes  the  skin  slippery.  Before  using,  add  to  the 
quantity  required  for  the  series  of  experiments  bromine  in  the  proportion  of  2-3 
grm.  to  the  litre,  and  shake. 

X Fres.  Zeit.,  YI.  398. 


TABLE  OF  THE  ABSORPTION  OF  NITROGEN  GAS 


160 


DETERMINATION. 


[§  100 


3 

I 

''to 

o 

§3 


Is  ? 
§ § 


o o 
I-I  o 

a 5* 
e a 


to  o 

1* 
^ o 
"8  ^ 
.**  a 

i t 

O ,— I 
S> 

rO  l—l 

V 


20 

0.53 

40 

1.03 

60 

1.53 

CO 

o o 
00  cq 

£G'Z 

001 

19 

0.51 

39 

1.01 

59 

1.51 

79 

2.01 

WZ 

66 

00 

00 

rH  d 

38 

0.98 

58 

1.48 

78 

1.98 

98 

2.48 

17 

0.46 

37 

0.96 

57 

1.46 

96T 

IL 

97 

2.46 

16 

0.43 

36 

0.93 

56 

1.43 

76 

1.93 

96 

2.43 

15 

0.41 

35 

0.91 

55 

1.41 

75 

1.91 

95 

2.41 

00 

^ CO 

1-1  d 

34 

0.88 

54 

1.38 

GO 

^ 00 

I-  ^ 

94 

2.38 

13 

0.36 

98*0 

€8 

53 

1.36 

73 

1.86 

93 

2.36 

12 

0.33 

32 

0.83 

52 

1.33 

72 

1.83 

92 

2.33 

11 

0.31 

31 

0.81 

51 

1.31 

71 

1.81 

l£'Z 

16 

10 

0.28 

30 

0.78 

50 

1.28 

70 

1.78 

8Z'Z 

06 

9 

0.26 

29 

0.76 

49 

1.26 

69 

1.76 

9Z’Z 

68 

8 

0.23 

28 

0.73 

48 

1.23 

68 

1.73 

88 

2.23 

7 

0.21 

27 

0.71 

47 

1.21 

67 

1.71 

87 

2.21 

00 

«o  ,-H. 
o 

26 

0.68 

46 

1.18 

89T 

99 

86 

2.18 

5 

0.16 

99*0 

QZ 

45 

1.16 

65 

1.66 

85 

2.16 

4 

0.13 

24 

0.63 

44 

1.13 

64 

1.63 

84 

2.13 

rH 

co  H 
o 

rH 

CO  o 
CN  o 

rH 

CO  r- 1 

^ i— ; 

CO  o 

50  rH* 

83 

2.11 

GO 

Cq  °. 

o 

00“ 
cq  io 
Oq  0* 

80T 

Zf 

oo 

cq  io 

00 

cq  o 
00  Cq 

1 

0.06 

21 

0.56 

41 

1.06 

61 

1.56 

81 

2.06 

Evolved 

Absorbed 

Evolved 

Absorbed 

Evolved 

Absorbed 

Evolved 

Absorbed 

Evolved 

Absorbed 

LITHIA. 


/ 


161 

and  the  bottle  is  inclined  to  bring  the  two  substances  in  contact.  The 
ammonia  salt  is  speedily  decomposed.  When  no  further  evolution  of  gas 
takes  place  the  burette  is  so  adjusted  that  the  level  of  the  mercury 
without  and  within  it  shall  nearly  coincide,  and  the  operator  waits 
10-20  minutes,  or  until  the  thermometer  in  a indicates  the  same  tem- 
perature as  the  surrounding  air.  Then  the  adjustment  of  the  burette  to 
exact  coincidence  of  the  mercury  level,  within  and  without,  is  effected, 
and  the  volume  of  the  gas  is  read  off.  The  stand  of  the  thermometer 
and  barometer  are  also  noted,  and  the  recorded  volume  of  nitrogen  is 
corrected  by  use  of  the  tables  on  pp.  160  and  162-163,  by  Dietrich: 

The  first  table  gives  a correction  for  the  nitrogen  which  is  absorbed 
by  the  60  c.  c.  of  liquid  in  the  bottle  a.  The  amount  varies  with  the 
relative  volumes  of  air  and  nitrogen,  and  is  determined  empirically  by 
decomposing  known  quantities  of  ammonia  and  noting  the  difference 
between  the  obtained  and  the  theoretical  volume  of  nitrogen.  The  cor- 
rection holds  strictly,  of  course,  only  for  a solution  of  such  strength  as 
that  employed  by  Dietrich  and  at  the  mean  temperatures. 

The  second  table  serves  to  spare  the  labor  of  calculation.  The  weight 
of  1 c.  c.  of  nitrogen,  measured  e.  g.  at  754  mm.  of  barometer  and  15°  C., 
is  found  at  the  intersection  of  the  vertical  column  754  with  the  hori- 
zontal column  15°,  is,  viz.,  1T6187. 

To  the  observed  volume  of  nitrogen  add  the  amount  absorbed  as  per 
Table  I.,  and  correct  the  total  by  Table  II.  It  scarcely  requires  to  be 
mentioned  that  good  results  can  only  be  obtained  in  an  apartment 
where  the  temperature  is  uniform,  and  when  care  is  exercised  to  avoid 
warming  the  apparatus  in  handling.  See  Dietrich’s  papers.* 


§ 100. 

Supplement  to  the  First  Group . 

LITHIA. 

In  the  absence  of  other  bases,  lithia  may,  like  potassa  and  soda,  be 
converted  into  anhydrous  sulphate,  and  weighed  in  that  form 
(Li  O,  S03).  As  lithia  forms  no  acid  sulphate,  the  excess  of  sulphuric 
acid  may  be  readily  removed  by  simple  ignition.  Carbonate  of  lithia 
also,  which  is  difficultly  soluble  in  water,  and  fuses  at  a red  heat  without 
suffering  decomposition,  is  well  suited  for  weighing ; whilst  chloride  of 
lithium,  which  deliquesces  in  the  -uir,  and  is  by  ignition  in  moist  air 
converted  into  hydrochloric  acid  and  lithia,  is  unfit  for  the  estimation 
of  lithia. 

In  presence  of  other  alkalies,  lithia  is  best  converted  into  basic  phos- 
phate of  lithia  (3  Li  O,  P 05),  and  weighed  in  that  form.  This  is 
effected  by  the  following  process : add  to  the  solution  a sufficient  quan- 
tity of  phosphate  of  soda  (which  must  be  perfectly  free  from  phosphates 
of  the  alkaline  earths),  and  enough  soda  to  keep  the  reaction  alkaline, 
and  evaporate  the  mixture  to  dryness ; pour  water  over  the  residue,  in 
sufficient  quantity  to  dissolve  the  soluble  salts  with  the  aid  of  a gentle 


* Fres.  Zeit.  III.  162.  ; IY.  141,  and  Y.  36. 
11 


Temperature  Celsius. 


162 


TABLE  OF  WEIGHTS. 


II.  TABLE  OF  THE  WEIGHT  OF  A 


In  Milligrammes  for  Pressures  from  720  to  770  mm. 

Millimetres. 


720 

722 

724 

726 

728 

730 

732 

734 

736 

738 

740 

742 

744 

10° 

1.13380 

1.13699 

1.14018 

1.14337 

1.14656 

1.14975 

1.15294 

1.15613 

1.15932 

1.16251 

1.16570 

1 1.16889 

1.17208 

11° 

1.12881 

1.13199 

1.13517 

1.13835 

1.14153 

1.14471 

1.14789 

1.15107 

1.15424 

1.15742 

1.16060 

1.16378 

1.16696 

12° 

1.12376 

1.12693 

1.13010 

1.13326 

1.13643 

1.13960 

1.14277 

1.14593 

1.14910 

1.15227 

1.15543 

1.15860 

1.16177 

13° 

1.11875 

1.12191 

1.12506 

1.12822 

1.13138 

1.13454 

1.13769 

1.14085 

1.14401 

1.14716 

1.15032 

1 

1.15348 

1.15663 

14° 

1.11369 

1.11684 

1.11999 

1.12313 

1.12628 

1.12942 

1.13257 

1.13572 

1.13886 

1.14201 

1.14515 

1.14830 

1.15145 

15° 

1.10859 

1.11172 

1.11486 

1.11799 

1.12113 

1.12426 

1.12739 

1.13053 

1.13366 

1.13680 

1.13993 

1.14306 

1.14620 

16° 

1.10346 

1.10658 

1.10971 

1.11283 

1.11596 

1.11908 

1.12220 

1.12533 

1.12845 

1.13158 

1.13470 

1.13782 

1.14095 

17° 

1.09828 

1.10139 

1.10450 

1.10761 

1.11073 

1.11384 

1.11695 

1.12006 

1.12317 

1.12629 

1.12940 

1.13251 

1.13562 

18° 

1.09304 

1.09614 

1.09924 

1.10234 

1.10544 

1.10854 

1.11165 

1.11475 

1.11785 

1.12095 

1.12405 

1.12715 

1.13025 

19° 

1.08744 

1.09083 

1.09392 

1.09702 

1.10011 

1.10320 

1.10629 

1.10938 

1.11248 

1.11557 

1.11866 

1.12175 

1.12484 

20° 

1.08246 

1.08654 

1.08862 

1.09170 

1.09478 

1.09786 

1.10094 

1.10402 

1.10710 

1.11018 

1.11327 

1.11635 

1.11943 

21° 

1.07708 

1.08015 

1.08322 

1.08629 

1.08936 

1.09243 

1.09550 

1.09857 

1.10165 

1.10472 

1.10779 

1.11086 

1.11393 

22° 

1.07166 

1.07472 

1.07778 

1.08084 

1.08390 

1.08696 

1.09002 

1.09308 

1.09614 

1.09921 

1.10227 

1.10533 

1.10839 

23° 

1.06616 

1.06921 

1.07226 

1.07531 

1.07&36 

1.08141 

1.08446 

1.08751 

1.09056 

1.09361 

1.09666 

1.09971 

1.10276 

24° 

1.06061 

1.06365 

1.06669 

1.06973 

1.07277 

1.07581 

1.07885 

1.08189 

1.08493 

1.08796 

1.09100 

1.09404 

1.09708 

25° 

1.05499 

1.05801 

1.06104 

1.06407 

1.06710 

1.07013 

1.07316 

1.07619 

1.07922 

1.08225 

1.08528 

1.08831 

1.09134 

720 

722 

724 

726 

728 

730 

732 

734 

736 

738 

740 

742 

744 

Millimetres. 


TABLE  OF  WEIGHTS. 


163 


CUBIC  CENTIMETRE  OF  NITROGEN. 

of  Mercury,  and  for  Temperatures  from  10°  to  25°  C. 

Millimetres. 


746 

748 

750 

752 

754 

756 

758 

760 

762 

764 

766 

768 

770 

1.17527 

1.17846 

1.18165 

1.18484 

1.18803 

1.19122 

1.19441 

1.19760 

1.20079 

1.20398 

1.20717 

1.21036 

1.21355 

10'5 

1.17014 

1.17332 

1.17650 

1.17168 

1.18286 

1.18603 

1.18921 

1.19239 

1.19557 

1.19875 

1.20193 

1.20511 

1.20829 

11° 

1.16493 

1.16810 

1.17127 

1.17444 

1.17760 

1.18077 

1.18394 

1.18710 

1.19027 

1.19344 

1.19660 

1.19977 

L 20294 

12® 

1.15979 

1.16295 

1.16611 

1.16926 

1.17242 

1.17558 

1.17873 

1.18189 

1.18505 

1.18820 

1.19136 

1 

1.19452 

1.19768 

13® 

1.15459 

1.15774 

1.16088 

1.16403 

1.16718 

1.17032 

1.17347 

1.17661 

1.17976 

1.18291 

1.18605 

1.18920 

1.19234 

14° 

1.14933 

1.15247 

1.15560 

1.15873 

1.16187 

1.16500 

1.16814 

1.17127 

1.17440 

1.17754 

1.18067 

1.18381 

1.18694 

15® 

1.14407 

1.14720 

1.15032 

1.15344 

1.15657 

1.15969 

1.16282 

1.16594 

1.16906 

1.17219 

1.17531 

1.17844 

1.18156 

16° 

1.13873 

1.14185 

1.14496 

1.14807 

1.15118 

1.15429 

1.15741 

1.16052 

1.16363 

1.16674 

1.16985 

1.17297 

1.17608 

17® 

1.13335 

1.13645 

1.13955 

1.14266 

1.14576 

1.14886 

1.15196 

1.15506 

1.15816 

1.16126 

1.16436 

1.16746 

1.17056 

18® 

1.12794 

1.13103 

1.13412 

1.13721 

1.14030 

1.14340 

1.14649 

1.14958 

1.15267 

1.15576 

1.15886 

1.16195 

1.16504 

19® 

1.12251 

1.12559 

1.12867 

1.13175 

1.13483 

1.13791 

1.14099 

1.14408 

1.14716 

1.15024 

1.15332 

1.15640 

1.15948 

20° 

1.11700 

1.12007 

1.12314 

1.12621 

1.12928 

1.13236 

1.13543 

1.13850 

1.14157 

1.14464 

1.14771 

1.15078 

1.15385 

21® 

1.11145 

1.11451 

1.11757 

1.12063 

1.12369 

1.12675 

1.12982 

1.13288 

1.13594 

1.13900 

1.14206 

1.14512 

1.14818 

22° 

1.10581 

1.10886 

1.11191 

1.11496 

1.11801 

1.12106 

1.12411 

1.12716 

1.13021 

1.13326 

1.13631 

1.13936 

1.14241 

23® 

1.10012 

1.10316 

1.10620 

1.10924 

1.11228 

1.11532 

1.11835 

1.12139 

1.12443 

1.12747 

1.13051 

1.13355 

1.13659 

24® 

1.09437 

1.09740 

1.10043 

1.10346 

1.10649 

1.10952 

1.11255 

1.11558 

1.11861 

1.12164 

1.12467 

1.12770 

1.13073 

25® 

746 

748 

750 

752 

754 

756 

758 

760 

762 

764 

766 

768 

770 

Millimetres. 


Temperature  Celsius. 


164 


DETERMINATION. 


[§  101. 


heat,  add  an  equal  volume  of  solution  of  ammonia,  digest  at  a gentle 
heat,  filter  after  twelve  hours,  and  wash  the  precipitate  with  a mixture 
of  equal  volumes  of  water  and  solution  of  ammonia.  Evaporate  the 
filtrate  and  first  washings  to  dryness,  and  treat  the  residue  in  the  same 
way  as  before.  If  some  more  phosphate  of  lithia  is  thereby  obtained, 
add  this  to  the  principal  quantity.  The  process  gives,  on  an  average, 
99*61  for  100  parts  of  lithia. 

If  the  quantity  of  lithia  present  is  relatively  very  small,  the  larger  por- 
tion of  the  potassa  or  soda  compounds  should  first  be  removed  by  addi- 
tion of  absolute  alcohol  to  the  most  highly  concentrated  solution  of 
the  salts  (chlorides,  bromides,  iodides,  or  nitrates,  but  not  sulphates)  ; 
since  this,  by  lessening  the  amount  of  water  required  to  effect  the  separa- 
tion of  the  phosphate  of  lithia  from  the  soluble  salts,  will  prevent  loss  of 
lithia  (W.  Mayer*). 

The  precipitated  basic  phosphate  of  lithia  has  the  formula  3 Li  O, 
P Os  + aq.  It  dissolves  in  2539  parts  of  pure,  and  3920  parts  of  ammo- 
niated  water ; at  100°,  it  completely  loses  its  water ; if  pure,  it  does  not 
cake  at  a moderate  red  heat  (Mayer). 

The  objections  raised  by  Bammelsberg  f to  Mayer’s  method  of  estima- 
ting lithia  I find  to  be  ungrounded.  According  to  my  own  experience, 
it  appears  that  .the  filtrate  and  wash- water  must  be  evaporated  in  a plati- 
num dish  not  only  once,  but  at  least  twice — in  fact,  till  a residue  is 
obtained  which  is  completely  soluble  in  dilute  ammonia.  Phosphate  of 
lithia  may  be  dried  at  100°,  or  ignited  according  to  § 53,  before  being 
weighed.  In  the  latter  case,  care  must  be  taken  to  free  the  filter  as  much 
as  possible  from  the  precipitate  before  proceeding  to  incinerate  it.  I have 
thus  obtained,  J instead  of  100  parts  carbonate  of  lithia,  by  drying  at 
100°,  99*84,  99*89,  100*41, — by  igniting  99*66  and  100*05.  The  phos- 
phate of  lithia  obtained  was  free  from  soda. 


SECOND  GROUP. 

BARYTA STRONTIA LIME MAGNESIA. 

§ 101. 

1.  Baryta. 


a.  Solution . 

Caustic  baryta  is  soluble  in  water,  as  are  many  of  the  salts  of  this  alka- 
line earth.  The  salts  of  baryta  which  are  insoluble  in  water  are,  with  al- 
most the  single  exception  of  the  sulphate,  readily  dissolved  by  dilute 
hydrochloric  acid.  The  solution  of  the  sulphate  is  effected  by  fusion  with 
carbonate  of  soda,  &c.  (See  § 132.) 

b.  Determination. 

Baryta  is  weighed  either  as  sulphate  or  as  carbonate , rarely  (in  the  sepa- 


* Anna!  derChem.  u.  Pharm.  98,193,  where  Mayer  has  also  demonstrated  the 
non-existenoe  of  a phosphate  of  soda  and  lithia  of  fixed  composition  (Berzelius), 
or  of  varying  composition  (Rammelsberg). 
f Pogg.  Anna!  102,  443. 

\ Zeitschr.  f.  Analyt.  Chem.  1,42. 


[Reprint  from  the  American  Chemist  of  Feb.  1875.] 


FABLE  FOR  THE  <L 

SULTS  OBTAINED  ON  MINERAL  AND 
POTABLE  WATERS. 


BY  E.  WALLER,  A.M.,  E.M. 

The  following  table  may  be  found  of  use  in  the 
analysis  of  mineral  and  potable  waters  for  the  calcula- 
tion of  the  number  of  grains  in  the  U.  S.  gallon  of 
231  cubic  inches,  the  number  of  milligrammes  per  litre 
having  been  found.  The  number  of  grains  in  the  gal- 
lon has  been  taken  as  58,318,  which  is  believed  to  be 
the  most  correct  figure,  though  authorities  on  the  sub. 
ject  differ  slightly  from  one  another,  e.  g.,  the  U.  S.  Dis- 
pensatory gives  58,328*886,  or  nearly  11  grains  more.* 
Either  of  these  results  gives  about  133*3  avoirdupois 
ounces  in  the  gallon. 

Table  showing  the  number  of  grains  in  the  U.  S. 
gallon  of  231  cubic  inches,  corresponding  to  the  num- 
ber of  milligrammes  in  one  litre. 

Mgs.  to  1 litre  = grs.  to  U.  S.  gal.  Mgs.  to  1 litre  = grs.  to  U.  S.  gal. 


I 

0*058318 

2 

0*116636 

3 

0*174954 

4 

0*233272 

5 

0291 590 

6 

0*349908 

7 

0*408226 

8 

0*466544 

9 

0*524862 

10 

0*583180 

11 

0*641498 

12 

0*699816 

13 

o*758i34 

14 

0*816452 

15 

0*874770 

16 

0*933088 

17 

0*991406 

18 

1*049724 

19 

1*108042 

20 

1*166360 

21 

1*224678 

22 

1*282996 

23 

I'34i3i4 

24 

1*399632 

25 

1*457950 

26 

1*516268 

27 

1*574586 

28 

1*632904 

29 

1*691222 

30 

1*749540 

31 

1*807858 

32 

1*866176 

33 

1*924494 

34 

1*982812 

35 

2*041 130 

36 

2*099448 

37 

2*157766 

38 

2*216084 

39 

2*274502 

40 

2*332720 

4i 

2*391038 

42 

2*449356 

43 

2*507674 

44 

2*565992 

45 

2*624310 

46 

2*682628 

47 

2*740946 

48 

2*799264 

49 

2*857582 

50 

2*9!  59°o 

5i 

2*974218 

52 

3*032536 

53 

3*090854 

54 

3*149172 

55 

3*207490 

56 

3*265808 

57 

3*324126 

58 

3-382444 

59 

3*440762 

60 

3*499080 

61 

3-557398 

62 

3-615716 

63 

3*674034 

64 

3-732352 

65 

3*790670 

66 

3*848988 

67 

3-907306 

68 

3*965624 

69 

4023942 

70 

4*082260 

7 1 

4*140578 

72 

4*198896 

73 

4*257214 

74 

4-3I5532 

75 

4-37385° 

76 

4-432168 

77 

4*490486 

78 

4*548804 

79 

4*607122 

80 

4*665440 

81 

4*723758 

82 

4782076 

83 

4*840394 

84 

4*898712 

85 

4*957030 

86 

5*0!  5348 

87 

5*073666 

88 

5*i3i984 

89 

5*190302 

90 

5*248620 

9i 

5*306938 

92 

5-365256 

93 

5-423574 

94 

5*481892 

95 

5*540210 

96 

5*598528 

97 

5*656846 

98 

5*715164 

99 

5*773482 

100 

5*831800 

* See  discussion  of  this  point  by  W.  H.  Chandler,  Am.  Chem.  I.  318. 


BARYTA. 


1G5 


101.] 


ration  from  strontia)  as  silico-fuoride  of  barium,  (§  71).  Baryta  in  the 
pure  state,  or  in  form  of  carbonate,  may  also  be  determined  by  the  volu- 
metric (alkalimetric)  method.  Comp.  § 210. 

We  may  convert  into 


1.  Sulphate  of  Baryta. 

a.  By  Precipitation.  b.  By  Evaporation. 

All  compounds  of  baryta  without  All  compounds  of  baryta  with 
exception.  volatile  acids,  if  no  other  non-vola- 

tile body  is  present. 

2.  Carbonate  of  Baryta. 

a.  All  salts  of  baryta  soluble  in  water. 

b.  Salts  of  baryta  with  organic  acids. 

Baryta  is  both  precipitated  and  weighed,  by  far  the  most  frequently  as 
sulphate,  the  more  so  as  this  is  the  form  in  which  it  is  most  conveniently 
separated  from  other  bases.  The  determination  by  means  of  evaporati<  >n 
(1,  b)  is,  in  cases  where  it  can  be  applied,  and  where  we  are  not  obliged  to 
evaporate  large  quantities  of  fluid,  very  exact  and  convenient.  Baryta  is 
determined  as  carbonate  in  the  wet  way,  when  from  any  reason  it  is  not 
possible  or  not  desirable  to  precipitate  it  as  sulphate.  If  a fluid  or  dry 
substanee  contains  bodies  which  impede  the  precipitation  of  the  baryta  as 
sulphate  or  carbonate  (alkaline  citrates,  metaphosphoric  acid,  see  § 71, 
a and  b ),  such  bodies  must  of  course  be  got  rid  of,  before  proceeding  to 
precipitation. 

1.  Determination  as  Sulphate  of  Baryta. 

a.  By  Precipitation. 

Heat  the  moderately  dilute  solution  of  baryta,  which  must  not  contain 
too  much  free  acid  (and  must,  therefore,  if  necessary,  first  be  freed  there- 
from by  evaporation  or  addition  of  carbonate  of  soda),  in  a platinum  or 
porcelain  dish,  or  in  a glass  vessel,  to  incipient  ebullition,  add  dilute  sul- 
phuric acid,  as  long  as  a precipitate  forms,  keep  the  mixture  for  some  time 
at  a temperature  very  near  the  boiling  point,  and  allow  the  precipitate  a 
few  minutes  to  subside  ; decant  the  almost  clear  supernatant  fluid  on  a 
filter,  boil  the  precipitate  three  or  four  times  \yith  water,  then  transfer  it 
to  the  filter,  and  wash  with  boiling  water,  until  the  filtrate  is  no  longer 
rendered  turbid  by  chloride  of  barium.  Dry  the  precipitate,  and  treat  it 
as  directed  in  § 53.  If  the  precipitate  has  been  properly  washed  in  the 
manner  here  directed,  it  is  perfectly  pure,  and  gives  up  no  chloride  of 
barium  to  acetic  acid,  even  if  boiling,  nor  any  appreciable  trace  of  it  to 
boiling  nitric  acid,  though  the  solution  had  contained  that  salt.* 

b.  By  Evaporation. 

Add  to  the  solution,  in  a weighed  platinum  dish,  pure  sulphuric  acid 


* I mention  this  in  reference  to  Siegle’s  statement  in  the  Journal  f.  prakt. 
Chem.  G9,  142,  that  acetic  acid  and  nitric  acid  will  still  extract  small  quantities 
of  chloride  of  barium  from  sulphate  of  baryta,  formed  in  presence  of  an  excess 
of  sulphuric  acid,  and  thoroughly  washed  with  water. 


166 


DETERMINATION. 


[§  102. 


very  slightly  in  excess,  and  evaporate  on  the  water-bath  ; expel  the  excess 
of  sulphuric  acid  by  cautious  application  of  heat,  and  ignite  the  residue. 

For  the  properties  of  sulphate  of  baryta,  see  § 71. 

Both  methods,  if  properly  and  carefully  executed,  give  almost  absolutely 
accurate  results. 

2.  Determination  as  Carbonate  of  Daryta. 

a.  In  Solutions. 

Mix  the  moderately  dilute  solution  of  the  baryta  salt  in  a beaker 
with  ammonia,  add  carbonate  of  ammonia  in  slight  excess,  and  let 
the  mixture  stand  several  hours  in  a warm  place.  Filter,  wash  the 
precipitate  with  water  mixed  with  a little  ammonia,  dry,  and  ignite 
(§  53). 

For  the  properties  of  the  precipitate,  see  § 71.  This  method  in- 
volves a trifling  loss  of  substance,  as  the  carbonate  of  baryta  is  not  ab- 
solutely insoluble  in  water.  The  direct  experiment.  No.  62,  gave  99*79 
instead  of  100. 

If  the  solution  contains  a notable  quantity  of  ammoniaeal  salts,  the 
loss  incurred  is  much  more  considerable,  since  the  presence  of  such  salts 
greatly  increases  the  solubility  of  the  carbonate  of  baryta. 

b.  In  Salts  of  Daryta  with  Organic  Acids. 

Heat  the  salt  slowly  in  a covered  platinum  crucible,  until  no  more 
fumes  are  evolved ; place  the  crucible  obliquely,  with  the  lid  leaning 
against  it,  and  ignite,  until  the  whole  of  the  carbon  is  consumed,  and 
the  residue  presents  a perfectly  white  appearance  : moisten  the  residue 
with  a concentrated  solution  of  carbonate  of  ammonia,  evaporate,  ignite 
gently,  and  weigh.  The  results  obtained  by  this  method  are  quite 
satisfactory.  A direct  experiment,  No.  63,  gave  99*61  instead  of  100. 
The  loss  of  substance  which  almost  invariably  attends  this  method  is 
owing  to  particles  of  the  salt  being  carried  away  with  the  fumes 
evolved  upon  ignition,  and  is  accordingly  the  less  considerable,  the 
more  slowly  and  gradually  the  heat  is  increased.  Omission  of  the 
moistening  of  the  residue  with  carbonate  of  ammonia  would  involve  a 
further  loss  of  substance,  as  the  ignition  of  carbonate  of  baryta  in  con- 
tact with  carbon  is  attended  with  formation  of  some  caustic  baryta,  car- 
bonic oxide  gas  being  evolved. 


§102. 

2.  Strontia. 

a.  Solution. 

See  the  preceding  paragraph  (§  101,  a. — Solution  of  baryta),  the 
directions  there  given  applying  equally  here. 

b.  Determination . 

Strontia  is  weighed  either  as  sulphate  or  as  carbonate  of  strontia 
(§  72).  Strontia  in  the  pure  state,  or  in  form  of  carbonate,  may  be  de- 
termined also  by  the  volumetric  (alkalimetric)  method.  Comp.  § 210. 
We  may  convert  into 


§ 102.] 


STRONTIA. 


167 


1.  Sulphate  of  Strontia. 

a.  By  Precipitation . 

All  compounds  of  strontia  without  exception. 

b.  By  Evaporation. 

All  salts  of  strontia  with  volatile  acids,  if  no  other  non-volatile  body 
is  present. 


2.  Carbonate  of  Strontia. 

a.  All  compounds  of  strontia  soluble  in  water. 

j3.  Salts  of  strontia  with  organic  acids. 

The  method  based  on  the  precipitation  of  strontia  with  sulphuric 
acid  yields  accurate  results  only  in  cases  where  the  fluid  from  which  the 
strontia  is  to  be  precipitated  may  be  mixed,  without  injury,  with  alco- 
hol. Where  this  cannot  be  done,  and  where  the  method  based  on  the 
evaporation  of  'the  solution  of  strontia  with  sulphuric  acid  is  equally 
inapplicable,  the  conversion  into  the  carbonate  ought  to  be  resorted  to 
in  preference,  if  admissible.  As  in  the  case  of  baryta,  so  here,  we  have 
to  be  on  our  guard  against  the  presence  of  substances  which  would  im- 
pede precipitation. 

1.  Determination  as  Sulphate  of  Strontia. 
a.  By  Precipitation. 

Mix  the  solution  of  the  salt  of  strontia  (which  must  not  be  too 
dilute,  nor  contain  much  free  hydrochloric  or  nitric  acid)  with  dilute 
sulphuric  acid  in  excess,  in  a beaker,  and  add  at  least  an  equal  volume 
of  alcohol ; let  the  mixture  stand  twelve  hours,  and  filter ; wash  the 
precipitate  with  dilute  spirit  of  wine,  dry  and  ignite  (§  53). 

If  the  circumstances  of  the  case  prevent  the  use  of  alcohol,  the  fluid 
must  be  precipitated  in  a tolerably  concentrated  state,  allowed  to  stand 
in  the  cold‘  for  at  least  twenty-four  hours,  filtered,  and  the  precipitate 
washed  with  cold  water,  until  the  last  rinsings  manifest  no  longer  an 
acid  reaction,  and  leave  no  perceptible  residue  upon  evaporation.  If 
traces  of  free  sulphuric  acid  remain  adhering  to  the  filter,  the  latter 
turns  black  on  drying,  and  crumbles  to  pieces ; too  protracted  washing 
of  the  precipitate,  on  the  other  hand,  tends  to  increase  the  loss  of  sub- 
stance. 

Care  must  be  taken  that  the  precipitate  be  thoroughly  dry,  before 
proceeding  to  ignite  it ; otherwise  it  will  be  apt  to  throw  off  fine  par- 
ticles during  the  latter  process.  The  filter,  which  is  to  be  burnt  apart 
from  the  precipitate,  must  be  as  clean  as  possible,  or  some  loss  of  sub- 
stance will  be  incurred ; as  may  be  clearly  seen  from  the  depth  of  the 
carmine  tint  of  the  flame  with  which  the  filter  burns  if  the  precipitate 
has  not  been  properly  removed. 

For  the  properties  of  the  precipitate,  see  § 72.  When  alcohol  is 
used  and  the  directions  given  are  properly  adhered  to,  the  results  are 
very  accurate  ; when  the  sulphate  of  strontia  is  precipitated  from  an 
aqueous  solution,  on  the  contrary,  a certain  amount  of  loss  is  unavoid- 
able, as  sulphate  of  strontia  is  not  absolutely  insoluble  in  water.  The 
direct  experiments,  No.  64,  gave  only  98T2  and  98*02  instead  of  100. 
However,  the  error  may  be  rectified,  by  calculating  the  amount  of  sul- 


168 


DETERMINATION. 


[§  103. 

phate  of  strontia  dissolved  in  the  filtrate  and  the  wash-water,  basing 
the  calculation  upon  the  known  degree  of  solubility  of  sulphate  of 
strontia  in  pure  and  acidified  water.  See  Expt.  No.  65,  which,  with 
this  correction,  gave  99*77  instead  of  100. 

b.  JBy  Evaporation. 

The  same  method  as  described  for  baryta,  § 101,  1,  b. 

2.  Determination  as  Carbonate  of  Strontia. 

a.  In  Solutions. 

The  same  method  sis  described  § 101,  2,  a.  For  the  properties  of  the 
precipitate,  see  § 72.  The  method  gives  very  accurate  results,  as  car- 
bonate of  strontia  is  nearly  absolutely  insoluble  in  water  containing 
ammonia  and  carbonate  of  ammonia.  A direct  experiment,  No.  66, 
gave  99*82  instead  of  100.  Presence  of  ammoniacal  salts  exercises 
here  a less  adverse  influence  than  the  precipitation  of  carbonate  of 
baryta. 

b.  In  Salts  with  Organic  Acids. 

The  same  method  as  described  § 101,  2,  b.  The  remarks  made  there, 
respecting  the  accuracy  of  the  results,  apply  equally  here. 


§ 103. 

3.  Lime. 

a.  Solution. 

See  § 101,  a. — Solution  of  baryta.  Fluoride  of  calcium  is,  by  means 
of  sulphuric  acid,  converted  into  sulphate  of  lime,  and  the  latter  again, 
if  necessary,  decomposed  by  boiling  or  fusing  with  an  alkaline  carbon- 
ate (§  132).  [Sulphate  of  lime  dissolves  readily  in  moderately  dilute 
hydrochloric  acid.  It  is  much  less  soluble  in  strong  hydrochloric 
acid.] 

b.  Determination. 

Lime  is  weighed  either  as  sulphate,  or  as  carbonate  of  lime  (§  73).  It 
may  be  brought  into  the  first  form  by  evaporation,  or  by  precipitation; 
into  the  latter,  by  precipitation  as  oxalate,  or  at  once  as  carbonate,  or  by 
ignition. 

Small  quantities  of  lime  are  also  occasionally  reduced  to  the  caustic 
state,  instead  of  being  converted  into  carbonate.  Lime  in  the  pure  state, 
or  in  form  of  carbonate,  may  be  determined  also  by  the  volumetric 
(alkalimetric)  method.  Comp.  § 210. 

We  may  convert  into 

1.  Sulphate  of  Lime. 

a.  Dy  Precipitation. 

All  salts  of  lime  with  acids  soluble  in  alcohol,  provided  no  other  sub- 
stance insoluble  in  alcohol  be  present. 


§ 103.] 


LIME. 


169 


b.  By  Evaporation. 

All  salts  of  lime  with  volatile  acids,  provided  no  non-volatile  body  be 
present. 


2.  Carbonate  of  Lime. 

a.  By  Precipitation  with  Carbonate  of  Ammonia. 

All  salts  of  lime  soluble  in  water. 

b.  By  Precipitation  with  Oxalate  of  Ammonia. 

All  salts  of  lime  soluble  in  water  or  in  hydrochloric  acid  without 
exception. 

c.  By  Ignition. 

Salts  of  lime  with  organic  acids. 

Of  these  several  methods,  2,  b (precipitation  with  oxalate  of  ammonia) 
is  the  one  most  frequently  resorted  to.  This,  and  the  method  1,  b , give 
the  most  accurate  results.  The  method,  1,  a,  is  usually  resorted  to  only 
to  effect  the  separation  of  lime  from  other  bases ; 2,  generally  only  to 
effect  the  separation  of  lime  together  with  other  alkaline  earths  from  the 
alkalies.  As  many  bodies  (alkaline  citrates,  and  metaphosphates)  inter- 
fere with  the  precipitation  of  lime  by  the  precipitants  given,  these,  if  pre- 
sent, must  be  first  removed. 

1.  Determination  as  Sulphate  of  Lime . 

a.  By  Precipitation. 

Mix  the  solution  of  lime  in  a beaker,  with  dilute  sulphuric  acid  in 
excess,  and  add  twice  the  volume  of  alcohol ; let  the  mixture  stand  twelve 
hours,  filter,  and  thoroughly  wash  the  precipitate  with  spirit  of  wine,  dry, 
and  ignite  moderately  (§  53).  Tor  the  properties  of  the  precipitate,  see 
§73.  The  results  are  very  accurate.  A direct  experiment,  No.  67,  gave 
99*64  instead  of  100. 

b.  By  Evaporation. 

The  same  method  as  described  § 101,  1,  b. 

2.  Determination  as  Carbonate  of  Lime. 

a.  . By  Precipitation  with  Carbonate  of  Ammonia. 

The  same  method  as  described  § 101,  2,  a.  The  precipitate  must  be 
exposed  only  to  a very  gentle  red  heat,  but  this  must  be  continued  for 
some  time.  For  the  properties  of  the  precipitate,  see  § 73. 

This  method  gives  very  accurate  results,  the  loss  of  substance  incurred 
being  hardly  worth  mentioning. 

If  the  solution  contains  chloride  of  ammonium  or  similar  ammoniacal 
salts  in  considerable  proportion,  the  loss  of  substance  incurred  is  far 
greater.  The  same  is  the  case  if  the  precipitate  is  washed  with  pure  in- 
stead of  ammoniacal  water.  A direct  experiment,  No.  68,  in  which  pure 
water  was  used,  gave  99*17  instead  of  100  parts  of  lime. 


170 


DETERMINATION. 


[§  103. 


b.  By  Precipitation  with  Oxalate  of  Ammonia. 

a.  The  Lime  Salt  is  soluble  in  I Vater. 

To  the  hot  solution  in  a beaker,  add  oxalate  of  ammonia  in  moderate 
excess,  and  then  ammonia  sufficient  to  impart  an  ammoniacal  smell  to 
the  fluid ; cover  the  glass,  and  let  it  stand  in  a warm  place  until  the 
precipitate  has  completely  subsided,  which  will  require  twelve  hours, 
at  least.  Pour  the  clear  fluid  gently  and  cautiously,  so  as  to  leave  the 
precipitate  undisturbed,  on  a filter ; wash  the  precipitate  two  or  three 
times  by  decantation  with  hot  water;  lastly,  transfer  the  precipitate 
also  to  the  filter,  by  rinsing  with  hot  water,  taking  care,  before  the  ad- 
dition of  a fresh  portion,  to  wait  until  the  fluid  has  completely  passed 
through  the  filter.  Small  particles  of  the  precipitate,  adhering  firmly  to 
the  glass,  are  removed  with  a feather.  If  this  fails  to  effect  their  com- 
plete removal,  they  should  be  dissolved  in  a few  drops  of  highly  dilute 
hydrochloric  acid,  ammonia  added  to  the  solution,  and  the  oxalate  ob- 
tained added  to  the  first  precipitate.  Deviations  from  the  rules  laid 
down  here  will  generally  give  rise  to  the  passing  of  a turbid  fluid 
through  the  filter.  After  having  washed  the  precipitate,  dry  it  on  the 
filter  in  the  funnel,  and  transfer  the  dry  precipitate  to  a platinum  cru- 
cible, taking  care  to  remove  it  as  completely  as  possible  from  the  filter  ; 
burn  the  filter  on  a piece  of  platinum  wire,  letting  the  ash  drop  into  the 
hollow  of  the  lid  ; put  the  latter,  now  inverted,  on  the  crucible,  so  that 
the  filter  ash  may  not  mix  with  the  precipitate  ; heat  at  first  very  gently, 
then  more  strongly,  until  the  bottom  of  the  crucible  is  heated  to  very 
faint  redness.  Keep  it  at  that  temperature  from  ten  to  fifteen  minutes, 
removing  the  lid  from  time  to  time.  I am  accustomed  during  this  opera- 
tion to  move  the  lamp  backwards  and  forwards  under  the  crucible  with 
the  hand,  since,  if  you  allow  it  to  stand,  the  heat  may  very  easily  get 
too  high.  Finally  allow  to  cool  in  the  desiccator  and  weigh.  After 
weighing,  moisten  the  contents  of  the  crucible,  which  must  be  perfectly 
white,  or  barely  show  the  least  tinge  of  gray,  with  a little  water,  and 
test  this  after  a time  with  a minute  slip  of  turmeric  paper.  Should  the 
paper  turn  brown — a sign  that  the  heat  applied  was  too  strong — rinse 
off  the  fluid  adhering  to  the  paper  with  a little  water  into  the  crucible, 
throw  in  a small  lump  of  pure  carbonate  of  ammonia,  evaporate  to  dry- 
ness (best  in  the  water-bath),  heat  to  very  faint  redness,  and  weigh 
the  residue.  If  the  weight  has  increased,  repeat  the  same  operation  un- 
til the  weight  remains  constant.  This  method  gives  nearly  absolutely 
accurate  results;  and  if  the  application  of  heat  is  properly  managed, 
there  is  no  need  of  the  tedious  evaporation  with  carbonate  of  ammonia. 
A direct  experiment,  No.  69,  gave  99*99  instead  of  100. 

For  the  properties  of  the  precipitate  and  residue,  see  § 73. 

If  the  quantity  of  oxalate  of  lime  obtained  is  only  very  trifling,  I pre 
fer  to  convert  it  into  caustic  lime  or  into  the  sulphate.  To  effect  the 
former,  the  oxalate  of  lime  is  heated  to  intense  redness,  in  a small  plati- 
num crucible,  over  a gas  blow-pipe  flame  for  some  time.  The  conver- 
sion of  the  oxalate  into  sulphate  is  effected  most  conveniently  by  Schrot- 
ter’s  method,  viz.,  ignition  with  pure  sulphate  of  ammonia. 

Many  chemists  prefer  collecting  the  oxalate  of  lime  upon  a weighed 
filter,  and  drying  at  100°.  Thus  obtained  it  consists  of  2 Ca  O,  C406  + 2 
aq.  This  method,  besides  being  more  tedious,  gives  less  accurate  results 


MAGNESIA. 


171 


§ 104.] 


I 


than  that  based  on  the  conversion  of  the  oxalate  into  the  carbonate. 
The  direct  experiment,  No.  70,  gave  100*45  instead  of  100. 

Instead  of  weighing  the  oxalate  of  lime  as  such,  or  in  form  of  carbon- 
ate, &c.,  the  quantity  of  lime  present  in  the  salt  may  be  determined  also 
by  two  different  volumetric  methods. 

a.  Ignite  the  oxalate,  converting  it  thus  into  a mixture  of  carbonate 
and  caustic  lime,  and  determine  the  quantity  of  the  lime  by  the  alkalimet- 
ric  method  described  in  § 210  ; or, 

b.  Determine  the  oxalic  acid  in  the  well-washed  but  still  moist  oxalate 
of  lime  by  means  of  permanganate  of  potassa  (§  137),  and  reckon  for 
each  equivalent  of  bibasic  oxalic  acid  2 equivalents  of  lime  (Hempel). 

With  proper  care,  both  these  volumetric  methods  give  as  accurate 
results  as  those  obtained  by  weighing.  (Comp.  Expt.  No.  71.)  They 
deserve  to  be  recommended  more  particularly  in  cases  where  an  entire 
series  of  quantitative  estimations  of  lime  has  to  be  made.  TJnder  certain 
circumstances  it  may  also  prove  advantageous  to  precipitate  the  lime 
with  a measured  quantity  of  a standard  solution  of  oxalic  acid  or  qua- 
droxalate  of  potassa,  filter,  and  determine  the  excess  of  oxalic  acid  in 
the  filtrate.  (Kraut.*) 

(3.  The  Salt  is  insoluble  in  Water. 

Dissolve  the  salt  in  dilute  hydrochloric  acid.  If  the  acid  combined 
with  the  lime  is  of  a nature  to  escape  in  this  operation  ( e.g .,  carbonic 
acid),  or  to  admit  of  its  separation  by  evaporation  ( e.g .,  silicic  acid), 
proceed,  after  the  removal  of  the  acid,  as  directed  in  a.  But  if  the  acid 
cannot  thus  be  readily  got  rid  of  ( e.g .,  phosphoric  acid),  proceed  as  fol- 
lows: add  ammonia  until  a precipitate  begins  to  form,  re-dissolve  this 
with  a drop  of  hydrochloric  acid,  add  oxalate  of  ammonia  in  excess,  and 
finally  acetate  of  soda ; allow  the  precipitate  to  subside,  and  proceed  for 
the  renfainder  of  the  operation  as  directed  in  a.  In  this  process  the  free 
hydrochloric  acid  present  combines  with  the  ammonia  and  soda  of  the 
oxalate  and  acetate,  liberating  a corresponding  quantity  of  oxalic  acid  and 
acetic  acid,  in  which  acids  oxalate  of  lime  is  nearly  insoluble.  The 
method  yields  accurate  results.  A direct  experiment,  No.  72,  gave 
99*78  instead  of  100. 


c.  By  Ignition. 

The  same  method  as  described  § 101,  2,  b (baryta).  The  residue  re- 
maining upon  evaporation  with  carbonate  of  ammonia  (which  operation 
it  is  advisable  to  perform  twice)  must  be  ignited  very  gently.  The 
remarks  made  in  § 101,  2,  6,  in  reference  to  the  accuracy  of  the  results, 
apply  equally  here.  By  way  of  control,  the  carbonate  of  lime  may  be 
converted  into  the  caustic  state  or  into  sulphate  of  lime  (see  6,  a),  or  it 
may  be  determined  alkalimetrically  (§  210). 


\ 

§104. 


4.  Magnesia. 


a.  Solution. 

Many  of  the  compounds  of  magnesia  are  soluble  in  water;  those 


* Chem.  Centralblatt,  1856,  316. 


DETERMINATION. 


172 


[§  104. 


which  are  insoluble  in  that  menstruum  dissolve  in  hydrochloric  acid, 
with  the  exception  of  some  silicates  and  aluminates. 


b.  Determination. 

Magnesia  is  weighed  (§  74)  either  as  sulphate  or  as  pyrophosphate,  or 
as  pure  magnesia.  In  the  pure  state,  or  in  form  of  carbonate,  it  may  be 
determined  also  by  the  alkalimetric  method  described  in  § 210. 

We  may  convert  into 

1.  Sulphate  of  Magnesia. 


a.  Directly. 

All  compounds  of  magnesia  with 
volatile  acids,  provided  no  other  non- 
volatile substance  be  present. 


b.  Indirectly. 

All  compounds  of  magnesia  so- 
luble in  water,  and  also  those 
which,  insoluble  in  that  men- 
struum, dissolve  in  hydrochloric 
acid,  with  separation  of  their 
acid  (provided  no  ammoniacal 
salts  be  present). 


2.  Pyrophosphate  of  Magnesia. 


All  compounds  of  magnesia  without  exception. 

3.  Pure  Magnesia. 

a.  Salts  of  magnesia  with  organic  acids,  or  with  readily  volatile  in- 
organic oxygen  acids. 

b.  Chloride  of  magnesium,  and  the  compounds  of  magnesia  converti- 
ble into  that  salt. 

The  direct  determination  as  sulphate  of  magnesia  is  highly  recom- 
mended in  all  cases  where  it  is  applicable.  The  indirect  conversion  into 
the  sulphate  serves  only  in  the  case  of  certain  separations,  and  is  hardly 
ever  had  recourse  to  where  it  can  possibly  be  avoided.  The  deter- 
mination as  pyrophosphate  is  most  generally  resorted  to ; especially  also 
in  the  separation  of  magnesia  from  other  bases.  The  method  based  on 
the  conversion  of  chloride  of  magnesium  into  pure  magnesia  is  usually 
resorted  to  only  to  effect  the  separation  of  magnesia  from  the  fixed  alka- 
lies. Compounds  of  magnesia  with  phosphoric  acid  are  analyzed  as 
§134  directs. 

1.  Determination  as  Sulphate  of  Magnesia. 

Add  to  the  solution  excess  of  pure  dilute  sulphuric  acid,  evaporate  to 
dryness,  in  a weighed  platinum  dish,  on  the  water-bath ; then  heat  at 
first  cautiously,  afterwards,  with  the  cover  on  more  strongly — here  it  is 
advisable  to  place  the  lamp  so  that  the  flame  may  play  obliquely  on  the 
cover  from  above — until  the  excess  of  sulphuric  acid  is  completely 
expelled  ; lastly,  ignite  gently  over  the  lamp  for  some  time ; allow  to 
cool,  and  weigh.  Should  no  fumes  of  hydrated  sulphuric  acid  escape 
upon  the  application  of  a strongish  heat,  this  may  be  looked  upon  as  a 
sure  sign  that  the  sulphuric  acid  has  not  been  added  in  sufficient  quan- 
tity, in  which  case,  after  allowing  to  cool,  a fresh  portion  of  sulphuric 
acid  is  added.  The  method  yields  very  accurate  results.  Care  must  be 
taken  not  to  use  a very  large  excess  of  sulphuric  acid.  The  residue  must 


MAGNESIA. 


173 


§ 104.] 

be  exposed  to  a moderate  red  heat  only,  and  weighed  rapidly.  For  the 
properties  of  the  residue,  see  § 74. 

2.  Determination  as  Pyrophosphate  of  Magnesia. 

The  solution  of  the  salt  of  magnesia  is  mixed,  in  a beaker,  with  chlo- 
ride of  ammonium,  and  ammonia  added  in  slight  excess.  Should  a pre- 
cipitate form  upon  the  addition  of  ammonia,  this  may  be  considered  a 
sign  that  a sufficient  amount  of  chloride  of  ammonium  has  not  been 
used ; a fresh  amount  of  that  salt  must  consequently  be  added,  sufficient 
to  effect  the  re-solution  of  the  precipitate  formed.  The  clear  fluid  is 
then  mixed  with  a solution  of  phosphate  of  soda  in  excess,  and  the  mix- 
ture stirred,  taking  care  to  avoid  touching  the  sides  of  the  beaker  with 
the  stirring-rod  ; otherwise  particles  of  the  precipitate  are  apt  to  adhere 
so  firmly  to  the  rubbed  parts  of  the  beaker,  that  it  will  be  found  difficult 
to  remove  them ; the  beaker  is  then  covered,  and  allowed  to  stand  at 
rest  for  twelve  hours,  without  warming ; after  that  time  the  fluid  is  fil- 
tered, and  the  precipitate  collected  on  the  filter,  the  last  particles  of  it 
being  rinsed  out  of  the  glass  with  a portion  of  the  filtrate,  with  the  aid 
of  a feather;  when  the  fluid  has  completely  passed  through,  the  precipi- 
tate is  washed  with  a mixture  of  3 parts  of  water,  and  1 part  of  solution 
of  ammonia  of  0*96  sp.  gr.,  the  operation  being  continued  until  a few 
drops  of  the  fluid  passing  through  the  filter  mixed  with  nitric  acid  and 
a drop  of  nitrate  of  silver  show  only  a very  slight  opalescence. 

The  precipitate  is  now  thoroughly  dried,  and  then  transferred  to  a 
platinum  crucible  (§  53)  ; the  latter,  with  the  lid  on,  is  exposed  for  some 
time  to  a very  gentle  heat,  which  is  finally  increased  to  intense  redness. 
The  filter,  as  clean  as  practicable,  is  incinerated  in  a spiral  of  platinum 
wire,  and  the  ash  transferred  to  the  crucible,  which  is  then  once  more 
exposed  to  a red  heat,  allowed  to  cool,  and  weighed. 

For  the  properties  of  the  precipitate  and  residue,  see  § 74. 

This  method,  if  properly  executed,  yields  most  accurate  results.  The 
precipitate  must  be  washed  completely,  but  not  over-washed,  and  the 
washing  water  must  always  contain  the  requisite  quantity  of  ammonia. 

Direct  experiments,  No.  73,  a and  b,  gave  respectively  100*43  and 
100*30  instead  of  100. 

3.  Determination  as  pure  Magnesia. 

a.  In  Salts  of  Magnesia  with  Organic  or  Volatile  Inorganic  Acids. 

The  salt  of  magnesia  is  gently  heated  in  a covered  platinum  crucible, 
increasing  the  temperature  gradually,  until  no  more  fumes  escape ; the 
lid  is  then  removed,  and  the  crucible  placed  in  an  oblique  position,  with 
the  lid  leaning  against  it.  A red  heat  is  now  applied,  until  the  residue 
is  perfectly  white.  For  the  properties  of  the  residue,  see  § 74.  The 
method  gives  the  more  accurate  results  the  more  slowly  the  salt  is  heated 
from  the  beginning.  Some  loss  of  substance  is  usually  sustained,  owing 
to  traces  of  the  salt  being  carried  off  with  the  empyreumatic  products. 
Salts  of  magnesia  with  readily  volatile  oxygen  acids  (carbonic  acid, 
nitric  acid),  may  be  transformed  into  magnesia  in  a similar  way,  by  sim- 
ple ignition.  Even  sulphate  of  magnesia  loses  the  whole  of  its  sulphuric 
acid  when  exposed,  in  a platinum  crucible,  to  the  heat  of  the  gas  blow- 
pipe-flame (Sonnenschein).  As  regards  small  quantities  of  sulphate  of 
magnesia,  I can  fully  confirm  this  statement. 


174 


DETERMINATION. 


b.  Conversion  of  Chloride  of  Magnesium  into  pure  Magnesia.  See  § 

153,  4,  y. 


THIRD  GROUP  OF  THE  BASES. 

ALUMINA — SESQUIOXIDE  OF  CHROMIUM — (TITANIC  ACID). 

§105. 

1.  Alumina. 

a.  Solution . 

Those  of  the  compounds  of  alumina  which  are  insoluble  in  water, 
dissolve,  for  the  most  part,  in  hydrochloric  acid.  Native  crystallized 
alumina  (sapphire,  ruby,  corundum,  &c.),  and  many  native  alumina  com- 
pounds, and  also  artificially  produced  alumina  after  intense  ignition, 
require  fusing  with  carbonate  of  soda,  caustic  potassa,  or  hydrate  of 
baryta,  as  a preliminary  step  to  their  solution  in  hydrochloric  acid. 
Many  alumina  compounds  which  resist  the  action  of  concentrated  hydro- 
chloric acid,  may  be  decomposed  by  protracted  heating  with  moderately 
concentrated  sulphuric  acid,  or  by  fusion  with  bisulphate  of  potassa; 
e.g.y  common  clay. 

b.  Determination. 

Alumina  is  invariably  weighed  in  th z pure  state  (§  75).  The  several 
compounds  of  alumina  are  converted  into  pure  alumina,  either  by  preci- 
pitation as  hydrate  of  alumina,  and  subsequent  ignition,  or  by  simple 
ignition.  Precipitation  as  basic  acetate  or  basic  formiate  is  resorted  to 
only  in  cases  of  separation. 

We  may  convert  into 

PURE  ALUMINA. 

a.  By  Precipitation.  b.  By  Heating  or  Ignition. 

All  compounds  of  alumina  solu-  a.  All  salts  of  alumina  with 
ble  in  water,  and  those  which,  in-  readily  volatile  acids  ( e.g .,  nitrate 
soluble  in  that  menstruum,  dis-  of  alumina). 

solve  in  hydrochloric  acid,  with  se-  j3.  All  salts  of  alumina  with  or- 
paration  of  their  acid.  ganic  acids. 

With  regard  to  the  method  a,  it  must  be  remembered  that  the  solu- 
tion must  contain  no  organic  substances,  which  would  interfere  with  the 
precipitation — e.g.,  tartaric  acid,  sugar,  &c.  Should  such  be  present,  the 
solution  must  be  mixed  with  carbonate  of  soda  and  nitrate  of  potassa, 
evaporated  to  dryness  in  a platinum  dish,  the  residue  fused,  then  soft- 
ened with  water,  transferred  to  a beaker,  digested  with  hydrochloric 
acid,  and  the  solution  filtered,  and  then,  but  not  before,  precipitated. 

The  methods  6,  a and  3,  are  applicable  only  in  cases  where  no  other 
fixed  substances  are  present.  The  methods  of  estimating  alumina 
in  its  combinations  with  phosphoric,  boracic,  silicic,  and  chromic  acids, 
will  be  found  in  Part  II.  of  this  Section,  under  the  heads  of  these 
several  acids. 


ALUMINA. 


175 


§ 105.] 

Determination  as  pure  Alumina. 

a.  JBy  Precipitation. 

Mix  the  moderately  dilute  hot  solution  of  alumina,  in  a beaker  or 
dish,  with  a tolerable  quantity  of  chloride  of  ammonium,  if  that  salt  is 
not  already  present ; add  ammonia  slightly  in  excess,  boil  gently  till 
the  steam  ceases  to  brown  turmeric  paper,  allow  to  settle  ; then  decant 
the  clear  supernatant  fluid  on  to  a filter,  taking  care  not  to  disturb  the 
precipitate  ; pour  boiling  water  on  the  latter  in  the  beaker,  stir,  let  the 
precipitate  subside,  decant  again,  and  repeat  this  operation  of  washing 
by  decantation  a second  and  a third  time  ; transfer  the  precipitate  now 
to  the  filter,  finish  the  washing  with  boiling  water,  dry  thoroughly, 
ignite  (§  52),  and  weigh.  The  heat  applied  should  be  very  gentle  at 
first,  and  the  crucible  kept  well  covered,  to  guard  against  the  risk  of  loss 
of  substance  from  spirting,  which  is  always  to  be  apprehended  if  the  pre- 
cipitate is  not  thoroughly  dry  ; towards  the  end  of  the  process  the  heat 
should  be  raised  to  intense  redness.  In  the  case  of  sulphate  of  alumina 
the  foregoing  process  is  apt  to  leave  some  sulphuric  acid  in  the  precipi- 
tate, which,  of  course,  vitiates  the  result.  To  insure  the  removal  of 
this  sulphuric  acid,  the  precipitate  should  be  exposed  for  5-10  min.  to 
the  heat  of  the  gas  blowpipe  flame.  If  there  are  difficulties  in  the  way, 
preventing  this  proceeding,  the  precipitate,  either  simply  washed  or  mo- 
derately ignited,  must  be  re-dissolved  in  hydrochloric  acid  (which  re- 
quires protracted  warming  with  strong  acid),  and  then  precipitated  again 
with  ammonia ; or  the  sulphate  must  first  be  converted  into  nitrate  by 
decomposing  it  with  nitrate  of  lead,  added  in  very  slight  excess,  the  ex- 
cess of  lead  removed  by  means  of  hydrosulphuric  acid,  and  the  further 
process  conducted  according  to  the  directions  of  a or  b.  For  the  pro- 
perties of  hydrate  of  alumina  and  ignited  alumina,  see  § 75.  The 
method,  if  properly  executed,  gives  very  accurate  results.  But  if  a con- 
siderable excess  of  ammonia  is  used,  more  particularly  in  the  absence  of 
ammoniacal  salts,  and  the  liquid  is  filtered  without  boiling  or  long 
standing  in  a warm  place  to  remove  the  ammonia,  no  trifling  loss  may 
be  incurred.  This  loss  is  the  greater,  the  more  dilute  the  solution,  and 
the  larger  the  excess  of  ammonia.  The  precipitate  cannot  well  be  suffici- 
ently washed  on  the  filter  on  account  of  its  gelatinous  nature ; on  the 
other  hand,  if  it  be  entirely  washed  by  decantation,  a very  large  quan- 
tity of  wash-water  must  be  used,  hence  it  is  advisable  to  combine  the 
two  methods,  as  directed.* 

b.  Py  Ignition. 

a.  Compounds  of  Alumina  with  Volatile  Acids. 

Ignite  the  salt  (or  the  residue  of  the  evaporated  solution)  in  a pla- 
tinum crucible,  gently  at  first,  then  gradually  to  the  very  highest  degree 
of  intensity,  until  the  weight  remains  constant.  For  the  properties  of 
the  residue,  see  § 75.  Its  purity  must  be  carefully  tested.  There  are 
no  sources  of  error. 


* [When  a solution  of  alumina  in  hydrate  of  potassa  or  hydrate  of  soda  is  boiled 
with  excess  of  chloride  of  ammonium,  the  alumina  separates  completely  as  a 
hydrate  with  two  eq.  of  water,  which  may  be  washed  with  comparative  ease. 
In  certain  cases,  as  where  alumina  is  separated  from  sesquioxide  of  iron  by 
hydrate  of  soda,  this  fact  may  be  taken  advantage  of.  Lowe,  Fres.  Zeitschriit. 
IV.  355.] 


176 


DETERMINATION. 


[§  106. 


f 3 . Compounds  of  Alumina  with  Organic  Acids . 
The  same  method  as  described  § 104,  3,  a (Magnesia). 


106. 


2.  Sesquioxide  of  Chromium. 


a.  Solution. 

Many  of  the  compounds  of  sesquioxide  of  chromium  are  soluble  in 
water.  The  hydrated  sesquioxide,  and  most  of  the  salts  insoluble  in 
water,  dissolve  in  hydrochloric  acid.  Ignition  renders  sesquioxide  of 
chromium  and  many  of  its  salts  insoluble  in  acids ; this  insoluble  modi- 
fication must  be  prepared,  for  solution  in  hydrochloric  acid,  by  fusing 
with  3 or  4 parts  of  potassa.  A small  quantity  is  converted,  in  the 
process  of  fusing,  into  chromic  acid,  by  the  action  of  the  air ; this  is, 
however,  reduced  again  to  sesquioxide  upon  heating  with  hydrochloric 
acid.  Addition  of  alcohol  greatly  promotes  the  reduction.  Instead  of 
this  fusing  with  potassa,  we  frequently  prefer  to  adopt  a treatment, 
whereby  the  sesquioxide  is  at  once  oxidized  and  converted  into  an 
alkaline  chromate  (see  2).  For  the  solution  of  chromic  iron,  see 
§ 160. 

b.  Determination. 

Sesquioxide  of  chromium  is  always,  when  directly  determined, 
weighed  in  the  pure  state.  It  is  brought  into  this  form  either  by  pre- 
cipitation as  hydrate  and  ignition,  or  by  simple  ignition.  It  may,  how- 
ever, also  be  estimated,  by  conversion  into  chromic  acid,  and  determi- 
nation as  such. 

We  may  convert  into 


1.  Pure  Sesquioxide  of  Chromium. 


a.  j By  Precipitation. 

All  compounds  of  sesquioxide 
of  chromium  soluble  in  water,  and 
also  those  which,  insoluble  in  that 
menstruum,  dissolve  in  hydrochlo- 
ric acid,  with  separation  of  their 
acid.  Provided  always  that  no 
organic  substances  (such  as  tartaric 
acid,  oxalic  acid,  &c.)  which  inter- 
fere with  the  precipitation  be  pre- 
sent. 


b.  Dy  Ignition. 

a.  All  salts  of  sesquioxide  of 
chromium  with  volatile  oxygen 
acids,  provided  no  non-volatile  sub- 
stances be  present. 

j3.  Salts  of  sesquioxide  of  chro- 
mium with  organic  acids. 


2.  Chromic  acid,  or,  more  correctly  speaking,  alkaline  chromate. 

Sesquioxide  of  chromium  and  all  its  salts. 

The  methods  of  analyzing  the  combinations  of  the  sesquioxide  of 
chromium  with  chromic  acid,  phosphoric  acid,  boracic  acid,  and  silicic 
acid,  will  be  found  in  Part  II.  of  this  Section,  under  the  heads  of  these 
several  acids. 


1.  Determination  as  Sesquioxide  of  Chromium . 
a.  Dy  Precipitation. 

The  solution,  which  must  not  be  too  highly  concentrated,  is  heated 


§ 106.]  SESQUIOXIDE  OF  CHROMIUM.  177 

to  100°  in  a beaker.  Ammonia  is  then  added  slightly  in  excess,  and 
the  mixture  exposed  to  a temperature  approaching  boiling,  until  the 
fluid  over  the  precipitate  is  perfectly  colorless,  presenting  no  longer  the 
least  shade  of  red  ; let  the  solid  particles  subside,  wash  three  times 
by  decantation,  and  lastly  on  the  filter,  with  hot  water,  dry  thoroughly, 
and  ignite  (§  52).  The  heat  in  the  latter  process  must  be  increased 
gradually,  and  the  crucible  kept  covered,  otherwise  some  loss  of  sub- 
stance is  likely  to  arise  from  spirting  upon  the  incandescence  of  the  ses- 
quioxide  of  chromium  which  marks  the  passing  of  the  soluble  into  the 
insoluble  modification.  For  the  properties  of  the  precipitate  and  resi- 
due, see  § 76.  This  method,  if  properly  executed,  gives  very  accurate 
results. 

b.  JBy  Ignition. 

a.  Salts  of  Sesquioxide  of  Chromium  with  Volatile  Acids. 

The  same  method  as  described,  § 105,  b , a (Alumina). 

b.  Salts  of  Sesquioxide  of  Chromium  with  Organic  Acids. 

The  same  method  as  described  § 104,  3,  a (Magnesia). 

2.  Conversion  of  Sesquioxide  of  Chromium  into  Chromic  Acid. 

(For  the  estimation  of  chromic  acid,  see  § 130.) 

The  following  methods  have  been  proposed  with  this  view : — 

a.  The  solution  of  the  salt  of  sesquioxide  of  chromium  is  mixed 
with  solution  of  potassa  or  soda  in  excess,  until  the  hydrated  sesquioxide, 
which  forms  at  first,  is  redissolved.  Chlorine  gas  is  then  conducted 
into  the  cold  fluid  until  it  acquires  a yellowish-red  tint;  it  is  then 
mixed  with  potassa  or  soda  in  excess,  and  the  mixture  evaporated  to 
dryness ; the  residue  is  ignited  in  a platinum  crucible.  The  whole  of 
the  chlorate  of  potassa  (or  soda)  formed  is  decomposed  by  this  process, 
and  the  residue  consists,  therefore,  now  of  an  alkaline  chromate  and 
chloride  of  potassium  (or  sodium). — (Yohl.) 

b.  Hydrate  of  potassa  is  heated  in  a silver  crucible  to  calm  fusion  ; 
the  heat  is  then  somewhat  moderated,  and  the  perfectly  dry  com- 
pound of  sesquioxide  of  chromium  projected  into  the  crucible.  When 
the  sesquioxide  of  chromium  is  thoroughly  moistened  with  the  potassa, 
small  lumps  of  fused  chlorate  of  potassa  are  added.  A lively  efferve- 
scence ensues,  from  the  escape  of  oxygen ; at  the  same  time  the  mass 
acquires  a more  and  more  yellow  color,  and  finally  becomes  clear  and 
transparent.  Loss  of  substance  must  be  carefully  guarded  against  (H. 
Schwarz). 

c.  Dissolve  the  sesquioxide  of  chromium  in  solution  of  potassa  or 
soda,  add  binoxide  of  lead  in  sufficient  excess,  and  warm.  The  yellow 
fluid  produced  contains  all  the  chromium  as  chromate  of  lead  in  alka- 
line solution.  Filter  from  the  excess  of  binoxide  of  lead,  add  to  the  filtrate 
acetic  acid  to  acid  reaction,  and  determine  the  weight  of  the  precipi- 
tated chromate  of  lead  (G.  Chancel  *). 

\d.  Render  the  solution  of  sesquioxide  of  chromium  nearly  neutral 
by  a solution  of  carbonate  of  soda,  add  acetate  of  soda  in  excess,  heat 
and  add  chlorine  water,  or  pass  in  chlorine  gas,  keeping  the  solution 
nearly  neutral  by  occasional  addition  of  carbonate  of  soda.  The  oxida- 


12 


* Comp.  rend.  43,  937. 


178 


DETERMINATION. 


tion  proceeds  readily.  Boil  off  excess  of  chlorine,  when  the  chromic 
acid  may  be  precipitated  as  chromate  of  lead  or  chromate  of  baryta 
(W.  Gibbs*).] 


§ 107. 


Supplement  to  the  Third  Group. 
Titanic  Acid. 


Titanic  acid  is  always  weighed  in  the  pure  state  ; its  separation  is 
effected  either  by  precipitation  with  an  alkali  or  by  boiling  its  dilute 
acid  solution.  In  precipitating  acid  solutions  of  titanic  acid  ammonia 
is  employed  ; take  care  to  add  the  precipitating  agent  only  in  slight 
excess,  let  the  precipitate  formed,  which  resembles  hydrate  of  alumina, 
deposit,  wash,  first  by  decantation,  then  completely  on  the  filter,  dry, 
and  ignite  (§52).  If  the  solution  contained  sulphuric  acid,  put  some 
carbonate  of  ammonia  into  the  crucible,  after  the  first  ignition,  to  se- 
cure the  removal  of  every  remaining  trace  of  that  acid.  Lose  no  time 
in  weighing  the  ignited  titanic  acid,  as  it  is  slightly  hygroscopic.  If  we 
have  titanic  acid  dissolved  in  sulphuric  acid,  as  for  instance  occurs 
when  we  fuse  it  with  bisulphate  of  potassa  and  treat  the  mass  with 
cold  water,  we  may,  by  largely  diluting,  and  long  boiling,  with  renewal 
of  the  evaporating  water,  fully  precipitate  the  titanic  acid.  Thus 
separated,  it  is  easy  to  wash.  In  the  process  of  igniting  the  dried  pre- 
cipitate, some  carbonate  of  ammonia  is  added.  From  dilute  hydro- 
chloric acid  solutions  of  titanic  acid,  the  latter  separates  completely 
only  upon  evaporating  the  fluid  to  dryness ; and  if  the  precipitate  in 
that  case  were  washed  with  pure  water,  the  filtrate  would  be  milky  ; 
acid  must,  therefore,  be  added  to  the  water. 

Hydrate  of  titanic  acid  precipitated  in  the  cold,  washed  with  cold 
water,  and  dried  without  elevation  of  temperature,  is  completely  solu- 
ble in  hydrochloric  acid  ; otherwise  it  dissolves  only  incompletely  in 
that  acid.  Titanic  acid  thrown  down  from  dilute  acid  solutions  by 
boiling,  is  not  soluble  in  dilute  acids.  Ignited  titanic  acid  does  not  dis- 
solve even  in  concentrated  hydrochloric  acid,  but  it  does  dissolve  by  long 
heating  with  tolerably  concentrated  sulphuric  acid.  The  easiest  way 
of  effecting  its  solution  is  to  fuse  it  for  some  time  with  bisulphate  of 
potassa,  and  treat  the  fused  mass  with  a large  quantity  of  cold  water. 
Upon  fusing  with  carbonate  of  soda,  titanate  of  soda  is  formed,  which, 
when  treated  with  water,  leaves  acid  titanate  of  soda,  which  is  soluble 
in  hydrochloric  acid.  Titanic  acid  (Ti  02)  consists  of  60*98  per  cent,  of 
titanium,  and  39*02  per  cent,  of  oxygen. 


FOURTH  GROUP  OF  THE  BASES. 

Oxide  of  Zinc — Protoxide  of  Manganese — Protoxide  of  Nickel — 
Protoxide  of  Cobalt — Protoxide  of  Iron — Sesquioxide  of  Iron — 
(Sesquioxide  of  Uranium). 


* [Am.  Joum.  Sci.  2 Ser.  39,  58.] 


§ 108.] 


OXIDE  OF  ZINC. 


179 


§ 108. 

1.  Oxide  of  Zinc. 

a.  Solution. 

Many  of  the  salts  of  zinc  are  soluble  in  water.  Metallic  zinc,  oxide  of 
zinc,  and  the  salts,  which  are  insoluble  in  water,  dissolve  in  hydrochloric 
acid.  To  dissolve  sulphide  of  zinc  it  is  best  to  employ  nitric  acid  or  aqua 
regia. 

b.  Determination. 

Zinc  is  weighed  either  as  oxide  or  as  sulphide  (§  77).  The  conversion 
of  the  salts  of  zinc  into  the  oxide  is  effected  either  by  precipitation  as 
basic  carbonate  or  sulphide  of  zinc,  or  by  direct  ignition.  Besides  these 
gravimetric  methods,  several  volumetric  methods  are  in  use. 

We  may  convert  into 

1.  Oxide  of  Zinc. 

a.  By  Precipitation  as  Carbonate 
of  Zinc. 

All  the  salts  of  zinc  which  are 
soluble  in  water,  and  all  those  with 
organic  volatile  acids ; also  those 
salts  of  zinc  which,  insoluble  in 
water,  dissolve  in  hydrochloric  acid, 
with  separation  of  their  acid, 

c.  By  direct  Ignition. 

Salts  of  zinc  with  volatile  inorganic  oxygen  acids. 

2,  Sulphide  of  Zinc. 

All  compounds  of  zinc  without  exception. 

The  method  1,  c,  is  to  be  recommended  only,  as  regards  the  more  fre- 
quently occurring  compounds  of  zinc,  for  the  carbonate  and  the  nitrate. 
The  methods  1,  b,  or  2,  are  usually  only  resorted  to  in  cases  where  1,  a, 
is  inadmissible.  They  serve  more  especially  to  separate  oxide  of  zinc 
from  other  bases.  Salts  of  zinc  with  organic  acids  cannot  be  converted 
into -the  oxide  by  ignition,  since  this  process  would  cause  the  reduction 
and  volatilization  of  a small  portion  of  the  metal.  If  the  acids  are  volatile, 
the  zinc  may  be  determined  at  once,  according  to  method  1,  a : if,  on  the 
contrary,  the  acids  are  non-volatile,  the  zinc  is  best  precipitated  as  sul- 
phide. For  the  analysis  of  chromate,  phosphate,  borate,  and  silicate  of 
zinc,  look  to  the  several  acids.  The  volumetric  methods  are  chiefly  em- 
ployed for  technical  purposes  ; see  Special  Part. 

1.  Determination  as  Oxide  of  Zinc. 

a.  By  Precipitation  as  Carbonate  of  Zinc. 

Heat  the  moderately  dilute  solution  nearly  to  boiling  in  a capacious 
vessel,  best  in  a platinum  dish  ; add,  drop  by  drop,  carbonate  of  soda  in 
excess ; boil  a few  minutes ; allow  to  subside,  decant  through  a filter,  and 
boil  the  precipitate  three  times  with  water,  decanting  each  time ; then 


b.  By  Precipitation  as  Sulphide 
of  Zinc. 

All  compounds  of  zinc  without 
exception. 


180 


DETERMINATION. 


transfer  the  precipitate  to  the  filter,  wash  completely  with  hot  water,  dry, 
and  ignite  as  directed  § 53,  taking  care  to  have  the  filter  as  clean  as  prac- 
ticable, before  proceeding  to  incinerate  it.  Should  the  solution  contain 
ammoniacal  salts,  the  ebullition  must  be  continued  until,  upon  a fresh  addi- 
tion of  the  carbonate  of  soda,  the  escaping  vapor  no  longer  imparts  a brown 
tint  to  turmeric  paper.  If  the  quantity  of  ammoniacal  salts  present  is  con- 
siderable, the  fluid  must  be  evaporated  boiling  to  dryness.  It  is,  therefore, 
in  such  cases  more  convenient  to  precipitate  the  zinc  as  sulphide  (see  b). 

The  presence  of  a great  excess  of  acid  in  the  solution  of  zinc  must  be  as 
much  as  possible  guarded  against,  that  the  effervescence  from  the  escaping 
carbonic  acid  gas  may  not  be  too  impetuous.  The  filtrate  must  always  be 
tested  with  sulphide  (with  addition  of  chloride)  of  ammonium  to  ascertain 
whether  the  whole  of  the  zinc  has  been  precipitated  ; a slight  precipitate 
will  indeed  invariably  form  upon  the  application  of  this  test ; but,  if  the 
process  has  been  properly  conducted,  this  is  so  insignificant  that  it  may  be 
altogether  disregarded,  being  limited  to  some  exceedingly  slight  and  im- 
ponderable flakes,  which  moreover  make  their  appearance  only  after  many 
hours’  standing.  If  the  precipitate  is  more  considerable,  however,  it  must 
be  treated  as  directed  in  b , and  the  weight  of  the  oxide  of  zinc  obtained 
added  to  that  resulting  from  the  first  process.  For  the  properties  of  the 
precipitate  and  residue,  see  § 77.  This  method  yields  pretty  accurate 
results,  though  they  are  in  most  cases  a little  too  low,  as  the  precipitation 
is  never  absolutely  complete,  and  as  particles  of  the  precipitate  will  always 
and  unavoidably  adhere  to  the  filter,  which  exposes  them  to  the  chance  of 
reduction  and  volatilization  during  the  process  of  ignition.  On  the  other 
hand,  the  results  are  sometimes  too  high  ; this  is  owing  to  defective  washing, 
as  may  be  seen  from  the  alkaline  reaction  which  the  residue  manifests  in  such 
cases.  It  is  advisable  also  to  ascertain  whether  the  residue  will  dissolve  in 
hydrochloric  acid  without  leaving  silicic  acid  ; this  latter  precaution  is  in- 
dispensable in  cases  where  the  precipitation  has  been  effected  in  a glass  vessel. 

[It  is  often  better,  especially  in  presence  of  ammonia  salts,  to  heat  the 
dry  zinc  salt  with  excess  of  carbonate  of  soda  in  a platinum  dish  cau- 
tiously to  near  redness,  then  treat  with  hot  water  and  wash  as  directed.] 

b.  By  Precipitation  as  Sulphide  of  Zinc. 

Mix  the  solution,  contained  in  a not  too  large  flask  and  sufficiently 
diluted,  with  chloride  of  ammonium,  then  add  ammonia,  till  the  reaction 
is  j ust  alkaline,  and  then  colorless  or  slightly  yellow  sulphide  of  ammo- 
nium in  moderate  excess.  If  the  flask  is  not  now  quite  full  up  to  the  neck, 
make  it  so  with  water,  cork,  allow  to  stand  12  to  24  hours  in  a warm 
place,  wash  the  precipitate,  if  considerable,  first  by  decantation,  then  on 
the  filter  with  water  containing  sulphide  of  ammonium  and  also  less  and 
less  chloride  of  ammonium  (finally  none).  In  decanting  do  not  pour  the 
fluid  through  the  filter,  but  at  once  into  a flask.  After  thrice  decanting, 
filter  the  fluid  that  was  poured  off,  and  then  transfer  the  precipitate  to  the 
filter,  finishing  the  washing  as  directed.  The  funnel  is  kept  covered  with 
a glass  plate.  If  the  zinc  is  not  to  be  determined  according  to  2,  then 
put  the  moist  filter  with  the  precipitate  in  a beaker,  and  pour  over  it 
moderately  dilute  hydrochloric  acid  slightly  in  excess.  Put  the  glass 
now  in  a warm  place,  until  the  solution  smells  no  longer  of  sulphuretted 
hydrogen ; dilute  the  fluid  with  a little  water,  filter,  wash  the  original 
filter  with  hot  water,  and  proceed  with  the  solution  of  chloride  of  zinc 
obtained  as  directed  in  a. 


108.] 


OXIDE  OF  ZINC. 


181 


From  a solution  of  acetate  of  zinc  the  metal  may  be  precipitated  com- 
pletely, or  nearly  so,  with  sulphuretted  hydrogen  gas,  even  in  presence  of 
an  excess  of  acetic  acid,  provided  always  no  other  acid  be  present  (Expt. 
No.  74).  The  precipitated  sulphide  of  zinc  is  washed  with  water  impreg- 
nated with  sulphuretted  hydrogen,  and,  for  the  rest,  treated  exactly  like 
the  sulphide  of  zinc  obtained  by  precipitation  with  sulphide  of  ammonium. 

Small  quantities  of  sulphide  of  zinc  may  also  be  converted  directly  in- 
to the  oxide,  by  heating  in  an  open  platinum  crucible,  to  gentle  redness 
at  first,  then,  after  some  time,  to  most  intense  redness. 

c.  JBy  direct  Ignition . 

The  salt  is  exposed,  in  a covered  platinum  crucible,  first  to  a gentle 
heat,  finally  to  a most  intense  heat,  until  the  weight  of  the  residue 
remains  constant.  The  action  of  reducing  gases  is  to  be  avoided. 

2.  Determination  as  Sulphide  of  Zinc. 

The  precipitated  sulphide  of  zinc,  obtained  as  in  1,  b , maybe  ignited 
in  hydrogen  and  weighed.  H.  Kose,*  who  has  lately  recommended 
the  process,  employs  the  following  apparatus. 


Fig.  47. 


a contains  concentrated  sulphuric  acid,  b,  chloride  of  calcium.  The 
porcelain  crucible  has  a perforated  porcelain  or  platinum  cover,  into  the 
opening  of  which  fits  the  porcelain  or  platinum  tube,  d.  The  latter  is 
provided  with  an  annular  projection  which  rests  on  the  cover,  the  tube 
itself  extends  some  distance  into  the  crucible.  When  the  sulphide  of 
zinc  has  dried  in  the  filter,  it  is  transferred  to  the  weighed  porcelain 
crucible,  the  filter  ashes  added,  powdered  sulphur  is  sprinkled  over  the 
contents  of  the  crucible,  the  cover  is  placed  on,  and  hydrogen  is  passed  in 
a moderate  stream,  a gentle  heat  is  applied  at  first,  which  is  after- 
wards raised  for  five  minutes  to  intense  redness ; finally  the  crucible  is 


Pogg.  Anal.  110,  128. 


DETERMINATE  ON. 


182 


[§  109. 


allowed  to  cool  with  continued  transmission  of  the  gas,  and  the  sulphide 
of  zinc  is  weighed. 

[Instead  of  the  porcelain  tube  and  perforated  cover,  a common 
tobacco-pipe  may  be  employed,  the  bowl  of  the  latter  being  inverted 
over  or  within  a porcelain  crucible.  Sulphuretted  hydrogen  may  be 
advantageously  substituted  for  hydrogen.] 

Oesten’s  experiments,  which  were  adduced  by  Rose  in  support  of  the 
accuracy  of  this  method,  were  highly  satisfactory. 

Sulphate,  carbonate,  and  oxide  of  zinc  may  be  converted  into  sulphide 
in  the  manner  just  described.  They  must,  however,  be  mixed  with  an 
excess  of  powdered  sulphur,  otherwise  you  will  lose  some  zinc  from  the 
reducing  action  of  the  hydrogen  (H.  Rose). 


§ 109. 

2.  Protoxide  of  Manganese. 

a.  Solution. 

Many  of  the  salts  of  protoxide  of  manganese  are  soluble  in  water.  The 
pure  protoxide,  and  those  of  its  salts  which  are  insoluble  in  that  men- 
struum, dissolve  in  hydrochloric  acid,  which  dissolves  also  the  higher 
oxides  of  manganese.  The  solution  of  the  higher  oxides  is  attended  with 
evolution  of  chlorine — equivalent  in  quantity  to  the  amount  of  oxygen 
which  the  oxide  under  examination  contains,  more  than  the  protoxide 
of  manganese — and  the  fluid,  after  application  of  heat,  is  found  to  con- 
tain protochloride  of  manganese. 

b.  Determination. 

Manganese  is  weighed  either  as  protosesquioxide,  as  sulphide , or  as 
pyrophosphate  (§  78.)  Into  the  form  of  protosesquioxide  it  is  con- 
verted either  by  precipitation  as  carbonate  of  protoxide,  or  as  hydrated 
protoxide,  sometimes  preceded  by  precipitation  as  sulphide  of  -manga- 
nese, or  as  binoxide  of  manganese ; or,  finally,  by  direct  ignition. 
[When  estimated  as  pyrophosphate  it  is  precipitated  as  ammonio-phos- 
phate.] 

Manganese  may  be  determined  volumetrically  in  two  different  ways, 
one  being  applicable  to  any  solution  of  protoxide  of  manganese,  provided 
it  be  free  from  any  other  substance  which  exerts  a reducing  action  on 
alkaline  solution  of  ferricyanide  of  potassium,  the  other  being  only  admis- 
sible, when  we  have  manganese  in  the  condition  of  a perfectly  definite 
higher  oxide,  and  free  from  other  bodies,  which  evolve  chlorine  on  boil- 
ing with  hydrochloric  acid. 

We  may  convert  into 


1.  Protosesquioxide  of  Manganese. 


a.  Py  Precipitation  as  Carbo- 
nate of  Protoxide  of  Manganese. 

All  the  soluble  salts  of  manga- 
nese with  inorganic  acids,  and  all  its 
salts  with  volatile  organic  acids ; 
also  those  of  its  salts  which,  insoluble 
in  water,  dissolve  in  hydrochloric 
acid  with  separation  of  their  acid. 


b.  Py  Precipitation  as  Hydrat- 
ed Protoxide  of  Manganese. 

All  the  compounds  of  manganese, 
with  the  exception  of  its  salts 
with  non-volatile  organic  acids. 


§ 109.] 


PROTOXIDE  OF  MANGANESE. 


183 


c.  Py  Precipitation  as  Sulphide 
of  Manganese. 

All  compounds  of  manganese 
without  exception. 


e.  By  direct  Ignition. 

All  oxygen  compounds  of  man- 
ganese ; salts  of  manganese  with 
readily  volatile  acids,  and  with  or- 
ganic acids. 

2.  Sulphide  of  Manganese. 

All  compounds  of  manganese  without  exception. 

3.  Pyrophosphate  of  Manganese. 

All  the  oxides  and  many  of  the  salts  of  manganese. 

The  method  1,  e,  is  simple  and  accurate,  but  seldom  admissible.  The 
method  1,  a,  is  the  most  usually  employed  ; if  one’s  choice  is  free,  it  is 
to  be  preferred  to  1,  b.  The  methods  1,  c,  and  2,  are  generally  used, 
when  the  methods  1,  a,  or  6,  cannot  be  adopted — say  on  account  of  the 
presence  of  a non-volatile  organic  substance,  and  also  when  we  have  to 
separate  manganese  from  other  metals.  The  latter  object  may  be  at- 
tained also  by  the  method  1,  d.  The  process  3,  is  very  convenient  and 
accurate  in  absence  of  alkaline  earth  and  heavy  metals.  The  phosphate 
and  borate  of  manganese  are  treated,  either  according  to  the  method 
1,  b , as  the  salts  precipitated  from  acid  solution  by  potassa  are  com- 
pletely decomposed  upon  boiling  with  excess  of  potassa,  or  according 
to  the  method  2.  In  silicates  the  manganese  is  determined  after  the 
separation  of  the  silicic  acid  (§  140),  according  to  1,  a,  or  3 ; for  the 
analysis  of  chromate  of  protoxide  of  manganese,  see  § 130  (chromic 
acid).  The  volumetric  method  by  reduction  of  ferricyanide  of  potas- 
sium is  comparatively  new,  and  especially  suited  for  technical  work, 
in  which  the  highest  degree  of  accuracy  is  not  required.  The  estima- 
tion of  manganese  from  the  quantity  of  chlorine  disengaged  upon  boil- 
ing the  oxides  with  hydTochloric  acid,  is  resorted  to,  more  particu- 
larly, to  determine  the  degrees  of  oxidation  of  manganese,  and  permits 
also  the  estimation  of  manganese  in  presence  of  other  metals  (see  Sec- 
tion V). 

1.  Determination  as  Protosesquioxide  of  Manganese. 

a.  Py  Precipitation  as  Carbonate  of  Protoxide  of  Manganese. 

The  precipitation  and  washing  are  effected  in  exactly  the  same  way 
as  directed  § 108,  1,  a (determination  of  zinc  as  oxide,  by  precipita- 
tion as  carbonate).  If  the  filtrate  is  not  absolutely  clear,  stand  it  in  a 
warm  place  for  twelve  to  twenty-four  hours.  A slight  precipitate  will 
then  separate,  which  is  collected  on  another  small  filter.  The  precipi- 
tate is  dried,  and  then  ignited  as  directed  § 53.  The  lid  is  removed 
from  the  crucible,  and  a strong  heat  maintained  until  the  weight  of  the 
residue  remains  constant.  Care  must  be  taken  to  prevent  reducing 


d.  Py  Separation  as  Pinoxide 
of  Manganese. 

All  compounds  of  manganese  in 
a slightly  acid  solution,  especially 
acetate  and  nitrate  of  protoxide 
manganese. 


184 


DETERMINATION. 


gases  finding  tlieir  way  into  the  crucible.  For  the  properties  of  the 
precipitate  and  residue,  see  § 78.  This  method,  if  properly  executed, 
gives  accurate  results.  The  principal  point  is  to  continue  the  applica- 
tion of  a sufficiently  intense  heat  long  enough  to  effect  the  object  in 
view.  It  is  necessary  also  to  ascertain  whether  the  residue  has  not  an 
alkaline  reaction,  and  having  removed  it  from  the  platinum  crucible, 
whether  it  dissolves  in  hydrochloric  acid  without  leaving  silica. 

b.  Py  Precipitation  as  Hydrated  Protoxide  of  Manganese. 

The  solution  should  not  be  too  concentrated,  and  it  is  best  to  have  it 
in  a platinum  dish.  Precipitate  with  solution  of  pure  soda  or  potassa, 
and  proceed  in  all  other  respects  as  in  a. 

If  phosphoric  acid  is  present,  or  boracic  acid,  the  fluid  must  be  kept 
boiling  for  some  time  with  an  excess  of  alkali.  For  the  properties  of  the 
precipitate,  see  § 78. 

c.  Py  Precipitation  as  Sulphide  of  Manganese. 

The  solution  contained  in  a comparatively  small  flask  and  no_t  too  di- 
lute is  first  mixed  with  chloride  of  ammonium  (if  an  ammonia  salt  is  not 
already  present  in  sufficient  quantity),  then — if  the  fluid  is  acid — with 
ammonia,  till  it  reacts  neutral  or  very  slightly  alkaline  ; now  add  yellow 
sulphide  of  ammonium  in  moderate  excess,  if  the  flask  is  not  already 
quite  full  up  to  the  neck,  add  water  till  it  is,  cork,  stand  it  in  a warm 
place  for  at  least  twenty-four  hours,  wash  the  precipitate  if  at  all  consi- 
derable, first  by  decantation,  then  on  the  filter,  using  water  containing 
sulphide  of  ammonium,  and  also  gradually  diminished  quantities  of 
chloride  of  ammonium  (finally  none).  In  decanting,  pour  the  fluid  in 
a flask,  not  on  the  filter.  After  decanting  three  times,  filter  the  fluids 
that  have  been  poured  off,  transfer  the  precipitate  to  the  filter,  aud  finish 
the  washing  as  above  directed,  without  interruption.  Keep  the  funnel 
covered  with  a glass  plate.  If  you  do  not  prefer  to  determine  according 
to  2,  proceed  as  follows : — Put  the  moist  filter  with  the  precipitate  into 
a beaker,  add  hydrochloric  acid,  and  warm  until  the  mixture  smells  no 
longer  of  sulphuretted  hydrogen  ; filter,  wash  the  residuary  paper  care- 
fully, and  precipitate  the  filtrate  as  directed  in  a.  The  results  are  satis- 
factory, compare  § 78,  e. 

d.  Py  Separation  as  Pinoxide  of  Manganese. 

Heat  the  solution  of  the  acetate  of  protoxide  of  manganese  or  some 
other  compound  of  the  protoxide  containing  but  little  free  acid,  after 
addition  of  a sufficient  quantity  of  acetate  of  soda,  to  from  50°  to  60°, 
and  transmit  chlorine  gas  through  the  fluid.  The  whole  of  the  man- 
ganese present  falls  down  as  binoxide  (Schiel, — Pivot,  Beudant,  and 
Daguin).  Wash,  first  by  decantation,  then  upon  the  filter  ; dry,  trans- 
fer the  precipitate  to  a flask,  add  the  filter  ash,  heat  with  hydrochloric 
acid,  filter,  and  precipitate  as  directed  in  a.  If  the  acetate  of  soda  is 
deficient,  and  especially  if  hydrochloric  acid  is  present,  it  may  happen 
that  the  precipitation  of  the  manganese  by  chlorine  is  not  quite  com- 
plete ; it  is  therefore  well,  after  filtering  off  the  peroxide,  to  treat  the 
filtrate  with  more  acetate  of  soda,  and  again  pass  chlorine.  The  sepa- 
ration of  manganese  as  binoxide,  by  evaporating  its  solution  in  nitric 
acid  to  dryness,  and  heating  the  residue,  finally  to  155°,  is  given  in 
Section  Y. 


§ 109.] 


PROTOXIDE  OF  MANGANESE. 


185 


[Bromine  may  be  most  advantageously  substituted  for  chlorine  gas. 
When  the  quantity  of  binoxide  is  small  it  may  be  directly  converted  into 
protosesquioxide  by  intense  ignition,  as  it  retains  but  one  or  two  per 
cent,  of  alkali.  It  may  also  be  estimated  as  pyrophosphate,  § 109,  3. 

e.  Dy  direct  Ignition. 

The  manganese  compound  under  examination  is  introduced  into  a pla- 
tinum crucible,  which  is  kept  closely  covered  at  first,  and  exposed  to  a 
gentle  heat ; after  a time  the  lid  is  taken  oft',  and  replaced  looselv  on  the 
crucible,  and  the  heat  is  increased  to  the  highest  degree  of  intensity, 
with  careful  exclusion  of  reducing  gases  ; the  process  is  continued  until 
the  weight  of  the  residue  remains  constant.  The  conversion  of  the 
higher  oxides  of  manganese  into  protosesquioxide  of  manganese  re- 
quires more  protracted  and  intense  heating  than  the  conversion  of  the 
protoxide.  In  fact,  it  can  hardly  be  effected  without  the  use  of  a gas 
blowpipe.  In  the  case  of  salts  of  manganese  with  organic  acids,  care 
must  always  be  taken  to  ascertain  whether  the  whole  of  the  carbon  has 
been  consumed ; and  should  the  contrary  turn  out  to  be  the  case,  the 
residue  must  either  be  dissolved  in  hydrochloric  acid,  and  the  solution 
precipitated  as  directed  in  a,  or  3 or  it  must  be  repeatedly  evaporated 
with  nitric  acid,  until  the  whole  of  the  carbon  is  oxidized.  The  method, 
if  properly  executed,  gives  accurate  results.  On  the  other  hand,  if  the 
directions  are  not  carefully  attended  to,  one  must  not  be  surprised  at 
considerable  differences.  In  the  ignition  of  salts  of  manganese  with 
organio  acids,  minute  particles  of  the  salt  are  generally  carried  away 
with  the  empyreumatic  products  evolved  in  the  process,  which,  of  course, 
tends  to  reduce  the  weight  a little. 

2.  Determination  as  Sulphide  of  Manganese. 

The  sulphide  precipitated  as  in  1,  c,  may  be  determined  in  this  form, 
as  follows : Dry,  transfer  the  precipitate  to  a crucible,  burn  the  filter, 
add  the  ashes,  strew  some  sulphur  on  the  top,  ignite  strongly  in  hydro- 
gen (till  it  becomes  black)  and  weigh  as  anhydrous  sulphide  of  man- 
ganese (II.  Bose  *),  compare  the  analogous  process  for  zinc,  § 108,  2. 

The  results  obtained  by  Oesten,  and  cited  by  Bose,  are  perfectly  sat- 
isfactory. 

This  method  is  shorter  and  more  convenient  than  dissolving  the  moist 
sulphide  in  hydrochloric  acid,  and  precipitating  with  carbonate  of  soda. 

The  protosulphate  and  all  the  oxides  of  manganese  may  be  sub- 
jected to  this  process  with  the  same  result. 

[3.  Determination  as  Pyrophosphate  of  Manganese. 

To  the  solution  of  manganese,  which  may  eontain  salts  of  ammonia  or 
alkalies,  phosphate  of  soda  is  added  in  large  excess  above  what  is  needful 
to  convert  the  manganese  into  phosphate.  The  white  precipitate  is  then 
redissolved  in  sulphuric  or  chlorhydric  acid,  the  liquid  is  heated  to 
boiling,  best  in  a platinum  dish,  and  ammonia  added  in  excess.  The 
boiling  is  continued  10 — 15  minutes,  whereby  the  white,  semi-gelatinous 
precipitate  first  formed  is  converted  into  rose-colored,  pearly  scales.  The 
whole  is  kept  hot  for  an  hour  longer,  then  filtered  and  washed  with  hot 
water  containing  a little  ammonia.  The  precipitate  of  ammonio-phos- 


* Pogg.  Anal.  110,  122. 


186 


DETERMINATION. 


[§  109. 


phate  of  manganese  is  dried,  separated  from  the  filter,  and  converted 
by  ignition  into  pyrophosphate.  Results  accurate,  see  8 78  (Gibbs* 
Henry  f).] 

4.  Volumetric  determination  by  the  Heduction  of  Ferricyanide  of 
Potassium  (E.  Lenssen  J). 

The  method  is  grounded  on  the  fact  that  if  a solution  of  protoxide  of 
manganese  which  contains  1 eq.  Fe203  to  1 eq.  MnO,  is  acted  on  by  ex- 
cess of  alkaline  solution  of  ferricyanide  of  potassium  at  a boiling  tem- 
perature, all  the  manganese  is  precipitated  as  binoxide,  while  a corre- 
sponding quantity  of  ferrocyanide  of  potassium  is  formed.  By  deter- 
mining the  latter,  the  amount  of  manganese  present  is  obtained. 

K3  Cfy2+2  K0  + Mn0,S03=2  K2  Cfy  f K0,S03+Mn02. 

Accordingly  1 eq.  manganese  gives  rise  to  2 eq.  ferrocyanide  of  potas- 
sium. Of  course  all  other  reducing  substances  must  be  absent,  and  the 
manganese  must  be  present  entirely  in  the  form  of  proto-salt.  If  the 
solution  contains  no  sesquioxide  of  iron,  the  precipitate  is  a combination 
of  much  binoxide,  with  little  protoxide,  not  always  in  the  same  propor- 
tions. In  performing  the  process,  mix  first  with  the  acid  solution  of 
protoxide  of  manganese  so  much  sesquichloride  of  iron  that  you  may  be 
sure  of  having  at  least  1 eq.  Fe203  to  1 eq.  MnO,  and  add  the  mixture 
gradually  to  a boiling  solution  of  ferricyanide  of  potassium,  previously 
rendered  strongly  alkaline  with  potassa  or  soda.  After  boiling  together 
a short  time  the  brownish-black  precipitate  becomes  granular  aud  less 
bulky.  Allow  to  cool  completely , filter  off  and  wash  the  precipitate, 
acidify  the  filtrate  with  hydrochloric  acid,  and  estimate  the  ferrocyanide 
of  potassium  with  permanganate,  according  to  § 147,  II.,  g.  a.  If  the 
liquid  is  filtered  hot,  the  results  are  too  high,  as  the  filter  in  this  case 
has  a reducing  action.  The  method  may  be  shortened,  as  follows  : After 
boiling,  transfer  the  solution,  together  with  the  precipitate,  to  a measur- 
ing flask,  allow  to  cool,  fill  up  to  the  mark  with  water,  shake,  and  allow 
to  settle.  Filter  through  a dry  filter,  take  out  a certain  quantity  with  a 
pipette,  and  determine  the  ferrocyanide  in  this.  A slight  source  of  error 
is  here  introduced  by  disregarding  the  volume  of  the  precipitate.  The 
results  adduced  by  Lenssen  are  very  satisfactory.  I have  myself  repeat- 
edly tested  this  method,  and  I have  to  remark  as  follows : — 

a.  If  ferricyanide  of  potassium  is  long  boiled  with  pure  potassa,  a small 
quantity  of  ferrocyanide  is  invariably  produced. 

b.  The  potassa  must  be  quite  free  from  organic  substances,  and  should 
therefore,  if  there  is  any  doubt  on  this  point,  be  fused  in  a silver  dish 
before  use,  otherwise  the  error  alluded  to  in  a may  be  considerably  in- 
creased. 

c.  The  complete  washing  of  the  voluminous  precipitate  is  attended 
with  so  much  difficulty  and  loss  of  time  as  to  render  the  method  more 
troublesome  than  a gravimetric  analysis. 

d.  The  abridged  method,  on  the  other  hand,  may  be  of  great  service 
in  certain  cases,  especially  when  a series  of  manganese  determinations 
have  to  be  made,  the  manganese  not  being  in  too  minute  quantities,  and 
the  highest  degree  of  accuracy  not  being  required.  In  my  laboratory, 
by  employing  a slight  excess  of  sesquioxide  of  iron,  97*9 — 100*12 — 


Am.  Jour.  Sci.  2d  Ser.  44.  p.  216.  f Am.  Jour.  Sci.  2d  Ser. , 47,  p.  130. 
% Journ.  f.  prakt.  Chem.  80,  408. 


I 


§ 110.]  PROTOXIDE  OF  NICKEL.  187 

98*21 — 98*99,  and  100*4  were  obtained,  instead  of  100.  The  inaccuracy 
increases  on  using  a large  excess  of  the  iron.* 

5.  Volumetric  determination  by  boiling  the  higher  oxides  with  hydro- 
chloric acid , and  estimating  the  chlorine  evolved. 

The  methods  here  employed  will  be  found  all  together  in  the  Special 
Part  under  “Valuation  of  Manganese  Ores.” 

§ 110. 

3.  Protoxide  of  Nickel. 

a.  Solution. 

Many  of  the  salts,  of  protoxide  of  nickel  are  soluble  in  water.  Those 
which  are  insoluble,  as  also  the  pure  protoxide,  in  its  common  modifica- 
cation,  dissolve,  without  exception,  in  hydrochloric  acid.  The  peculiar 
modification  of  protoxide  of  nickel,  discovered  by  Genth,  which  crystal- 
lizes in  octahedra,  does  not  dissolve  in  acids,  but  is  rendered  soluble  by 
fusion  with  bisulphate  of  potassa.  Metallic  nickel  dissolves  slowly,  with 
evolution  of  hydrogen  gas,  when  warmed  with  dilute  hydrochloric  or 
sulphuric  acid  ; in  nitric  acid,  it  dissolves  with  great  readiness.  Sul- 
phide of  nickel  is  but  sparingly  soluble  in  hydrochloric  acid,  but  it  dis- 
solves readily  in  nitrohydrochloric  acid.  Peroxide  of  nickel  dissolves 
in  hydrochloric  acid,  upon  the  application  of  heat,  to  protochloride,  with 
evolution  of  chlorine. 

b.  Determination. 

Protoxide  of  nickel  is  always  weighed  as  such  (§  79).  The  compounds 
of  nickel  are  converted  into  the  pure  protoxide,  usually  by  precipitation 
as  hydrated  protoxide,  preceded,  in  some  instances,  by  precipitation  as 
sulphide  of  nickel,  or  by  ignition. 

We  may  convert  into 


PROTOXIDE 

a.  By  Precipitation  as  Hydrated 
Protoxide  or  Sesquioxide  of  Nickel. 

All  the  salts  of  nickel  with  in- 
organic acids  which  are  soluble  in 
water,  and  all  its  salts  with  volatile 
organic  acids ; likewise  all  salts  of 
nickel  which,  insoluble  in  water, 
dissolve  in  the  stronger  acids,  with 
separation  of  their  acid. 


OF  NICKEL. 

b.  By  Precipitation  as  Sulphide 
of  Nickel. 

All  compounds  of  nickel  with- 
out exception. 


c.  By  Ignition. 

The  salts  of  nickel  with  readily  volatile  oxygen  acids, 
or  with  such  oxygen  acids  as  are  decomposed  at  a high 
temperature  (carbonic  acid,  nitric  acid). 

The  method  c is  very  good,  but  seldom  admissible.  The  method  a is 
most  frequently  employed.  In  the  presence  of  sugar,  or  other  non-vola- 
tile organic  substance,  it  cannot  be  used.  In  this  case  we  must  either 


* Zeitschr.  f.  Anal.  Chem.  3,  209. 


188 


DETERMINATION. 


ignite  and  thereby  destroy  the  organic  matter  before  precipitating,  or 
we  must  resort  to  the  method  b , which  otherwise  is  hardly  used  except 
in  separations.  The  combinations  of  the  protoxide  of  nickel  with 
chromic,  phosphoric,  boracic,  and  silicic  acids  are  analyzed  according  to 
the  methods  given  under  the  several  acids. 

Determination  as  Protoxide  of  Nickel. 

a.  By  Precipitation  as  Hydrated  Protoxide  of  Nickel. 

Mix  the  solution  with  pure  solution  of  potassa  or  soda  in  excess, 
heat  for  some  time  nearly  to  ebullition,  decant  3 or  4 times,  boiling 
up  each  time,  filter,  wash  the  precipitate  thoroughly  with  hot  water, 
dry  and  ignite  intensely  (Russell  *)  (§  53).  The  precipitation 
is  best  effected  in  a platinum  dish ; in  presence  of  nitrohydrochloric 
acid,  or,  if  the  operator  does  not  possess  a sufficiently  capacious  dish  of 
the  metal,  in  a porcelain  dish  ; glass  vessels  do  not  answer  the  purpose 
so  well.  Presence  of  ammoniacal  salts,  or  of  free  ammonia,  does  not 
interfere  with  the  precipitation.  For  the  properties  of  the  precipitate 
and  residue,  see  § 79.  This  method,  if  properly  executed,  gives  very 
accurate  results.  The  thorough  washing  of  the  precipitate  is  a most 
essential  point.  It  is  necessary  also  to  ascertain  whether  the  residue 
has  not  an  alkaline  reaction,  and  whether  it  dissolves  completely  in 
hydrochloric  acid. 

[Addition  of  solution  of  hypochlorite  of  soda  to  the  hot  liquid,  after 
treatment  with  caustic  soda,  converts  the  protoxide  into  sesquioxide , 
which  washes  more  easily  than  the  protoxide,  and  is  otherwise  treated 
like  the  latter.] 

b.  By  Precipitation  as  Sulphide  of  Nickel. 

This  requires  the  greatest  care  and  attention  when  sulphide  of  am- 
monium is  employed. 

a.  The  moderately  dilute  cold  solution  of  nickel  contained  in  a proper 
sized  flask  is,  if  necessary,  neutralized  with  ammonia  (the  reaction  should 
be  rather  slightly  acid  than  alkaline)  : chloride  of  ammonium  is  added, 
if  not  already  present  in  sufficient  quantity,  and  then  hydrosulphate  of 
sulphide  of  ammonium,  as  long  as  a precipitate  is  produced.  (The 
NF4S,  HS  should  be  perfectly  saturated  with  HS;  it  may  be  colorless  or 
light-yellow.)  A large  excess  of  the  reagent  must  be  avoided.  After 
mixing,  fill  the  flask  with  water  up  to  the  neck,  cork,  and  allow  to  stand 
about  twenty  four  hours  without  warming,  but  in  a moderately  warm 
place.  The  precipitate  has  now  settled,  and  the  clear  supernatant  fluid 
is  colorless  or  slightly  yellow.  Decant,  filter,  and  wash  as  described  in 
the  case  of  sulphide  of  manganese  (§  109,  1,  c ).  (Filtrate  and  wash- 
water  must  be  colorless  or  slightly  yellow.)  Dry  the  precipitate  in  the 
funnel,  and  transfer  as  completely  as  possible  from  the  filter,  to  a beaker ; 
the  filter  is  incinerated  in  a coil  of  platinum  wire,  or  upon  the  lid  of  a 
crucible,  and  the  ash  added  to  the  dry  precipitate.  The  precipitate  is 
now  treated  with  concentrated  nitrohydrochloric  acid,  and  the  mixture 
digested  at  a gentle  heat,  until  the  whole  of  the  sulphide  of  nickel  is 
dissolved,  and  the  undissolved  sulphur  appears  of  a pure  }^ellow ; the 
fluid  is  then  diluted,  filtered,  and  the  filtrate  precipitated,  &c.,  as  di- 
rected in  a.  For  the  properties  of  the  precipitate,  see  § 79.  The 
method,  if  properly  executed,  gives  accurate  results. 

If  the  solution  contains  free  ammonia,  or  no  salt  of  ammonia,  the 


* Joum.  Chem.  Soc.  16,  58. 


111.] 


PROTOXIDE  OF  COBALT. 


189 


fluid  filtered  off  from  the  sulphide  of  nickel  possesses  always  a more  or 
less  brownish  tint,  and  contains  sulphide  of  nickel  (§  79,  c),  which  must 
be  regained  by  acidifying  with  acetic  acid  and  boiling.  If  the  precipi- 
tate is  not  washed  as  directed,  some  nickel  is  very  likely  to  pass  through 
with  the  wash-water.  If  the  filter  were  not  incinerated,  but  treated  at 
once,  together  with  the  precipitate,  with  nitrohydrochloric  acid,  the  so- 
lution of  the  sulphide  of  nickel  would  contain  organic  substances,  and 
the  soda  or  potassa  would  accordingly  afterwards  fail  to  effect  the  com- 
plete precipitation  of  the  nickel. 

(3.  Mix  the  slightly  acidified  solution  of  nickel  with  bicarbonate  of 
ammonia,  so  that  the  free  acid  may  be  neutralized,  and  the  solution  may 
contain  a small  excess  of  the  bicarbonate  of  ammonia,  together  with  free 
carbonic  acid,  and  then  pass  hydrosulphuric  acid  gas  through  the  mix- 
ture. Precipitation  will  promptly  ensue.  Filter,  and  treat  the  precip- 
itate as  in  a. 

[y.  When  a boiling  solution  of  sulphide  of  sodium*  is  added  to  a 
boiling  solution  of  a salt  of  nickel,  sulphide  of  nickel  is  thrown  down 
completely,  and  may  be  filtered  and  washed  with  hot  water  without  the 
least  oxidation.  It  is  best  to  add  some  acetic  acid  before  filtering,  to 
destroy  any  excess  of  sulphide  of  sodium.  (GiBBS.f)] 

It  is  not  advisable  to  convert  the  sulphide  of  nickel  in  Ni.2S,  by  ignit- 
ing in  hydrogen  with  addition  of  sulphur,  and  in  this  form  to  weigh  it, 
as  the  composition  of  the  residue  is  not  quite  constant.  (H.  Pose.) 

c.  Dy  direct  Ignition. 

The  same  method  as  described  § 109,  1,  e.  (Manganese.) 

§in. 

4.  Protoxide  of  Cobalt. 

a.  Solution. 

Protoxide  of  cobalt  and  its  compounds  behave  with  solvents  like  the 
corresponding  compounds  of  nickel ; metallic  cobalt  like  metallic  nickel. 
The  protosesquioxide  of  cobalt  obtained  by  Schwarzenberg  in  microscopic 
octahedra  does  not  dissolve  in  boiling  hydrochloric  acid,  or  nitric  acid,  nor 
in  nitrohydrochloric  acid  ; but  it  dissolves  in  concentrated  sulphuric  acid, 
and  in  fusing  bisulphate  of  potassa. 

b.  Determination. 

Cobalt  may  be  weighed  as  metallic  cobalt , protoxide  of  cobalt , sulphate 
of  protoxide  of  cobalt , and  nitrite  of  cobalt  and  potassa.  The  conversion 
into  protoxide  is  often  preceded  by  precipitation  as  hydrated  sesquioxide, 
and  conversion  into  the  sulphate  by  precipitation  as  sulphide  of  cobalt. 

We  may  convert  into 

1.  Metallic  Cobalt. 

All  salts  of  cobalt  that  may  be  reduced  directly  by  hydrogen  gas  (chlo- 
ride of  cobalt,  nitrate  of  protoxide  of  cobalt,  carbonate  of  protoxide  of 
cobalt,  &c.)  and  all  the  oxides. 

* [ Pure  sulphide  of  sodium  may  be  procured  by  dissolving  crystallized  sul- 
phide (NaS.  9 HO),  in  alcohol  of  90  per  cent,  and  recrystallizing  two  or  three 
times  from  the  solvent.  The  pure  salt  is  dried  in  vacuo,  and  the  white  ef- 
floresced mass  preserved  in  a well-stoppered  bottle.  (Gibbs. )] 

[ f Am.  Jour.  Sci.  2d  Ser.  37,  350.] 


190 


DETERMINATION. 


2.  Protoxide  of  Cobalt. 

All  salts  of  cobalt  which  are  soluble  in  water,  or  in  stronger  acids,  with 
separation  of  their  acid,  except  those  with  non-volatile  organic  acids. 
Also  all  the  higher  oxides,  and  all  salts  whose  acids  are  destroyed  or 
expelled  by  ignition. 

3.  Sulphate  of  Protoxide  of  Cobalt. 

All  compounds  of  cobalt  without  exception. 

4.  Nitrite  of  Cobalt  and  Potassa. 

All  compounds  of  cobalt  soluble  in  water  or  acetic  acid. 

1.  Determination  as  Metallic  Cobalt. 

Evaporate  the  solution  of  chloride  of  cobalt,  or  of  nitrate  of  protoxide 
of  cobalt,  which  must  be  free  from  sulphuric  acid  and  alkali,  in  a weighed 
crucible,  to  dryness ; cover  the  crucible  with  a lid  having  a small  aper- 
ture in  the  middle,  conduct  through  this  a moderate  current  of  pure 
dry  hydrogen  gas,  and  then  apply  a gentle  heat,  which  is  to  be  increased 
gradually  to  intense  redness.  . When  the  reduction  is  considered  complete, 
let  the  reduced  metal  cool  in  the  current  of  hydrogen  gas,  and  weigh ; 
ignite  again  in  the  same  way  and  repeat  the  process  until  the  weight  of 
the  reduced  metal  remains  constant.  The  results  are  accurate.  For  the 
properties  of  cobalt,  see  § 80. 

[The  oxides  of  cobalt  which  have  been  precipitated  by  an  alkali  after 
ignition  may  be  reduced  in  the  same  manner.  The  metal  retains  a small 
portion  of  alkali  which  may  be  removed  by  washing  with  hot  water  down 
to  unweighable  traces.  Unless  alkali  absolutely  free  from  silica,  and 
platinum  vessels  be  employed  in  the  precipitation,  the  metal,  after  weigh- 
ing, should  be  dissolved,  the  solution  evaporated  to  dryness  on  the  water- 
bath,  that  any  residue  of  silica  maybe  separated.] 

As  regards  the  apparatus  to  be  employed,  see  fig.  47,  p.  181. 

[2.  Determination  as  Protoxide  of  Cobalt. 

a.  Dy  Precipitation  as  Hydrated  Sesquioxide. 

The  solution  is  precipitated  exactly  as  described  for  nickel,  with  solution 
of  soda  under  addition  of  a hypochlorite.  § 110,  a.  The  precipitate  is 
also  further  treated  as  there  directed,  with  the  important  difference  that 
the  dried  precipitate  is  ignited  and  cooled  in  a stream  of  pure  carbonic 
acid  gas  until  the  weight  remains  constant.  See  § 80. 

When  precipitated  as  hydrated  sesquioxide  with  reagents  free  from 
silica,  &c.,  the  precipitate  retains  but  trifling  traces  of  alkali,  and  the 
method  is  very  accurate. 

b.  Dy  Ignition. 

Carbonate  and  nitrate  of  cobalt  are  ignited  in  a stream  of  carbonic 
acid  as  above.  Organic  salts  are  ignited  in  the  air  until  carbon  is  burned 
off,  and  then  in  an  atmosphere  of  carbonic  acid.] 

3.  Determination  as  Sulphate  of  Protoxide  of  Cobalt. 

a.  Dy  direct  Conversion. 

The  solution  is  evaporated  to  dryness,  in  a platinum  dish  or  platinum 


111.] 


PROTOXIDE  OP  COBALT. 


191 


crucible  * — (directly,  if  it  contains  sulphate  of  protoxide  of  cobalt ; but 
if  it  contains  a volatile  acid,  after  addition  of  a slight  excess  of  sulphuric 
acid) — and  the  residue  cautiously  heated,  at  a gradually  increased  tem- 
perature, which  is  finally  raised  to  gentle  redness  : the  application  of 
heat  is  continued  until  no  more  fumes  escape  and  the  weight  of  the  cruci- 
ble remains  constant.  In  order  to  avoid  spirting  while  heating,  it  is  well 
to  hold  the  flame  above  the  crucible,  and  let  it  play  on  the  cover. 

After  weighing,  the  salt  is  treated  with  hot  water.  If  this  fails  to  effect 
complete  solution  (a  sign  that  the  salt  has  become  basic)  the  residue  is 
dissolved  in  hydrochloric  acid,  and  the  amount  of  sulphuric  acid  is  then 
estimated  in  the  solution,  as  directed  § 132;  the  difference  will  be  the 
protoxide  of  cobalt.  The  results  are  accurate. 

For  the  properties  of  sulphate  of  protoxide  of  cobalt  see  § 80. 

b.  Preceded  by  Precipitation  as  Sulphide  of  Cobalt. 

Precipitate,  decant,  filter  and  wash  exactly  as  directed  for  sulphide  of 
manganese  (§  109,  1,  c),  dry,  and  redissolve  as  directed  § 110,  b , a (Sul- 
phide of  nickel.) 

The  solution  obtained  contains  invariably  sulphuric  acid ; the  amount 
of  the  cobalt  is  determined  according  to  3,  a,  taking  care  to  evaporate  the 
fluid,  which  contains  nitrohydrochloric  acid,  in  a porcelain  dish,  with 
addition  of  sulphuric  acid,  to  dryness,  before  transferring  the  residue,  with 
a little  water,  to  the  platinum  dish.  The  results  are  accurate. 

For  the  properties  of  the  sulphide  of  cobalt  see  § 80.  The  sulphide 
of  cobalt  cannot  be  brought  into  a weighable  form  by  ignition  in  hydrogen, 
as  the  residue  is  a variable  mixture  of  different  sulphides  (H.  Pose). 

4.  Determination  as  Nitrite  of  Cobalt  and  Potassa  (used  principally 
in  cases  of  separation). 

Mix  the  cobalt  solution,  which  must  not  be  too  dilute  (at  the  most, 
300  parts  of  water  to  1 of  protoxide  of  cobalt),  with  a concentrated  solu- 
tion of  nitrite  of  potassa  ; add  acetic  acid  in  quantity,  a little  more  than 
sufficient  to  redissolve  the  precipitate,  which  is  at  first  produced  in  the 
solution  by  the  free  potassa  and  carbonate  of  potassa  contained  in  the 
nitrite.  Cover  the  beaker  with  a clock-glass,  and  let  it  stand  12  to  24 
hours  in  a warm  place.  Collect  the  yellow  precipitate  on  a weighed  filter, 
wash  thoroughly  with  an  aqueous  solution  of  neutral  acetate  of  potassa 
(containing  10  per  cent,  of  the  salt),  to  which  some  nitrite  of  potassa  is 
added,  displace,  finally,  the  last  portion  of  solution  of  acetate  of  potassa 
still  adhering  to  the  precipitate,  by  means  of  spirit  of  wine  of  80  per 
cent.,  dry,  ignite,  incinerate  the  filter,  moisten  the  whole  with  sulphuric 
acid,  drive  off  the  excess  of  the  latter  (see  § 97,  1),  and  weigh  the 
residue  which  consists  of  2 (Co  O,  S 03)  + 3 (K  O,  S 03).  Gibbs  and 
Genth  f have  obtained  good  results  by  this  method. 

100  parts  of  the  residue  are  equivalent  to  18’014  parts  of  Co  O. 

[Or  dissolve  the  nitrite  of  cobalt  and  potassa  in  hydrochloric  acid, 
precipitate  by  potassa,  reduce  the  washed  precipitate  by  hydrogen,  and 
weigh  the  washed  metal.  (H.  Rose.)] 

[To  weigh  the  precipitate  dried  at  100°  is  not  recommended,  since 
Erdmann  has  shown  that  its  content  of  water  and  nitrogen  is  variable. 
See  § 80.] 


* The  operation  must,  at  all  events,  be  finished  in  a platinum  vessel, 
f Annal.  d.  Chem.  u.  Pharm.  104,  309. 


192 


DETERMINATION. 


[§  112. 


§ 112. 

5.  Protoxide  of  Iron. 

a.  Solution . 

Many  of  the  compounds  of  protoxide  of  iron  are  soluble  in  water. 
The  compounds  insoluble  in  water  dissolve  almost  without  exception  in 
hydrochloric  acid,  in  which  the  pure  protoxide  also  is  soluble ; the  solu- 
tions, if  not  prepared  with  perfect  exclusion  of  air,  and  with  solvents 
absolutely  free  from  air,  contain  invariably  more  or  less  sesquichloride. 
In  cases  where  it  is  wished  to  avoid  the  chance  of  oxidation,  the  solution 
of  the  compound  of  protoxide  of  iron  is  effected  in  a small  flask,  through 
which  a slow  current  of  carbonic  acid  gas  is  passed,  the  transmission  of  the 
gas  being  continued  until  the  solution  is  cold.  Many  native  proto-com- 
pounds of  iron  cannot  be  thus  dissolved.  They  are,  indeed,  rendered 
soluble  by  fusing  with  carbonate  of  soda,  but  in  this  process  the  protox- 
ide of  iron  is  converted  into  sesquioxide  It  is  therefore  advisable  to 
heat  such  substances  (in  the  finest  powder)  with  a mixture  of  3 parts 
concentrated  sulphuric  acid  and  1 part  water  in  a strong  sealed  tube  of 
Bohemian  glass  for  2 hours  at  about  210°,  or — in  the  case  of  silicates — 
to  warm  them  with  a mixture  of  2 parts  hydrochloric  acid  and  1 part 
strong  hydrofluoric  acid  in  a covered  platinum  dish  (A.  Mitscherlich  *. 
See  also  Cooke’s  method  of  solution,  p.  — ).  Metallic  iron  dissolves  in 
hydrochloric  acid,  and  in  dilute  sulphuric  acid,  with  evolution  of  hydro- 
gen, as  protochloride  or  sulphate  of  protoxide  respectively ; in  warm  ni- 
tric acid  it  dissolves  as  nitrate  of  sesquioxide,  and  in  nitro-hydrochloric 
acid  as  sesquichloride. 

b.  Determination. 

Protoxide  of  iron  may  be  estimated  1,  by  dissolving,  converting  into 
sesquioxide  and  determining  the  latter  gravimetrically  or  volumetrically ; 
2,  by  precipitating  as  sulphide,  and  weighing  it  as  such,  or  determining 
it  after  conversion  into  sesquioxide  ; 3,  by  a direct  volumetric  method ; 
4,  by  treating  with  terchloride  of  gold,  and  weighing  the  reduced  gold. 

The  methods  1 and  2 are,  of  course,  only  applicable  when  no  sesqui- 
oxide is  present  with  the  protoxide ; the  method  2 is  scarcely  ever  used 
except  for  separations.  The  methods  included  under  3 are  adapted  to 
most  cases  and,  in  absence  of  other  reducing  substances,  are  espe- 
cially worthy  of  recommendation.  The  method  4 will  be  briefly  treated 
of  in  the  supplement  to  §§  112  and  113. 

As  the  determination  of  iron  as  sesquioxide  belongs  to  § 113,  and  as 
the  process  for  precipitating  the  protoxide  as  sulphide  is  the  same  as 
that  for  precipitating  the  sesquioxide  in  this  form,  nothing  remains  for 
us  here  but  to  describe  the  methods  of  converting  the  protoxide  into  the 
sesquioxide  and  the  processes  included  under  3. 

1.  Methods  of  converting  Protoxide  of  Iron  into  Sesquioxide. 

a.  Methods , applicable  in  all  cases. 

Heat  the  solution  of  protoxide  of  iron  to  be  oxidized  with  hydro- 
chloric acid  and  add  small  portions  of  chlorate  of  potassa,  till  the  fluid, 
even  after  warming  for  some  time,  still  smells  strongly  of  chlorine.  Our 
object  may  be  also  attained  by  passing  chlorine  gas  or — in  the  case  of 


* Journ.  f.  prakt.  Chem.  81,  11(1. 


PROTOXIDE  OF  IRON-. 


193 


§ 112*] 

small  quantities — by  addition  of  chlorine  water.  If  the  solution  is  re- 
quired to  be  free  from  excess  of  chlorine,  it  is  finally  heated,  till  all  odor 
of  that  gas  has  disappeared. 

b.  Methods  which  are  only  suitable  when  the  iron  is  to  be  subsequently 
precipitated  by  ammonia , as  hydrated  sesquioxide. 

Mix  the  solution  of  the  protoxide  of  iron  in  a flask  with  a little 
hydrochloric  acid,  if  it  does  not  already  contain  any ; add  some  nitric 
acid,  and  heat  the  mixture  for  some  time  to  incipient  ebullition.  The 
color  of  the  fluid  will  show  whether  the  nitric  acid  has  been  added  in 
sufficient  quantity.  Though  an  excess  of  nitric  acid  does  no  harm,  still 
it  is  better  to  avoid  adding  too  much  on  account  of  the  subsequent  pre- 
cipitation. In  concentrated  solutions,  the  addition  of  nitric  acid  pro- 
duces a dark-brown  color,  which  disappears  upon  heating.  This  color  is 
owing  to  the  nitric  oxide  formed  dissolving  in  the  still  unoxidized  por- 
tion of  the  solution  of  the  protoxide. 

c.  Methods  which  can  be  employed  only  when  the  sesquioxide  of  iron 
is  to  be  determined  volumetrically . 

Add  to  the  hydrochloric  solution  small  quantities  of  artificially  pre- 
pared iron-free  binoxide  of  manganese,  till  the  solution  is  of  a dark 
olive  green  color  from  the  formation  of  sesquichloride  of  manganese ; 
boil  till  this  coloration  and  the  odor  of  chlorine  have  disappeared  (Fr. 
Mohr)  ; or  you  may  add  pure  permanganate  of  potassa  (in  crystals  or 
concentrated  solution)  till  the  fluid  is  just  red  and  then  boil,  till  the  red 
color  and  chlorine-odor  have  vanished.  These  methods  present  the  ad- 
vantage of  permitting  complete  oxidation  without  the  use  of  any  consid- 
erable excess  of  the  oxidizing  agent. 

2.  Estimation  by  Volumetric  Analysis. 

a.  Marguerite’s  Method. 

This  method  is  based  upon  the  following  principle : — 

If  we  add  to  a solution  of  protoxide  of  iron,  containing  an  excess  of 
sulphuric  acid,  permanganate  of  potassa,  the  former  is  oxidized  at  the 
expense  of  the  latter  [10  (Fe  O,  S03)  -f  8 S 03  + K O,'  Mn207  — 5 (Fe2 
03,  3 S 03)  -f  K O,  S 03  -f  2 (Mn  O,  S 03)].  Now  if  we  possess  a solu- 
tion of  permanganate  of  potassa,  and  know  how  much  iron  100  c.  c.  of 
it  can  convert  from  the  condition  of  protoxide  to  that  of  sesquioxide, 
we  can,  with  this,  readily  determine  an  unknown  quantity  of  iron ; we 
have  simply,  for  this  purpose,  to  dissolve  the  iron  in  acid,  in  the  form 
of  protoxide,  to  oxidize  the  solution  accurately,  and  note  how  many  c. 
c.  of  the  solution  of  permanganate  of  potassa  have  been  used  to  accom- 
plish that  object. 

a.  Determination  of  the  Strength  of  the  Solution  of  Permanganate 
of  Potassa. 

The  process  of  preparing  a solution  of  permanganate  of  potassa  having 
been  described  already  in  § 65,  3,  I will  at  once  proceed  to  give  the  sev- 
eral methods  employed  to  determine  the  strength  of  the  solution. 

Either  of  the  three  subjoined  methods  may  be  selected  for  the  pur- 
pose ; or,  the  strength  having  been  determined  by  one  method,  it 
may,  by  way  of  control,  be  determined  once  more  by  one  of  the  other 
methods. 

Solution  of  permanganate  of  potassa  prepared  from  the  pure  crystal- 

13 


194 


DETERMINATION. 


L§  112. 


lized  salt,  does  not  alter,  if  carefully  kept ; on  the  contrary,  if  it  contains 
free  potassa  or  manganate  of  potassa,  it  suffers  gradual  decomposition, 
and  each  analysis,  made  after  an  interval  of  even  only  a day,  must  be 
preceded  by  a fresh  determination  of  its  strength. 

aa.  Determination  of  the  Strength  by  means  of  Metallic  Iron. 

Weigh  off  accurately  about  0'2  grm.  of  thin,  clean  iron  wire  (piano- 
forte wire)  ; introduce  this  into  a small  long-necked  flask,  add  about  20 
c.  c.  of  dilute  sulphuric  acid,  and  the  same  quantity  of  water,  secure  the 
flask  in  an  oblique  position,  by  means  of  a retort-holder ; transmit 
through  it  a slow  current  of  carbonic  acid,  and  then  heat  the  fluid  to 
gentle  ebullition. 

Fig.  48  shows  the  arrangement  of  the  apparatus.  When  the  iron  has 
dissolved,  allow  to  cool,  keeping  up  the  current  of  carbonic  acid,  then 


Fig.  48. 


fill  the  flask  two-thirds  with  distilled  water ; smear  the  rim  with  a little 
tallow,  pour  the  contents  cautiously  into  a beaker  of  about  400  c.  c. 
capacity,  and  transfer  the  last  particles  from  the  flask  to  the  beaker  by 
repeated  rinsing  with  cold  water.  The  total  quantity  of  fluid  should  be 
about  200  c.  c.  Place  the  beaker  on  a sheet  of  white  paper,  or  better, 
on  a sheet  of  glass,  with  white  paper  underneath. 

Fill  a Gay-Lussac’s  or  Geissler’s  burette  of  30  c.  c.  capacity,  divided 
into  e.  c.  (see  §§  22,  23,  figs.  13  and  14),  up  to  zero,  with  solution  of 
permanganate  of  potassa,  of  which  take  care  to  have  ready  a sufficient 
quantity,  perfectly  clear  and  uniformly  mixed. 

Now  add  the  permanganate  to  the  iron  solution,  stirring  the  latter  all 
4he  while  with  a glass  rod.  At  first  the  red  drops  disappear  very  rapid- 
ly, then  more  slowly.  The  fluid,  which  at  first  was  nearly  colorless, 
gradually  acquires  a yellowish  tint.  From  the  instant  the  red  drops  be- 
gin to  disappear  more  slowly,  add  the  permanganate  with  more  caution 
and  in  single  drops,  until  the  last  drop  imparts  to  the  fluid  a faint,  but 
unmistakable  reddish  color,  which  remains  on  stirring.  A little  practice 
will  enable  you  readily  to  hit  the  right  point.  As  soon  as  the  fluid  in 
the  burette  has  sufficiently  collected  again,  read  off,  and  mark  the  num- 


PROTOXIDE  OF  IRON. 


195 


§ 112.] 

ber  of  c.  c.  used.  The  reading  off  must  be  performed  with  the  greatest 
exactness  (see  § 22) ; the  whole  error  should  not  amount  to  c.  c. 

If  0*2  grm.  iron  have  taken  from  20  to  30  c.  c.  of  permanganate,  the 
latter  may  be  considered  to  be  of  the  proper  degree  of  concentration  for 
most  determinations  of  iron.  If  much  less  has  been  used  in  the  process, 
the  solution  is  too  concentrated.  In  that  case  add  to  the  entire  quantity 
a sufficient  amount  of  water  to  give  it  approximately  the  right  degree 
of  concentration;  then  repeat  the  above  experiment  with  afresh  amount 
of  iron.  If,  on  the  other  hand,  considerably  more  than  30  c.  c.  of  perman- 
ganate have  been  used  for  0*2  grm.  iron,  the  solution  is  not  exactly  unfit 
for  use,  but  working  with  it  becomes  the  more  tedious  and  inconvenient 
the  more  its  degree  of  concentration  differs  from  that  given  above. 

When  you  have  completed  the  experiment  with  a solution  of  approxi- 
mately proper  concentration,  calculate,  by  a simple  proportion,  how  much 
iron  100  c.  c.  of  the  solution  will  convert  from  the  state  of  protoxide  to 
that  of  sesquioxide.  Supposing,  for  instance,  you  have  used  to  0*210 
grm.  iron,  2 3’ 5 c.  c.  of  the  permanganate,  then  we  say 

23*5  : 100::  0*210  : x se:=:0*8936  (grm.  iron). 

As  the  accuracy  of  all  estimations  made  with  the  solution  of  perman- 
ganate of  potassa  depends  upon  the  correct  determination  of  the  strength, 
it  is  always  advisable  to  repeat  the  experiment. 

As  even  the  purest  iron  wire  is  not  chemically  pure,  but  contains  a 
little  carbon,  it  is  well,  in  analyses  requiring  the  very  highest  degree  of 
accuracy,  to  reduce  the  weight  of  the  iron  wire  used  in  the  process,  by 
multiplication  with  0*997,  to  the  corresponding  weight  of  chemically  pure 
iron.  This  reduction  is  based  upon  the  generally  correct  supposition 
that  the  wire  contains  0*3  per  cent,  of  extraneous  matter. 

If,  in  the  two  experiments  made  for  the  purpose  of  determining  the 
strength  of  the  solution  of  permanganate  of  potassa,  the  quantities  of  iron 
respectively  corresponding  to  100  c.  c.  of  solution,  differ  only  about  1,  2, 
or  3 mgrm.  (per  grm.),  the  results  may  be  considered  perfectly  satisfac- 
tory. But  if  the  difference  is  considerably  greater,  a third  experiment 
must  be  made. 

If  there  is  a deficiency  of  free  acid  in  the  solution  of  iron,  the  fluid 
acquires  a brown  color,  turns  turbid,  and  deposits  a brown  precipitate 
(binoxide  of  manganese  and  sesquioxide  of  iron).  The  same  may  happen 
also  if  the  solution  of  permanganate  of  potassa  is  added  too  quickly,  or 
if  the  proper  stirring  of  the  iron  solution  is  omitted  or  interrupted. 
Experiments  attended  with  abnormal  manifestations  of  the  kind  should 
always  be  rejected.  That  the  fluid  reddened  by  the  last  drop  of  solution 
of  permanganate  of  potassa  added,  loses  its  color  again  after  a time,  need 
create  no  surprise  or  uneasiness ; this  decolorization  is,  in  fact,  quite 
inevitable,  as  a dilute  solution  of  free  permanganic  acid  cannot  keep  long 
undecomposed. 

bb.  Determination  of  the  Strength  by  means  of  Sulphate  of  Protoxide 
of  Iron  and  Ammonia. 

Weigh  off,  with  the  greatest  accuracy,  about  1*4  grm.  of  the  pure 
salt  prepared  according  to  the  directions  given  in  § 65,  4,  after  powder- 
ing the  crystals,  and  pressing  between  sheets  of  smooth  blotting-paper. 
Dissolve  in  about  200  c.  c.  distilled  water,  add  about  20  c.  c.  dilute 
sulphuric  acid,  and  proceed  as  in  aa. 

As  sulphate  of  protoxide  of  iron  and  ammonia,  contains  exactly  \ of 


190 


DETERMINATION. 


[§  112. 


its  weight  of  iron,  the  calculation  required  to  show  the  value  of  100  c.  c. 
of  permanganate  is  very  simple.  Supposing,  for  instance,  25  c.  c.  of  per- 
manganate to  have  been  consumed  to  1*400  grm.  of  the  iron  salt,  then, 


and  25  : 100  : : 0*2  : x ; cr=0*8 

If  the  sulphate  of  protoxide  of  iron  and  ammonia  used  is  not  pure,  if, 
for  instance,  it  contains  bases  isomorphous  with  protoxide  of  iron  (pro- 
toxide of  manganese,  magnesia,  &c.)  ; or  if  it  contains  sesquioxide,  or  is 
used  in  a moist  condition,  the  result  will  of  course  be  too  high. 

cc.  Determination  of  the  Strength  by  means  of  Oxalic  Acid. 

This  method  is  based  upon  the  following  principle : — 

If  solution  of  permanganate  of  potassa  is  added  to  a warm  solution  of 
oxalic  acid,  mixed  with  sulphuric  acid,  the  liberated  permanganic  acid 
instantly  oxidizes  the  oxalic  acid  to  carbonic  acid  [5  C2  03  -4-  3 S 03-f 
K O,  Mn,  07  = 10  C 02  -f  2 (Mn  O,  S03)+KO,S  03].  For  the  oxida- 
tion of  1 eq.  oxalic  acid  (C2  03)  and  2 eq.  iron  (in  the  state  of  protoxide) 
equal  quantities  of  permanganic  acid  are  accordingly  required ; there- 
fore, 63  parts  (1  eq.)  of  crystallized  oxalic  acid  correspond,  in  reference  to 
the  oxidizing  action  of  permanganic  acid,  to  56  parts  (2  eq.)  of  iron. 

By  dissolving  6*3  grm.  pure  crystallized  oxalic  acid  (§  65,  1),  or  4*5 
grm.  of  the  pure  hydrate,  dried  at  100°,  in  water,  to  1 litre  of  fluid,  a deci- 
normal  solution  of  oxalic  acid  is  obtained,  which  is  exactly  suited  to  our 
present  purpose.  50  c.  c.  of  this  solution,  which  correspond  to  0*315 
grm.  crystallized  oxalic  acid,  or  0*28  grms.  iron,  are  introduced  into  a 
beaker,  diluted  with  about  100  c.  c.  of  water,  from  6 to  8 c.  c.  of  cone, 
sulphuric  acid  added,  and  the  fluid  heated  to  about  60°.  The  beaker  is 
then  placed  on  a sheet  of  white  paper,  and  permanganate  added  from  the 
burette,  with  stirring.  The  red  drops  do  not  disappear  at  first  very 
rapidly,  but  when  once  the  reaction  has  fairly  set  in,  they  continue  for 
some  time  to  vanish  instantaneously.  As  soon  as  the  red  drops  begin 
to  disappear  more  slowly,  the  solution  of  permanganate  of  potassa  must 
be  added  with  great  caution  ; if  proper  care  is  taken  in  this  respect,  it  is 
easy  to  complete  the  reaction  with  a single  drop  of  permanganate ; this 
completion  of  the  reaction  is  indicated  with  beautiful  distinctness  in  the 
colorless  fluid.  The  number  of  c.  c.  used  corresponds  to  0*28  grm.  iron. 

If  the  oxalic  acid  was  not  perfectly  dry,  or  not  quite  pure,  the  result  of 
the  experiment  will,  of  course,  lead  to  fixing  the  strength  of  the  solution  of 
permanganate  of  potassa  too  high.  Instead  of  pure  oxalic  acid,  Saint-Gilles 
has  proposed  to  use  crystallized  oxalate  of  ammonia  (N  H4  O,  C2  03  -}-  aq.). 
This  can  easily  be  prepared  in  the  pure  state,  keeps  well,  and  can  be 
weighed  with  accuracy.  It  is  not  however  advisable  to  keep  a standard 
solution  of  this  salt  in  store,  as  it  is  liable  to  spoil.  71  parts  of  the 
crystallized  salt  correspond  to  56  parts  iron. 


Of  the  foregoing  three  methods  of  standardizing  solution  of  permanga- 
nate of  potassa,  the  first  is  the  one  originally  proposed  by  Marguerite. 
Sulphate  of  protoxide  of  iron  and  ammonia  was  first  proposed  by  Fr.  Mohr, 
and  oxalic  acid  by  Hempel,  as  agents  suitable  for  the  purpose.  With 


§ H2-] 


PROTOXIDE  OF  IRON. 


197 


absolutely  pure  and  thoroughly  dry  reagents,  and  proper  attention,  all 
three  methods  give  correct  results. 

For  myself,  I prefer  the  first  method,  as  the  most  direct  and  positive, 
the  only  doubtful  point  about  it  being  the  question  whether  the  assump- 
tion that  the  iron  wire  contains  99*7  per  cent,  of  chemically  pure  iron  is 
quite  correct ; this,  however,  is  of  very  trifling  importance,  as  the  error 
could  not  exceed  y^-  or  T2y  per  cent.  But  the  other  two  methods  are,  as  may 
readily  be  seen,  somewhat  more  convenient,  since  in  one  of  them  the 
trouble  is  saved  of  preparing  the  solution  of  iron,  and  in  the  other  there 
is,  moreover,  no  need  of  weighing.  These  advantages,  however,  which 
were  considerable  when  the  impure  permanganate  solution  that  was  used 
required  fresh  standardizing  every  day,  have  now  lost  their  value,  as  the 
pure  solution,  now  generally  employed,  keeps  unaltered. 

For  the  analysis  of  very  dilute  solutions  of  iron,  e.g .,  chalybeate  water, 
in  which  the  amount  of  iron  may  be  very  approximately  determined  with 
great  expedition,  by  direct  oxidization  with  permanganate,  a very  dilute 
standard  solution  must  be  prepared  ; of  which  100  c.  c.  correspond  to  say 
0T  grm.  iron.  Such  a solution  should  be  directly  standardized  with  corre- 
spondingly small  quantities  of  iron,  or  the  iron-double-salt,  and  boiled 
water  should  be  used. 

In  experiments  of  this  kind,  the  fact  that  a certain  quantity  of  perman- 
ganate is  required  to  impart  a distinct  color  to  pure  acidified  water  (which 
is  of  no  consequence  in  operations  where  the  concentrated  solution  is  used) 
must  be  taken  into  consideration  ; for  where  the  solution  used  is  so  highly 
dilute,  it  takes  indeed  a measurable  quantity  of  it  to  impart  the  desired 
reddish  tint  to  the  amount  of  water  employed.  In  such  cases,  the  volume 
of  the  solution  of  iron  used  for  standardizing  the  permanganate  and  the 
volume  of  the  weak  ferruginous  solution  subjected  to  analysis  should  be 
the  same,  and  either  the  two  solutions  should  contain  about  the  same  quan- 
tity of  iron,  or,  by  means  of  a special  experiment,  it  is  ascertained  how 
many  Jy  c.  c.  of  the  permanganate  are  required  to  impart  the  desired  pale 
red  color  to  the  same  volume  of  acidified  water.  In  the  latter  case,  these 
yy  c.  c.  will  be  deducted  from  the  amount  of  permanganate  used  in  the 
regular  experiments. 

/3.  Performance  of  the  Analytical  Process. 

This  has  been  fully  indicated  in  a.  The  compound  to  be  examined  is 
dissolved,  preferably  with  application  of  a current  of  carbonic  acid  (see 
fig.  48,  p.  194),  in  water,  or  dilute  sulphuric  acid,  allowed  to7  cool  in  the 
current  of  carbonic  acid,  and  suitably  diluted  (if  practicable,  the  solution 
of  a substance  containing  about  0*2  grm.  iron  should  be  diluted  to  about 
200  c.  c.)  ; if  free  acid  is  not  yet  present  in  sufficient  quantity,  about 
20  c.  c.  of  dilute  sulphuric  acid  are  added,  and  then  standard  perman- 
ganate from  the  burette,  to  incipient  reddening  of  the  fluid.  The  volume 
of  standard  solution  used  is  then  read  off.  The  strength  of  the  solution 
of  permanganate  being  known,  the  quantity  of  iron  present  in  the  examined 
fluid  is  found  by  a very  simple  calculation.  Suppose  100  c.  c.  of  solution 
of  permanganate  of  potassa  to  correspond  to  0*98  grm.  iron,  and  25  c.  c. 
of  the  solution  to  have  been  used  to  effect  the  oxidation  of  the  protoxide 
of  iron  in  the  examined  compound  ; then 

100  : 25  ::  0-98  : cc;  cc=0*245. 

The  quantity  of  iron  originally  present  in  the  form  of  protoxide 
amounted  accordingly  to  0'245  grm. 


198 


DETERMINATION. 


[§  112. 


For  the  method  of  determining  the  total  amount  of  iron  present  in  a 
solution  containing  both  protoxide  and  sesquioxide  of  that  metal,  I refer 
to  § 113;  for  that  of  determining  the  amount  of  each  separately,  to 
Section  V. 

Note  on  the  Determination  of  Iron  in  Hydrochloric  Acid 
Solution  by  the  foregoing  Method. 

The  foregoing  process  was  long  considered  to  be  the  most  convenient 
and  best  for  the  estimation  of  iron.  Lowenthal  and  Lenssen*  have 
shown  that  in  solutions  containing  hydrochloric  acid ',  it  is  essential  that 
the  standardizing  of  the  reagent  and  the  actual  analysis  be  performed 
under  the  same  circumstances  as  regards  dilution,  amount  of  acid,  and 
temperature.  Besides  the  proper  reaction  10  Fe  O -{-  Mn2  07  — 5 F e.2  03 
+ 2 Mn  O,  the  collateral  reaction  7 H Cl  + Mn207:=5  Cl + 2 Mn  C1  + 
7 H O also  takes  place,  in  consequence  of  which  a little  chlorine  is  libe- 
rated. This  chlorine  does  not  oxidize  the  protoxide  of  iron  in  the  case 
of  considerable  dilution,  but  there  occurs  a condition  of  equilibrium  in 
the  fluid  containing  protoxide  of  iron,  chlorine,  and  hydrochloric  acid, 
which  is  destroyed  by  addition  of  a further  quantity  of  either  body 
(Lowenthal  and  Lenssen,  loc.  cit.).  But  since  it  is  difficult  to  preserve 
the  above  condition  of  obtaining  correct  results,  the  following  proceed- 
ing is  adopted,  in  presence  of  chlorine. 

Standardize  the  permanganate  by  means  of  iron  dissolved  in  dilute 
sulphuric  acid,  make  the  iron  solution  to  be  tested  up  to  ^ litre,  add  50 
c.  c.  to  a large  quantity  of  water  acidified  with  sulphuric  acid,  add  per- 
manganate from  burette,  then  again  50  c.  c.  of  the  iron  solution,  perman- 
ganate again,  &c.,  &c.  The  numbers  obtained  at  the  third  and  fourth 
time  are  taken.  These  are  constant,  while  that  obtained  the  first  time, 
and  sometimes  also  the  second  time,  ditfers.  The  result  multiplied  by  5 
gives  exactly  the  quantity  of  permanganate  proportional  to  the  amount 
of  protoxide  of  iron  present. 

I believe  that  the  reason  why  the  attention  of  analysts  was  not  pre- 
viously directed  to  the  important  influence  of  hydrochloric  acid  in  this 
process,  lay  in  the  fact  that  it  was  not  customary  to  crystallize  the  per- 
manganate before  employing  it — the  crude  solution,  which  contains  much 
chloride  of  potassium,  being  used.  The  experiments  were  consequently 
performed  in  the  presence  of  free  hydrochloric  acid,  even  when  sulphuric 
acid  alone  was  employed  for  dissolving  or  acidifying.  Hence  the  differ- 
ences between  the  results  with  sulphuric  and  hydrochloric  acid  solutions 
were  not  so  large  as  they  are  now,  when  we  work  with  the  pure  perman- 
ganate. 

h.  Penny’s  Method  (recommended  subsequently  by  Schabus). 

If  bichromate  of  potassa  is  added  to  a strongly  acid  solution  of  prot- 
oxide of  iron,  the  latter  is  converted  into  sesquioxide,  whilst  the  chromic 
acid  is  reduced  to  sesquioxide  of  chromium  (6  Fe  0 + 2 Cr  03=3  Fe2  03  + 
Cr2  03). 

Now,  with  OT  eq.  bichromate  of  potassa=  14*759  grm.  dissolved  to 
1 litre  of  fluid,  0*6  eq.  — 16*8  grm.  iron  may  be  converted  from  the  state 
of  protoxide  to  that  of  sesquioxide,  and  50  c.  c.  of  the  above  solution 
correspond  accordingly  to  0*84  grm.  iron. 

* Zeitschrift  f.  analyt.  Chem.  1,  329.  See  also  361. 


SESQUIOXIDE  OF  IRON. 


199 


§ 113.] 


Care  must  be  taken  to  use  perfectly  pure  bichromate  of  potassa ; the 
salt  is  heated  in  a porcelain  crucible  until  it  is  just  fused;  it  is  then 
allowed  to  cool  under  the  desiccator,  and  the  required  quantity  weighed 
off  when  cold.  Besides  the  above  solution,  another  should  also  be  pre- 
pared, ten  times  more  dilute,  and  containing  accordingly  0*01  eq.  of 
bichromate  of  potassa  in  the  litre. 

It  is  always  advisable  to  test  the  correctness  of  the  standard  solution 
of  bichromate  of  potassa,  by  oxidizing  with  it  a known  amount  of  pure 
iron  dissolved  to  protoxide  (see  p.  194,  aa). 

The  analytical  process  is  performed  as  follows : — 

The  solution  of  protoxide  of  iron  is  sufficiently  diluted,  mixed  with  a 
sufficient  quantity  of  hydrochloric  or  dilute  sulphuric  acid,  and  the 
standard  solution  of  bichromate  of  potassa  slowly  added  from  the  burette, 
the  liquid  being  stirred  all  the  while  with  a thin  glass  rod.  The  fluid, 
which  is  at  first  nearly  colorless,  speedily  acquires  a pale  green  tint, 
which  changes  gradually  to  a darker  chrome-green.  A very  small  drop 
of  the  mixture  is  now  from  time  to  time  taken  out  by  means  of  the 
stirring-rod,  and  brought  into  contact  with  a drop  of  a solution  of  ferri- 
cyanide  of  potassium  on  a porcelain  plate,  which  has  been  spotted  with 
several  of  such  drops.  When  the  blue  color  thereby  produced  begins  to 
lose  the  intensity  which  it  exhibited  on  the  first  trials,  and  to  assume  a 
paler  tint,  the  addition  of  the  solution  of  bichromate  of  potassa  must  be 
more  carefully  regulated  than  at  first,  and  towards  the  end  of  the  pro- 
cess a fresh  essay  must  be  made,  and  with  larger  drops  than  at  first, 
after  each  new  addition  of  two  drops,  and  finally,  even  of  a single  drop ; 
drops  must  also  be  left  for  some  time  in  contact  before  the  observation 
is  taken.  When  no  further  blue  coloration  ensues,  the  oxidation  is  ter- 
minated. From  the  remarkable  sensitiveness  of  the  reaction,  the  exact 
point  may  be  easily  hit  to  a drop.  To  heighten  the  accuracy  of  the  re- 
sults, the  dilute  (ten  times  weaker)  standard  fluid  should,  just  at  the 
end  of  the  process,  be  substituted  for  the  concentrated  solution  of  bichro- 
mate of  potassa. 

If  exactly  0*84  grm.  of  the  substance  to  be  analyzed  have  been  dis- 
solved, the  numbers  of  half  c.  c.  used  of  the  two  standard  fluids  show 
how  many  per  cents,  and  tenths  per  cent,  respectively  of  pure  iron  the 
analyzed  substance  contains  in  the  form  of  protoxide.  For  the  manner 
of  proceeding  in  presence  of  sesquioxide  of  iron,  I refer  to  § 113.  If 
there  is  a deficiency  of  free  acid  in  the  solution,  brown  chromate  of  ses- 
quioxide of  chromium  may  form,  upon  which  the  solution  of  protoxide 
of  iron  exercises  no  longer  a deoxidizing  action. 


§ H3. 

6.  Sesquioxide  of  Iron. 

a.  Solution. 

Many  of  the  compounds  Qf  sesquioxide  of  iron  are  soluble  in  water. 
Pure  sesquioxide  of  ir  on  and  most  of  those  of  its  compounds  which  are 
insoluble  in  water,  dissolve  in  hydrochloric  acid,  but  many  of  them  only 
slowly  and  with  difficulty ; compounds  of  this  nature  are  best  dissolved 
in  concentrated  hydrochloric  acid,  in  a flask,  with  the  aid  of  heat ; which, 
however,  should  not  be  allowed  to  reach  the  boiling-point ; the  compound 
must,  moreover,  be  finely  powdered,  and  even  then  it  will  often  take 


200 


DETERMINATION. 


[§  US. 


many  hours  to  effect  complete  solution.  Iron  ores  insoluble  in  hydro* 
chloric  acid  are  treated  like  the  corresponding  compounds  of  protoxide 
of  iron  [best  by  fusion  with  carbonate  of  soda]. 

b.  Determination. 

Sesquioxide  of  iron  is  usually  weighed  as  such,  but  sometimes  as  sul- 
phide (§  81).  It  may,  however,  be  estimated  also  indirectly,  and  also  by 
volumetric  analysis,  both  directly  and  after  reduction  to  protoxide.  The 
conversion  of  compounds  of  iron  into  sesquioxide  is  effected  either  by 
precipitation  as  hydrated  sesquioxide,  preceded  in  some  cases  by  precipi- 
tation as  sulphide  of  iron,  or  as  succinate  or  basic  acetate  or  basic 
formiate  of  sesquioxide  of  iron ; or  by  ignition.  While  the  volumetric 
and  the  now  seldom-used  indirect  methods  are  applicable  in  almost  all 
cases,  we  may  convert  into 

1.  Sesquioxide  of  Iron. 

a.  By  Precipitation  as  Hydrated  Sesquioxide. 

All  salts  soluble  in  water  with  inorganic  or  volatile  organic  acids,  and 
likewise  those  which,  insoluble  in  water,  dissolve  in  hydrochloric  acid, 
with  separation  of  their  acid. 

b.  By  Precipitation  as  Sidphide  of  Iron. 

All  compounds  of  iron  without  exception. 

c.  By  Precipitation  as  Succinate  of  Sesquioxide  of  Iron  ‘ and 

d.  By  Precipitation  as  Basic  Acetate  or  Formiate  of  Sesqui- 

oxide of  Iron. 

The  compounds  enumerated  sub  a. 

e.  By  Ignition. 

All  salts  of  sesquioxide  of  iron  with  volatile  oxygen  acids. 

2.  Sulphide  of  Iron. 

All  compounds  of  iron  without  exception. 

The  method  1,  e,  is  the  most  expeditious  and  accurate,  and  is  there- 
fore preferred  in  all  cases  where  its  application  is  admissible.  The 
method  1,  a,  is  the  most  generally  used.  The  methods  1,  b , and  2, 
serve  principally  to  effect  the  separation  of  the  sesqui oxide  of  iron  from 
other  bases ; they  are  resorted  to  also  in  certain  instances  where  a is  in- 
applicable, especially  in  cases  where  sugar  or  other  non-volatile  organic 
substances  are  present ; and  also  to  estimate  the  sesquioxide  of  iron  in 
its  compounds  with  phosphoric  acid  and  boracic  acid.  The  methods  1, 
c and  1,  d are  used  exclusively  in  separations.  For  the  manner  of  de- 
termining the  sesquioxide  of  iron  in  the  chromate  and  silicate,  I refer 
to  §§  130  and  140.  The  volumetric  methods  for  estimating  the  sesqui- 
oxide are  used  in  technical  experiments  almost  to  the  exclusion  of  all 
others,  and  are  very  frequently  employed  in  scientific  analyses. 

1.  Determination  as  Sesquioxide  of  Iron. 

a.  By  Precipitation  as  Hydrated  Sesquioxide. 

Mix  the  solution  in  a dish  or  beaker  with  ammonia  in  excess,  heat 


SESQUIOXIDE  OF  IRON. 


201 


§ H3.] 


nearly  to  boiling,  decant  repeatedly  on  to  a filter,  wash  the  precipitate 
carefully  with  hot  water,  dry  thoroughly  (which  very  greatly  reduces 
the  bulk  of  the  precipitate),  and  ignite  in  the  manner  directed  in  § 53. 

For  the  properties  of  the  precipitate  and  residue,  see  § 81.  The 
method  is  free  from  sources  of  error.  The  precipitate,  under  all  circum- 
stances, even  if  there  are  no  fixed  bodies  to  be  washed  out,  must  be  most 
carefully  and  thoroughly  washed,  since,  should  it  retain  any  traces  of 
chloride  of  ammonium,  a portion  of  the  iron  would  volatilize  in  the  form 
of  sesquichloride.  It  is  also  highly  advisable  to  dissolve  the  weighed 
residue,  or  a portion  of  it,  in  strong  hydrochloric  acid,  to  see  whether  it 
is  quite  free  from  silicic  acid. 

b.  By  Precipitation  as  Sulphide  of  Iron. 

The  solution,  in  a not  too  large  flask,  is  mixed  with  ammonia,  till  all 
the  free  acid  is  neutralized.  (In  the  absence  of  organic,  non-volatile 
substances  this  leads  to  the  precipitation  of  a little  hydrated  sesquioxide, 
which,  however,  is  of  no  consequence.)  Add  chloride  of  ammonium,  if 
not  already  present  in  sufficient  quantity,  then  colorless  or  yellowish  sul- 
phide of  ammonium  in  moderate  excess,  lastly  water,  till  the  fluid  reaches 
to  the  neck  of  the  flask.  Cork  it  up  and  stand  in  a warm  place  till  the 
precipitate  has  subsided,  and  the  supernatant  fluid  has  a clear  yellowish 
appearance  (without  a tinge  of  green).  Wash  as  directed  in  the  case  of 
sulphide  of  manganese  (§  109,  1,  c).  Neglect  of  any  of  these  precautions 
will  occasion  some  loss  of  substance,  the  sulphide  of  iron  gradually  com- 
bining with  the  oxygen  of  the  air,  and  passing  thus  into  the  filtrate  as 
protosulphate.  As  this  sulphate  is  reprecipitated  by  the  sulphide  of 
ammonium  present,  the  filtrate  assumes,  in  such  cases,  a greenish  color, 
and  gradually  deposits  a black  precipitate,  the  separation  of  which  is 
highly  promoted  by  addition  of  chloride  of  ammonium.  [See  remarks 
in  [ ] § 81,  5,  c.  p.  122.] 

When  the  operation  of  washing  is  completed,  the  moist  precipitate  (if 
it  is  not  dried  and  determined  according  to  2)  is  put,  together  with  the 
filter,  into  a beaker,  some  water  added,  and  then  hydrochloric  acid,  until 
the  whole  is  redissolved.  Heat  is  now  applied,  until  the  solution  smells 
no  longer  of  sulphuretted  hydrogen  ; the  fluid  is  then  filtered  into  a 
flask,  the  residual  paper  carefully  washed,  and  the  filtrate  oxidized  by 
heating  with  nitric  acid  (see  § 112,  1);  the  oxidized  solution  is  finally 
precipitated  with  ammonia,  as  in  a. 

If  a solution  of  potassio-,  sodio-,  or  ammonio-tartrate  of  sesquioxide  of 
iron  contains  a considerable  excess  of  alkaline  carbonate,  the  precipitation 
of  the  iron  as  sulphide  is  prevented  to  a greater  or  less  extent  (Blumenau). 
In  such  cases  the  fluid  must  therefore  be  nearly  neutralized  with  an  acid, 
before  the  precipitation  with  the  sulphide  of  ammonium  can  be  effected. 

c.  By  Precipitation  as  Succinate  of  Sesquioxide  of  Iron. 

The  solution,  in  a flask,  is  mixed  with  very  dilute  ammonia,  drop  by 
drop,  until  a small  portion  of  the  iron  precipitates  in  the  form  of  hydrated 
sesquioxide ; a gentle  heat  is  then  applied,  to  ascertain  whether  or  not 
the  precipitate  will  redissolve.  If  it  redissolves,  the  addition  of  dilute 
ammonia  is  continued,  until  the  application  of  heat  fails  to  redissolve  the 
precipitate  formed.  If  it  remains  undissolved,  and  the  fluid  still  exhibits 
a brownish  red  color,  all  the  preliminary  conditions  requisite  for  pre- 


202 


DETERMINATION. 


[§113 


cipitation  with  succinate  of  ammonia  are  fulfilled.  But  should  the  fluid 
appear  colorless,  this  is  a sign  that  too  much  ammonia  has  been  added ; 
in  which  case  it  will  be  necessary  to  add  a small  portion  of  hydrochloric 
acid,  and  then  again  some  ammonia,  until  the  desired  point  is  attained. 
To  the  fluid  thus  prepared  is  now  added  a perfectly  neutral  solution  of 
succinate  of  ammonia,  as  long  as  a precipitate  forms ; a gentle  heat  is 
then  applied,  and  the  fluid  allowed  to  cool ; when  perfectly  cold  it  is 
filtered,  and  the  precipitate  washed,  first  with  cold  water,  finally  with 
warm  ammonia — which  operation,  depriving  the  precipitate  in  a very 
great  measure  of  its  acid,  imparts  a darker  tint  to  it.  The  washed  pre- 
cipitate is  dried  upon  the  filter  in  the  funnel,  and  then  converted  into 
sesquioxide  of  iron,  by  ignition  (§  53).  The  object  of  washing  the  pre- 
cipitate with  ammonia  is  to  remove  part  of  the  acid,  since,  were  the  pre- 
cipitate simply  washed  with  water,  a portion  of  the  sesquioxide  of  iron 
might  suffer  reduction  upon  the  subsequent  ignition  of  the  succinate.  If 
there  is / reason  to  apprehend  that  this  has  actually  taken  place,  some 
nitric  acid  is  added  to  the  precipitate,  evaporated,  and  the  ignition  re- 
peated. For  the  properties  of  the  precipitate,  see  § 81.  The  results  are 
accurate. 

d.  By  Precipitation  as  Basic  Acetate  of  Sesquioxide  of  Iron. 

Mix  the  solution  of  sesquioxide  of  iron  [containing  not  more  than 

1 grm.  of  oxide  to  litre]  in  a flask,  if  it  contains  much  free  acid,  with 
carbonate  of  soda  or  ammonia  until  the  acid  is  nearly  neutralized ; then 
add  to  the  solution  which  is  still  clear,  but  already  of  a deep  red  color, 
neutral  acetate  of  soda  or  of  ammonia,  and  a few  drops  of  acetic  acid  in 
slight  excess ; and  boil  till,  on  removing  the  lamp,  the  precipitate  settles 
clear.  Wash  repeatedly  by  boiling  and  decantation,  and  finally  on  the 
filter  with  boiling  water,  which  should  contain  a little  acetate  of  ammo- 
nia ; dry,  ignite  (§53),  and  weigh  the  sesquioxide  obtained.  It  is 
advisable  to  add  a few  drops  of  nitric  acid  to  the  residue,  evaporate,  and 
ignite  again,  to  see  whether  the  weight  remains  constant.  The  residue 
must  show  no  alkaline  reaction  when  moistened  with  water.  The  results 
are  accurate.  It  is  often  preferable  to  dissolve  the  precipitate  of  the 
basic  acetate  in  hydrochloric  acid,  and  to  precipitate  the  solution  accord- 
ing to  a [see  also  Reichardt’s  method],  § 81,  e.  The  formiates  of  soda 
and  ammonia  may  be  advantageously  substituted  for  the  acetates  as  pre- 
cipitants  (§  Sif-/*). 

e.  By  Ignition. 

Expose  the  compound,  in  a covered  crucible,  to  a gentle  heat  at  first, 
and  gradually  to  the  highest  degree  of  intensity ; continue  the  operation 
until  the  weight  of  the  residuary  sesquioxide  of  iron  remains  constant. 

2.  Determination  as  Anhydrous  Sulphide  of  Iron. 

The  hydrated  sulphide  of  iron  obtained,  as  in  1,  b , may  be  very  con- 
veniently determined  by  conversion  into  the  anhydrous  sulphide.  The 
process  is  the  same  as  for  zinc  (§  108,  2).  The  heat  to  which  it  is  finally 
exposed  in  the  current  of  hydrogen  must  be  strong,  as  an  excess  of  sul- 
phur is  retained  with  some  obstinacy.  In  fact,  it  is  advisable  after 
weighing  to  re-ignite  in  hydrogen  and  weigh  a second  time.  It  is  of  no 
importance  if  the  hydrated  sulphide  has  oxidized  on  drying. 

Protosulphate  and  sesquioxide  of  iron  can  be  transformed  into  sul- 


113.] 


SESQUIOXIDE  OF  IRON. 


203 


p'liide  in  the  same  manner,  after  having  been  dehydrated  by  ignition  in 
a porcelain  crucible  (H.  Rose  *). 

The  results  obtained  by  Oesten,  and  adduced  by  Rose,  as  well  as  those 
obtained  in  my  own  laboratory,  are  exceedingly  satisfactory.  (Expt. 
No.  75.) 

3.  Determination  by  Volumetric  Analysis. 

a.  Preceded  by  Deduction  of  the  Sesquioxide  to  Protoxide. 

The  volumetric  methods  which  come  under  this  head  are  based  upon 
the  reduction  of  the  sesquioxide  to  protoxide,  and  the  estimation  of  the 
•latter.  We  have,  accordingly,  to  occupy  ourselves  simply  with  the 
reduction  of  the  solution  of  the  sesquioxide,  the  other  part  of  the  pro- 
cess having  been  fully  discussed  in  § 112  (Protoxide  of  Iron).  The 
reduction  of  sesquioxide  of  iron  can  be  effected  by  many  substances 
(zinc,  protochloride  of  tin,  sulphuretted  hydrogen,  sulphurous  acid,  &c.), 
but  only  those  can  be  used  with  advantage,  an  excess  of  which  may  be 
added  with  impunity.  If  an  excess  must  be  very  carefully  avoided,  or, 
being  added,  must  be  carefully  removed,  the  method  becomes  trouble- 
some, and  a ready  source  of  inaccuracy  is  introduced.  On  these  grounds, 
although  its  action  is  somewhat  slow,  zinc,  unquestionably,  deserves  the 
preference  before  all  other  reducing  agents. 

Heat  the  hydrochloric  or  sulphuric  acid  solution,  which  must  contain 
a moderate  excess  of  acid,  but  be  free  from  nitric  acid,  in  a small  long- 
necked flask,  placed  in  a slanting  position ; drop  in  small  pieces  of  iron- 
free  zinc  (§  60),  and  conduct  a slow  current  of  carbonic  acid  through 
the  flask  (fig.  48,  p.  194).  Evolution  of  hydrogen  gas  begins  at  once, 
and  the  color  of  the  solution  becomes  paler  in  proportion  as  the  sesqui- 
oxide changes  to  protoxide.  Apply  a moderate  heat,  to  promote  the 
action  ; and  add  also,  if  necessary,  a little  more  zinc.  As  soon  as  the 
hot  solution  is  completely  decolorized  (one  cannot  judge  of  the  perfect 
deoxidation  of  a cold  solution  so  well,  as  the  color  of  the  sesquichloride 
of  iron  is  deeper  in  the  heat),  allow  to  cool  completely  in  the  stream  of 
carbonic  acid ; to  hasten  the  cooling  the  flask  may  be  immersed  in  cold 
water  ; then  dilute  the  contents  with  water,  pour  off  and  wash  carefully 
into  a beaker,  leaving  behind  any  undissolved  zinc,  and  also  (as  far  as 
possible)  any  flocks  of  lead  that  may  have  separated  from  the  zinc,  and 
proceed  as  directed  in  § 112,  2.  If  the  solution  contains  metals  precipi- 
table  by  zinc,  these  will  separate,  and  may  render  filtration  necessary. 
In  this  case  the  filtrate  must  be  again  heated  with  zinc  before  using  the 
standard  solution.  If  iron-free  zinc  cannot  be  procured,  the  percentage 
of  iron  in  the  metal  used  must  be  determined,  and  weighed  portions  of 
it  employed  in  the  process  of  reduction  ; the  known  amount  of  iron  con- 
tained in  the  zinc  consumed  is  then  subtracted  from  the  total  amount  of 
ir^n  found. 

[6.  Without  Previous  Deduction  to  Protoxide.  Oudemans’ 
Method. \ 

The  principle  consists  in  adding  a reducing  agent  to  the  solution  till 
the  sesquioxide  is  entirely  converted  into  protoxide,  and  then  determin- 
ing the  amount  of  the  reducing  agent  used. 


Pogg.  Anna!  110,  126. 


f Fresenius’  Zeitschrift,  YI.  129. 


204 


DETERMINATION. 


[§  H3. 


This  method  depends  upon  the  fact  that  hyposulphite  of  soda  may  re- 
duce sesquioxide  of  iron  to  protoxide  in  accordance  with  the  equation 
Ee3  Cl3  + 2 (Na  O,  S2  02)  = 2 Fe  Cl  + Na  O,  S4  05  + Na  Cl.  In  order 
that  this  reaction  serve  for  analytical  purposes  it  is  necessary,  1,  that  a 
certain — not  too  great — proportion  of  free  acid  be  present ; 2,  that  the 
iron  solution  be  rather  concentrated ; and,  3,  that  a minute  amount  of 
solution  of  a salt  of  protoxide  of  copper  be  present,  which  acts  to  trans- 
fer oxygen  from  the  iron  to  the  hyposulphite,  being  reduced  by  the  lat- 
ter to  suboxide  and  carried  again  to  protoxide  by  the  sesquisalt  of  iron. 
We  require : — 

a.  A Solution  of  Hyposulphite  of  Soda. 

This  may  be  made  by  dissolving  25  grm.  of  the  purest  commercial 
salt  in  1 litre  of  water. 

b.  A Standard  Solution  of  a Sesquisalt  of  Iron. 

This  is  prepared  by  dissolving  5*617  grm.  of  fine  piano-wire,  assumed 
to  contain  99*7  per  cent,  of  iron,  in  hydrochloric  acid  in  a slanting  long- 
necked flask,  oxidizing  the  solution  with  chlorate  of  potassa,  removing 
the  excess  of  chlorine  by  protracted  gentle  boiling,  and  finally  diluting 
the  solution  to  1 litre;  or  by  dissolving  24*1  grm.  of  pure  ammonia- 
iron-alum  (see  p.  93)  in  1 litre  of  water. 

c.  A Solution  of  Sulphate  of  Copper  containing,  say,  10  per  cent,  of 
the  crystallized  salt. 

d.  A Solution  of  Sulphocyanide  of  Potassium. 

The  standard  of  the  hyposulphite-solution  must  be  fixed  by  aid  of  the 
accurately  prepared  iron-solution,  as  follows : — 

20  c.  c.  of  the  iron-solution  are  measured  into  a small  flask  or  beaker,  well 
acidified  with  hydrochloric  acid  ; one  drop  of  the  copper  solution  is  added, 
and  enough  sulphocyanide  to  make  the  liquid  of  a deep  red  color.  The  hy- 
posulphite (about  20  c.  c.)  is  added  from  a burette,  rapidly  at  first,  after- 
wards slowly  and  cautiously,  until  the  red  color  is  discharged.  The  iron- 
solution  may  be  warmed  to  40°  C.  whereby  the  reaction  is  accelerated. 

When  the  iron-solution  is  dilute,  the  reaction  proceeds  with  incon- 
venient slowness,  but  after  some  practice  the  results  are  good.  From 
the  number  of  c.  c.  of  the  hyposulphite  solution  required  to  reduce  a 
known  quantity  of  sesquioxide  of  iron,  taking  the  mean  of  a number  of 
nearly  accordant  observations,  may  be  calculated  the  quantity  of  sesqui- 
oxide of  iron,  or  of  metallic  iron,  corresponding  to  1 c.  c.  of  hyposulphite, 
and  this  factor,  multiplied  into  the  number  of  c.  c.  consumed  in  any 
analysis,  gives  the  quantity  of  sesquioxide  of  iron  or  of  metallic  iron 
sought. 

The  solution  of  the  iron  which  it  is  desired  to  estimate  is  conducted 
as  described  for  making  the  standard  b.  It  must  be  free  from  nitric 
acid  and  oxides  of  chlorine ; should  be  kept  rather  concentrated,  as  a 
matter  of  convenience  for  rapid  working,  and  should  contain  a moderate 
amount  of  free  hydrochloric  acid.  The  analysis  is  conducted  as  just 
described  for  the  standardizing. 

The  solution  of  hyposulphite  alters  slowly  with  deposition  of  sulphur, 
and  its  value  must  be  determined  anew  every  week  or  two. 

The  process  is  convenient  and  excellent,  though  not  so  good  for  the 
estimation  of  minute  quantities  of  iron  as  the  method  with  permanganate.] 


i§  H4,  ns.] 


SESQUIOXIDE  OF  URANIUM. 


205 


§ 114. 

Supplement  to  the  Fourth  Group. 

7.  Sesquioxide  of  Uranium. 

If  the  compound  in  which  the  sesquioxide  of  uranium  is  to  be  deter- 
mined contains  no  other  fixed  substances,  it  may  often  be  converted  into 
protosesquioxide  (Ur  O,  Ur2  03)  by  simple  ignition.  If  sulphuric  acid 
is  present,  small  portions  of  carbonate  of  ammonia  must  be  thrown  into 
the  crucible  towards  the  end  of  the  operation. 

In  cases  where  the  application  of  this  method  is  inadmissible,  the  solu- 
tion of  uranium  (which,  if  it  contains  protoxide,  must  first  be  warmed 
with  nitric  acid,  until  the  protoxide  is  converted  into  sesquioxide)  is 
precipitated  with  ammonia.  The  yellow  precipitate  formed,  which  con- 
sists of  hydrated  ammonio-sesquioxide  of  uranium , is  washed  with  a 
dilute  solution  of  chloride  of  ammonium,  to  prevent  the  fluid  passing 
milky  through  the  filter.  The  precipitate  is  dried  and  ignited  (§  53). 
To  make  quite  sure  of  obtaining  the  protosesquioxide  in  the  pure  state, 
the  crucible  is  ignited  for  some  time  in  a slanting  position  and  uncovered ; 
the  lid  is  then  put  on,  while  the  ignition  is  still  continuing ; the  cruci- 
ble is  allowed  to  cool  under  the  desiccator,  and  weighed  (H.  Rose). 

If  the  solution  from  which  the  sesquioxide  of  uranium  is  to  be  pre- 
cipitated contains  other  bases  (alkaline  earths,  or  even  alkalies),  portions 
of  these  will  precipitate  along  with  the  ammonio-sesquioxide  of  uranium. 
For  the  measures  to  be  resorted  to  in  such  cases,  1 refer  to  Section  Y. 

The  reduction  of  the  protosesquioxide  of  uranium  to  the  state  of 
protoxide  (Ur  O)  is  an  excellent  means  of  ascertaining  its  purity  for  the 
purpose  of  control.  This  reduction  is  effected  by  ignition  in  a current 
of  hydrogen  gas,  in  the  way  described  § 111,  1 (Cobalt).  By  intense 
ignition,  the  property  of  the  protoxide  of  uranium  to  ignite  in  the  air  is 
destroyed.  The  separation  of  sesquioxide  of  uranium  from  phosphoric 
acid  is  effected  by  fusing  the  compound  with  cyanide  of  potassium  and 
carbonate  of  soda.  Upon  extracting  the  fused  mass  with  water,  the 
phosphoric  acid  is  obtained  in  solution,  wdiilst  the  uranium  is  left  as 
protoxide.  . Knop  and  Arendt  * have  employed  this  method. 

The  equivalent  of  protosesquioxide  of  uranium  = 210*2,  viz.,  178*2  of 
uranium  and  32  of  oxygen.  In  100  parts,  the  compound  consists  of 
84’77  of  uranium  and  15*23  of  oxygen.  The  equivalent  of  protoxide 
of  uranium  is  67*4,  viz.,  59*4  of  uranium  and  8 of  oxygen  ; in  100 
parts,  the  protoxide  consists  of  88*13  of  uranium  and  11*87  of 
oxygen. 

FIFTH  GROUP. 

OXIDE  OF  SILVER — OXIDE  OF  LEAD SUEOXIDE  OF  MERCURY OXIDE  OF 

MERCURY OXIDE  OF  COPPER TEROXIDE  OF  BISMUTH OXIDE  OF  CAD- 
MIUM  (protoxide  OF  palladium). 

§ 115‘ 

1.  Oxide  of  Silver. 

a.  Solution. 

Metallic  silver,  and  those  of  its  compounds  which  are  insoluble  in 
water  are  best  dissolved  in  nitric  acid  (if  soluble  in  that  acid).  Dilute 
nitric  acid  suffices  for  most  compounds  ; sulphide  of  silver,  however,  re- 


* Chem.  Centralbl.  1856,  773. 


206 


DETERMINATION. 


[§  H5. 


quires  concentrated  acid.  The  solution  is  effected  best  in  a flask.  Chlo- 
ride, bromide,  and  iodide  of  silver  are  insoluble  in  water  and  in  nitric 
acid.  To  get  the  silver  contained  in  them  in  solution,  proceed  as  fol- 
lows : — fuse  the  salt  in  a porcelain  crucible  (this  operation,  though 
not  absolutely  indispensable,  had  better  not  be  omitted),  pour  water 
over  it,  put  a piece  of  clean  zinc  or  iron  upon  it,  and  add  some  dilute 
sulphuric  acid.  Wash  the  reduced  spongy  silver,  first  with  dilute  sul- 
phuric acid,  then  with  water,  and  finally  dissolve  it  in  nitric  acid.  How- 
ever, as  we  shall  see  below,  the  quantitative  analysis  of  these  salts  does 
not  necessarily  involve  their  solution. 

b.  Determination. 

Silver  may  be  weighed  as  chloride , sulphide , or  cyanide , or  in  the 
metallic  state  (§  82).  It  is  also  frequently  determined  by  volumetric 
analysis. 

We  may  convert  into 

1.  Chloride  of  Silver. 

All  compounds  of  silver  without  exception. 

2.  Sulphide  of  Silver.  3.  Cyanide  of  Silver. 

All  compounds  soluble  in  water  or  nitric  acid. 

4.  Metallic  Silver. 

Oxide  of  silver,  and  some  of  its  compounds  with  readily  volatile  acids ; 
salts  of  silver  with  organic  acids ; chloride,  bromide,  iodide,  and  sulphide 
of  silver. 

The  method  4 is  the  most  convenient,  and  is  preferred  to  the  others  in 
all  cases  where  its  application  is  admissible.  The  method  1 is  that 
most  generally  resorted  to.  2 and  3 serve  mostly  only  to  effect  the 
separation  of  oxide  of  silver  from  other  bases. 

In  assays  for  the  Mint,  silver  is  usually  determined  volumetrically  by 
Gay-Lussac’s  method.  Pisani’s  volumetric  method  is  especially  suited 
to  the  determination  of  very  small  quantities  of  silver.  The  estimation 
of  silver  by  cupellation  will  be  described  in  the  Special  Part. 

1.  Determination  of  Silver  as  Chloride, 
a.  In  the  Wet  Way. 

The  precipitated  chloride  of  silver  may  be  separated  from  the  super- 
natant fluid  either  by  decantation  or  by  filtration  ; the  former  is  gene- 
rally preferred  for  large  quantities  of  precipitate,  the  latter  answers 
better  for  small  quantities.  Whichever  process  is  adopted,  the  chloride 
of  silver  must  be  completely  protected  from  the  influence  of  direct  sun- 
light, and  even  the  action  of  diffused  daylight  must  be  as  far  as  possible 
avoided. 

a.  Determination  by  Decantation. 

The  moderately  dilute  silver-solution  is  introduced  into  a tall  flask 
with  long  neck  and  narrow  mouth,  and  some  nitric  acid  added  to  it ; the 
fluid  is  heated  to  about  60°,  and  hydrochloric  acid  carefully  added  in 
such  quantity,  that  some  silver  still  remains  unprecipitated,  and  the 
chloride  separates  in  consequence  in  large  flocks.  After  their  formation 
has  been  completed  by  gently  moving  the  fluid,  add  cautiously  move 
hydrochloric  acid,  till  the  last  drops  give  no  further  precipitate  (a  con- 
siderable excess  should  be  avoided,  as  hydrochloric  acid  dissolves  very 
small  traces  of  chloride  of  silver).  The  mouth  of  the  flask  is  thei£ 


§ 115.] 


OXIDE  OF  SILVER. 


207 


closed  with  a perfectly  smooth  cork  (or,  better  still,  with  a well-ground 
glass  stopper),  and  the  flask  vigorously  shaken  until  the  precipitated 
chloride  of  silver  has  united  into  coherent  lumps,  and  the  supernatant 
fluid  has  become  pretty  clear.  The  chloride  adhering  to  the  neck  of 
the  flask  is  then  removed  by  agitating  the  clear  fluid,  and  t)ie  last  traces 
are  washed  down  by  means  of  a wash-bottle  ; the  flask  is  then  allowed 
to  stand  at  rest  for  twelve  hours  in  a dark  place  at  the  ordinary  tem- 
perature. At  the  end  of  this  time  the  precipitate  will  have  completely 
subsided  and  the  fluid  will  be  clear.  The  latter  is  then  slowly  and  cau- 
tiously decanted,  as  far  as  practicable,  into  a beaker,  so  as  to  retain 
every  particle  of  the  chloride  in  the  flask,  whence  it  is  carefully  trans- 
ferred to  an  upright  smooth  porcelain  crucible  that  has  been  weighed  : 
the  last  particles  of  chloride  of  silver  are  got  out  by  putting  a little 
water  in  the  flask,  closing  the  mouth  with  the  finger,  inverting,  and 
rinsing  the  sides  and  bottom  by  agitation.  The  particles  thus  collect 
in  the  neck,  and  can  easily  be  transferred  to  the  crucible,  by  holding 
the  mouth  of  the  flask  close  over  the  latter,  and  letting  the  fluid  run 
out ; a washing  bottle  with  the  jet  turned  upwards  (§  46)  may  also  be 
used  with  advantage. 

When  the  chloride  of  silver  has  completely  subsided  in  the  crucible, 
which  is  greatly  accelerated  by  exposure  to  the  heat  of  a water-bath,  the 
clear  supernatant  fluid  is  carefully  decanted  down  a glass  rod  into  the 
same  beaker  which  contains  the  liquid  of  the  first  decantation.  The 
chloride  of  silver  in  the  crucible  is  moistened  with  a few  drops  of  nitric 
acid,  and  then  treated  with  hot  distilled  water  ; the  chloride  is  again  al- 
lowed to  subside,  the  clear  supernatant  fluid  again  decanted,  and  the 
same  operation  repeated  until  a drop  of  the  last  decanted  fluid  no  longer 
gives  the  slightest  turbidity  with  nitrate  of  silver.  The  supernatant 
fluid  is  then  removed  as  completely  as  possible  by  means  of  a pipette,  or 
by  cautious  decantation ; the  chloride  is  thoroughly  dried  on  the  water- 
batli,  and  subsequently  heated  to  incipient  fusion  over  the  lamp,  taking 
care  to  apply  a very  gentle  heat  at  first  ; as  soon  as  the  chloride  begins 
to  fuse  round  the  border,  the  crucible  is  allowed  to  cool,  and  weighed. 

To  remove  the  mass  from  the  crucible,  completely  and  without  injury 
to  the  latter,  a piece  of  iron  or  zinc  is  placed  upon  the  chloride,  and 
highly  dilute  hydrochloric  or  sulphuric  acid  added.  The  crucible  is  finally 
cleansed,  dried,  and  weighed,  if  this  has  not  been  done  before  the  opera- 
tion. Should  the  liquids  successively  decanted  from  the  chloride  of  silver 
not  be  perfectly  clear  and  transparent,  they  are  kept  standing  in  the 
cold  until  the  last  particles  of  chloride  have  completely  subsided,  which 
frequently  requires  many  hours ; .the  clear  supernatant  fluid  is  then  de- 
canted, and  the  deposited  chloride  added  to  the  bulk  of  the  precipitate 
in  the  crucible,  the  whole  washed  and  treated  as  above  ; or — and  this  is 
a more  expeditious  way — the  minute  quantity  of  chloride  is  collected  on  a 
small  filter,  treated  as  directed  in  /3,  and  added  to  the  principal  amount. 

[3.  Determination  by  Filtration. 

The  chloride  of  silver  is  precipitated  and  allowed  to  subside  as  in  a ; 
the  supernatant  fluid  is  then  passed  through  a small  filter,  to  which  the 
precipitate  is  subsequently  transferred,  with  the  aid  of  a little  hot  water 
acidulated  with  nitric  acid ; the  precipitate  collected  on  the  filter  is 
washed,  first  with  water  acidulated  with  nitric  acid,  afterwards  with 
pure  water ; it  is  then  thoroughly  dried,  the  contents  of  the  filter  are 
transferred  as  completely  as  possible  to  a small  porcelain  crucible,  and 


208 


DETERMINATION. 


L§  115- 


the  filter  itself  is  burnt  on  the  lid.  In  this  operation  some  of  the  chlo- 
ride is  always  reduced,  the  ash  is  therefore  added  to  the  chloride  in  the 
crucible,  together  with  two  or  three  drops  of  dilute  nitric  acid : heat  is 
applied  for  a short  time,  and  then  a drop  or  two  of  hydrochloric  acid  add- 
id  ; lastly  heat,  at  first  gently  till  dry,  then  to  incipient  fusion,  and  weigh. 

For  the  properties  of  the  precipitate,  see  § 82.  Both  methods  give 
very  accurate  results,  unless  large  quantities  of  such  salts  are  present  as 
have  the  property  of  slightly  dissolving  chloride  of  silver,  compare  § 82. 
In  order  to  be  quite  safe  in  this  connection  it  is  advisable  to  test  the  clear 
filtrate  with  sulphuretted  hydrogen  before  throwing  it  away. 

b.  In  the  Dry  Way. 

This  method  serves  more  exclusively  for  the  analysis  of  bromide  and 
iodide  of  silver,  although  it  can  be  applied  in  the  case  of  other  com- 
pounds. 

The  process  is  conducted  in  the  apparatus  illustrated  by  Fig.  49, 
leaving  off  the  tubes  E and  F,  and  employing  a straight  bulb-tube  or  a 
plain  tube  with  porcelain  tray  instead  of  the  bent  tube  D. 


Fig.  49. 


A is  an  apparatus  for  disengaging  chlorine ; B contains  concentrated 
sulphuric  acid,  C chloride  of  calcium ; D is  a bulb-tube  intended  for  the 
reception  of  the  iodide  or  bromide  of  silver  ; and  G,  which  directly  is  con- 
nected with  D,  serves  to  conduct  the  chlorine  gas  into  the  open  air  or 
into  milk  of  lime.  The  operation  is  commenced  by  introducing  the 
compound  to  be  analyzed  into  the  bulb,  and  applying  heat  to  the  latter 
until  its  contents  are  fused  ; when  cold,  the  tube  is  weighed  and  connected 
with  the  apparatus.  Chlorine  gas  is  then  evolved  from  A ; when  the 
evolution  of  the  gas  has  proceeded  for  some  time,  the  contents  of  the 
bulb  are  heated  to  fusion,  and  kept  in  this  state  for  about  fifteen  mi- 
nutes, agitating  now  and  then  the  fused  mass.  The  bulb-tube  is  then 
removed  from  the  apparatus,  allowed  to  cool,  and  held  in  a slanting  po- 
sition to  replace  the  chlorine  by  atmospheric  air ; it  is  subsequently 
weighed,  then  again  connected  with  the  apparatus,  and  the  former  pro- 


OXIDE  OF  SILVER. 


209 


§ 115.1 

cess  repeated,  keeping  the  contents  of  D in  a state  of  fusion  for  a few 
minutes.  The  operation  may,  in  ordinary  cases,  be  considered  con- 
cluded if  the  weight  of  the  tube  suffers  no  variation  by  the  repetition  of 
the  process.  If  the  highest  degree  of  accuracy  is  to  be  attained,  heat 
the  chloride  of  silver  again  to  fusion,  passing  at  the  same  time  a slow 
stream  of  pure,  dry  carbonic  acid  through  the  tube,  in  order  to  drive 
out  the  traces  of  chlorine  absorbed  by  the  fused  chloride.  Allow  to 
cool,  hold  obliquely  for  a short  time,  so  as  to  replace  the  carbonic  acid 
by  air,  and  finally  weigh.  See  § 82. 

2.  Determination  as  Sulphide  of  Silver. 

Sulphuretted  hydrogen  precipitates  silver  conpletely  from  acid,  neu- 
tral, and  alkaline  solutions  ; sulphide  of  ammonium  precipitates  it  from 
neutral  and  alkaline  solutions.  Recently  prepared  perfectly  clear  solu- 
tion of  sulphuretted  hydrogen  may  be  employed  to  precipitate  small 
quantities  of  silver ; to  precipitate  larger  quantities,  the  solution  of  the 
salt  of  silver  (which  must  not  be  too  acid)  is  moderately  diluted,  and 
washed  sulphuretted  hydrogen  gas  conducted  into  it.  After  complete 
precipitation  has  been  effected,  and  the  sulphide  of  silver  has  perfectly 
subsided  (with  exclusion  of  air),  it  is  collected  on  a weighed  filter, 
washed,  dried  at  100°  and  weighed.  For  the  properties  of  the  preci- 
pitate, see  § 82.  This  method,  if  properly  executed,  gives  very  accurate 
results.  The  operator  must  take  care  to  filter  quickly,  and  to  prevent 
the  access  of  air  as  much  as  possible  during  the  filtration,  since,  if  this 
precaution  be  neglected,  sulphur  is  likely  to  separate  from  the  sulphuretted 
hydrogen  water,  which,  of  course,  would  add  falsely  to  the  weight  of 
the  sulphide  of  silver. 

The  sulphide  of  silver  must,  however,  never  be  weighed  as  just 
described,  unless  the  analyst  is  satisfied  that  no  sulphur  has  fallen  down 
with  it,  as  would  occur  if  the  fluid  contained  hvponitric  acid,  sesqui- 
oxide  of  iron,  or  any  other  substance  which  decomposes  sulphuretted 
hydrogen.  In  case  the  precipitate  does  contain  admixed  sulphur, 
the  simplest  process  is  to  convert  it  into  metallic  silver  (H.  Rose  *). 
For  this  purpose  it  is  transferred  to  a weighed  porcelain  crucible,  the 
filter  ash  is  added,  and  the  whole  is  heated  to  redness  in  a sti  earn  of 
hydrogen,  the  apparatus  described  in  § 108  being  employed.  Results 
accurate. 

Should  the  apparatus  in  question  not  be  at  the  operator’s  disposal,  he 
may,  after  complete  washing  of  the  precipitate,  carefully  rinse  it  into  a 
porcelain  dish  (without  injuring  the  weighed  filter),  heat  it  once  or  twice 
with  a moderately  strong  solution  of  pure  sulphite  of  soda,  re-transfer 
the  precipitate  (now  freed  from  admixed  sulphur)  to  the  old  filter,  wash 
well,  dry  and  weigh  (J.  Lowe  f ) ; or  he  may  treat  the  dried  precipitate, 
together  with  the  filter-ash,  with  moderately  dilute  chlorine-free  nitric 
acid  at  a gentle  heat,  till  complete  decomposition  has  been  effected  (till 
the  undissolved  sulphur  has  a clean  yellow  appearance),  filter,,  wash  well, 
and  proceed  according  to  1. 

3.  Determination  as  Cyanide  of  Silver. 

Mix  the  neutral  or  acid  solution  of  silver  with  cyanide  of  potassium, 
until  the  precipitate  of  cyanide  of  silver  which  forms  at  first  is  redissolved  ; 
add  nitric  acid  in  slight  excess,  and  apply  a gentle  heat.  After  some 

* Fogg.  Anna!  110,  139. 

Id 


f Joum.  f.  prakt.  Chem.  77,  73'. 


210 


DETERMINATION. 


L§  H5. 


time,  collect  the  precipitated  cyanide  of  silver  on  a weighed  filter,  wash, 
dry  at  100°,  and  weigh.  For  the  properties  of  the  precipitate,  see  § 82. 
The  results  are  accurate. 

4.  Determination  as  Metallic  Silver. 

Oxide  of  silver,  carbonate  of  silver,  &c.,  are  easily  reduced  by  simple 
ignition  in  a porcelain  crucible.  In  the  reduction  of  salts  of  silver  with 
organic  acids,  the  crucible  is  kept  covered  at  first,  and  a moderate  heat 
applied ; after  a time  the  lid  is  removed,  and  the  heat  increased,  until 
the  whole  of  the  carbon  is  consumed.  For  the  properties  of  the  residue, 
see  § 82.  The  results  are  absolutely  accurate,  except  as  regards  salts  of 
silver  with  organic  acids;  in  the  analysis  of  the  latter,  it  not  unfre- 
quently  happens  that  the  reduced  silver  contains  a minute  portion  of 
carbon,  which  increases  the  weight  of  the  residue  to  a trifling  extent. 

If  it  is  desired  to  transform  chloride,  bromide,  iodide,  or  sulphide  of 
silver  into  metallic  silver,  for  the  purpose  of  analysis,  they  are  heated 
in  a current  of  pure  dry  hydrogen  to  redness,  till  the  weight  remains  con- 
stant. The  process  may  be  conducted  in  a porcelain  crucible  or  a bulb- 
tube.  In  the  former  case,  the  apparatus  described  § 108,  fig.  No.  47 
is  used ; in  the  latter  the  apparatus  represented  p.  208,  with  the 
substitution,  of  course,  of  hydrogen  for  chlorine.  If  the  bulb-tube  is  used, 
it  must,  after  cooling  and  before  being  weighed,  be  held  in  an  inclined 
position,  so  that  the  hydrogen  may  be  replaced  by  air.  The  results 
are  perfectly  accurate.  See  also  Cupellation,  Special  Part. 

5.  Volumetric  Methods. 

1.  Gay-Lussac’s. 

This,  the  most  exact  of  all  known  volumetric  processes,  was  intro- 
duced by  Gay-Lussac  as  a substitute  for  the  assay  of  silver  by  cupella- 
tion, was  thoroughly  investigated  by  him,  and  will  be  found  fully  de- 
scribed in  his  work  on  the  subject.  This  method  has  been  rendered  still 
more  precise  by  the  researches  of  G.  J.  Mulder,  to  whose  exhaustive  mo- 
nograph * 1 refer  the  special  student  of  this  branch.  I shall  here  con- 
fine myself  to  giving  the  process  so  far  as  to  suit  the  requirements  of 
the  chemical  laboratory,  taking  only  for  granted  that  the  analyst  has  the 
ordinary  measuring  apparatus,  &c.,  at  his  disposal.  Mulder’s  results 
will  be  made  use  of  to  the  full  extent  possible  under  these  circumstances. 

a.  Requisites. 

a..  Solution  of  chloride  of  sodium. 

Take  chemically  pure  chloride  of  sodium — either  artificially  prepared 
or  pure  rock-salt — powder  it  roughly  and  ignite  moderately  (not  to 
fusion  j-).. 

Now  dissolve  5*4145  grm.  in  distilled  water  to  1 litre,  measured  at  16°. 
100  c.  c.  of  this  solution  contains  a quantity  of  chloride  of  sodium, 
equivalent  to  1 grm.  of  silver. 

The  solution  is  kept  in  a stoppered  bottle  and  shaken  before  use. 

j3.  Decimal  solution  of  chloride  of  sodium. 

Transfer  50  c.  c.  of  the  solution  described  in  a to  a 500  c.  c.  measur- 

* Die  Silberprobirmethode  (see  note,  p.  122). 

f On  fusion,  if  the  flame  can  in  the  least  way  act  upon  it,  it  takes  an  alkaline 
reaction,  since  under  the  influence  of  vapor  of  water  and  carbonic  acid,  a little 
hydrochloric  acid  is  formed  and  escapes,  while  a corresponding  quantity  of  car- 
bonate of  soda  remains . 


OXIDE  OF  SILVER. 


211 


§ 115.] 

in g flask,  fill  up  to  tlie  mark  with  distilled  water  and  shake.  Each  c.  c. 
of  this  decimal  solution  corresponds  to  0*001  grm.  silver.  The  measuring 
must  be  performed  at  16°. 

The  solution  is  kept  as  the  other. 

y.  Decimal  silver  solution. 

Dissolve  0*5  grm.  chemically  pure  silver  in  2 to  3 c.  c.  pure  nitric 
acid  of  1*2  sp.  gr.,  and  dilute  the  solution  with  water  exactly  to  500 
c.  c.  measured  at  16°,  Each  c.  c.  contains  0*001  grm.  silver.  The  so- 
lution is  kept  in  a stoppered  bottle  and  protected  against  the  influence 
of  light. 

d.  Test-bottles. 

These  should  be  of  white  glass,  holding  easily  200  c.  c.,  closed  with 
well-ground  glass  stoppers,  running  to  a point  below.  The  bottles  fit 
into  cases  blackened  on  the  inside,  and  reaching  up  to  their  necks.  In 
order  to  protect  the  latter  also  from  the  action  of  light,  a black-cloth 
cover  is  employed. 

b.  Principle. 

Suppose  we  know  the  value  of  a solution  of  chloride  of  sodium,  i.e.,  the 
quantity  that  is  necessary  to  precipitate  a given  amount  of  silver,  say 
1 grm.,  we  are  in  the  position,  with  the  aid  of  this  solution,  to  deter- 
mine an  unknown  amount  of  silver,  for  if  we  put  x for  the  unknown 
amount  of  silver,  then 

c.  c.  of  solution  used  for  1 grm.  : c.  c.  used  for  x y.  1 grm.  : x. 

But  if  we  examine  whether  1 eq.  chloride  of  sodium  dissolved  in  water 
actually  precipitates  1 eq.  of  silver  dissolved  in  iiitric  acid  exactly,  we 
find  that  this  is  not  the  case.  On  the  contrary,  the  clear  supernatant 
fluid  gives  a small  precipitate  both  on  the  addition  of  a little  solution 
of  chloride  of  sodium,  and  on  the  addition  of  a little  silver-solution,  as 
Mulder  has  most  accurately  determined.  The  value  of  a solution  of 
chloride  of  sodium  in  the  sense  explained  above  cannot,  therefore,  be 
reckoned  from  the  amount  of  salt  it  contains,  by  calculating  1 eq.  silver 
for  1 eq.  chloride  of  sodium,  but  it  can  only  be  obtained  by  experiment. 
Mulder  has  shown,  that  the  temperature  and  the  degree  of  dilution 
have  some  influence,  and  also  that  this  fact  is  to  be  explained  on  the 
ground  of  the  solvent  power  of  the  nitrate  of  soda  produced  on  the 
chloride  of  silver.  In  the  solution  thus  formed  we  have  to  imagine  Na 
O,  H 05  and  1ST  a Cl  with  Ag  O,  N 05  in  a certain  state  of  equilibrium, 
which,  on  the  addition  of  either  Ha  Cl  or  Ag  O,  H 05  is  destroyed, 
chloride  of  silver  being  precipitated. 

From  this  interesting  observation  it  follows,  that  if  to  a silver-solution 
we  add  at  first  concentrated  solution  of  chloride  of  sodium,  then  deci- 
mal solution  drop  by  drop,  till  the  exact  point  is  reached  when  no  more 
precipitate  appears,  now,  on  addition  of  decimal  silver-solution  a small 
precipitate  will  be  again  produced  ; and  if  we  add  the  latter  drop  by  drop, 
till  the  last  drop  occasions  no  turbidity,  then  again  decimal  solution  of 
chloride  of  sodium  will  give  a small  precipitate.  On  noticing  the  num- 
ber of  drops  of  both  decimal  solutions  which  are  required  to  pass  from 
one  limit  to  the  other,  we  find  that  the  same  number  of  each  are  used. 
Let  us  suppose  that  we  had  added  decimal  solution  of  chloride  of  sodium 
till  it  ceased  to  react,  and  had  then  used  20  drops*  of  decimal  silver-solution, 

* Twenty  drops  from  Mulder’s  dropping  apparatus  are  equal  to  1 c.  c . 


212 


DETERMINATION. 


till  this  ceased  to  produce  a further  turbidity,  we  must  now  again  add 
20  drops  of  decimal  solution  of  chloride  of  sodium,  in  order  to  reach  the 
point  at  which  this  ceases  to  react.  Were  we  to  add  only  10  instead  of 
these  20  drops,  we  have  the  neutral  point,  as  Mulder  calls  it,  i.e .,  the 
point  at  which  both  silver  and  chloride  of  sodium  produce  equal  pre- 
cipitates. 

We  have,  therefore,  3 different  points  to  choose  from  for  our  final 
reaction  : a , the  point  at  which  chloride  of  sodium  has  just  ceased  to 
precipitate  the  silver ; b , the  neutral  point ; c,  the  point  at  which  silver 
solution  has  just  ceased  to  precipitate  chloride  of  sodium.  Whichever 
we  may  choose,  we  must  keep  to  it,  i.e.,  we  must  not  use  a different  point 
in  standardizing  the  chloride  of  sodium  solution  and  in  performing  an 
analysis.  The  difference  obtained  by  using  first  a and  then  b is,  ac- 
cording to  Mulder,  for  1 grm.  silver,  at  16°,  about  0*5  mgrm.  silver  ; by 
employing  first  a and  then  c,  as  was  permitted  in  the  original  process  of 
Gay-Lussac,  the  difference  is  increased  to  1 mgrm. 

For  our  object,  it  appears  most  convenient  to  consider,  once  for  all, 
the  point  a as  the  end,  and  never  to  finish  with  the  silver-solution.  If 
the  point  has  been  overstepped  by  the  addition  of  too  large  an  amount 
of  decimal  solution  of  chloride  of  sodium,  2 or  3 c.  c.  of  decimal  silver- 
solution  should  be  added  all  at  once.  The  end-point  is  then  found 
by  carefully  adding  decimal  solution  of  chloride  of  sodium  again, 
and  the  quantity  of  silver  in  the  silver-solution  added  is  reckoned 
from  the  original  amount  of  silver  weighed  in  making  the  solution. 

c.  Performance  of  the  Process. 

This  is  divided  into  two  operations — a,  the  fixing  of  the  value  of  the 
chloride  of  sodium  solution  ; j 3,  the  assay  of  the  silver  alloy  to  be 
examined. 

a.  Determination  of  the  value  of  the  Chloride  of  Sodium  solu- 
tion, i.e.,  its  power  of  precipitating  silver. 

Weigh  off  exactly  from  1*001  to  1*003  grm.  chemically  pure  silver, 
put  it  into  a test-bottle,  add  5 c.  c.  perfectly  pure  nitric  acid,  of  1*2  sp. 
gr.,  and  heat  the  bottle  in  an  inclined  position  in  a water- or  sand-bath 
till  complete  solution  is  effected.  Now  blow  out  the  nitrous  fumes 
from  the  upper  part  of  the  bottle,  and  after  it  has  cooled  a little,  place 
it  in  a stream  of  water,  the  temperature  of  which  is  about  16°,  and  let 
it  remain  there  till  its  contents  are  cooled  to  this  degre3;  wipe  it  dry, 
and  place  it  in  its  case. 

Now  fill  the  100  c.  c.  pipette  with  the  concentrated  solution  of  chlo- 
ride of  sodium,  which  is  then  allowed  to  flow  into  the  test-bottle  con- 
taining the  silver  solution.*  Insert  the  glass  stopper  firmly  (after 
moistening  it  with  water),  cover  the  neck  of  the  bottle  with  the  cap  of 
black  stuff  belonging  to  it,  and  shake  violently,  without  delay,  till  the 
chloride  of  silver  settles,  leaving  the  fluid  perfectly  clear.  Then  take 
the  stopper  out,  rub  it  on  the  neck,  so  as  to  remove  all  chloride  of  sil- 
ver, replace  it  firmly,  and  by  giving  the  bottle  a few  dexterous  turns, 
rinse  the  chloride  down  from  the  upper  part.  After  allowing  to  rest  a 
little,  again  remove  the  stopper,  and  add,  from  a burette  divided  into 
-jig-  c.  c.,  decimal  chloride  of  sodium  solution,  allowing  the  drops  to  fall 

* The  pipette,  having  been  filled  above  the  mark,  should  be  fixed  in  a support 
before  the  excess  is  allowed  to  run  out,  otherwise  the  measuring  will  not  be  suf- 
ficiently accurate. 


§ US.] 


OXIDE  OF  SILVER. 


213 


against  the  lower  part  of  the  neck,  the  bottle  being  held  in  an  inclined 
position.  If,  as  above  directed,  1*001  to  1*003  grm.  silver  have  been 
employed,  the  portions  of  chloride  of  sodium  solution  at  first  added 
may  be  c.  c.  After  each  addition,  raise  the  bottle  a little  out  of  its 
case,  observe  the  amount  of  precipitate  produced,  shake  till  the  fluid 
has  become  clear  again,  and  proceed  as  above,  before  adding  each  fresh 
quantity  of  chloride  of  sodium  solution.  The  smaller  the  precipitate 
produced,  the  smaller  should  be  the  quantity  of  chloride  of  sodium  next 
added ; towards  the  end  only  two  drops  should  be  added  each  time ; and 
quite  at  the  end  read  oft*  the  height  of  the  fluid  in  the  burette  before 
each  further  addition.  When  the  last  two  drops  give  no  more  preci- 
pitate, the  previous  reading  is  the  correct  one. 

If  by  chance  the  point  has  been  overstepped,  and  the  time  has  been 
missed  for  the  proper  reading  off  of  the  burette,  add  2 to  3 c.  c.  of  the 
decimal  silver  solution  (the  silver  in  which  is  to  be  added  to  the  quantity 
first  weighed),  and  try  again  to  hit  the  point  exactly  by  careful  addition 
of  decimal  chloride  of  sodium  solution. 

The  value  of  the  chloride  of  sodium  solution  is' now  known.  Reckon 
it  to  1 grm.  silver. 

Suppose  we  had  used  for  1*002  grm.  silver  100  c.  c.  of  concentrated  and 
3 c.  c.  of  decimal  chloride  of  sodium  solution ; this  makes  altogether  100*3 
of  concentrated ; then 

1*002  : 1*000  ::  100*3  : a 

a = 100*0998 

We  may  without  scruple  put  100*1  for  this  number.  We  now  know  that 
100*1  c.  c.  of  the  concentrated  solution  of  chloride  of  sodium,  measured 
at  16°,  exactly  precipitates  1 grm.  of  silver.  This  relationship  serves  as 
the  foundation  of  the  calculation  in  actual  assaying,  and  must  be  re- 
examined whenever  there  is  reason  to  imagine  that  the  strength  of  the 
chloride  of  sodium  solution  may  have  altered. 

0.  The  actual  assay  of  the  Silver-Alloy. 

Weigh  off  so  much  as  contains  about  1 grm.  of  silver,  or  better,  a few 
mgrm.  more ; * dissolve  in  a test-bottle  in  5 to  7 c.  c.  nitric  acid,  and 
proceed  in  all  respects  exactly  as  in  a. 

Suppose  we  had  taken  1*116  grm.  of  the  alloy,  and,  in  addition  to  the 
100  c.  c.  of  concentrated  chloride  of  sodium  solution,  had  used  5 c.  c.  of 
the  dilute  ( = 0*5  concentrated),  how  much  silver  would  the  alloy 
contain  ? 

Presuming  that  we  use  the  same  chloride  of  sodium  solution  which 
served  as  our  example  in  a,  100*1  c.  c.  of  which  = 1 grm.  silver,  then 

100*1  : 100*5  : : 1*000  : a 

a = 1*003996  (say  1*004). 


* In  coins,  which  consist  of  9 parts  of  silver  and  1 part  of  copper,  therefore  take 
about  t *115  or  1*120.  In  weighing  off  alloys  of  silver  and  copper,  which  do  not  cor- 
respond to  the  formula  Ag3  Cu4  (standard  =iiJooo1  S we  must  remember  that  they 
are  never  homogeneous  in  the  mass  ; thus,  for  instance,  the  pieces  of  metal  from 
which  coins  are  stamped,  often  show  1 *5  to  1 *7  in  a thousand  more  silver  in  the 
middle  than  at  the  edges.  In  assaying  alloys,  then,  portions  from  various  parts 
of  the  mass  must  be  taken,  in  order  to  get  a correct  result  The  inaccuracy,  how- 
ever, proceeding  from  the  cause  above  mentioned,  can  only  be  completely  over- 
come by  fusing  the  alloy,  and  taking  out  a portion  from  the  well-stirred  mass  for 
the  assay. 


214 


DETERMINATION. 


[§  ^ 


We  may  also  arrive  at  the  same  result  in  the  following  manner  : — 

Na  Cl  Solution. 

For  the  precipitation  of  the  silver  in  the  alloy  were  used  100*5  c.  c. 


For  1 grm.  silver  are  necessary 100*1  c.  c. 

Difference 0*4  c.  c. 


There  are,  therefore,  4 mgrm.  of  silver  present  more  than  a grm.,  on 
the  presumption  that  0*1  of  the  concentrated  chloride  of  sodium  solution 
(=1  c.  c.  of  the  decimal  solution)  corresponds  to  1 mgrm.  silver.  This 
supposition,  although  not  absolutely  correct,  may  be  safely  made,  for 
the  inexactness  it  involves  is  too  minute,  as  is  evident  from  the  previous 
calculation. 

Before  we  can  execute  this  process  exactly,  we  must  know  the  quantity 
of  silver  the  alloy  contains  very  approximately.  In  assaying  coins  of 
known  value  this  is  the  case,  but  with  other  silver  alloys  it  is  usually 
not  so.  Under  the  latter  circumstances  an  approximate  estimation  must 
precede  the  regular  assay.  This  is  performed  by  weighing  off  ^ grm.  (or 
in  the  case  of  alloys  that  are  poor  in  silver,  1 grm.),  dissolving  in  3 to 
6 c.  c.  nitric  acid,  and  adding  from  the  burette  chloride  of  sodium  solution, 
— first  in  larger,  then  in  smaller  quantities — till  the  last  drops  produce  no 
further  turbidity.  The  last  drops  are  not  reckoned  with  the  rest.  The 
operation  is  conducted,  as  regards  shaking,  &c.,  as  previously  given. 
Suppose  we  had  weighed  off  0*5  grm.  of  the  alloy,  and  employed  25  c.  c. 
of  the  chloride  of  sodium  solution — taking  the  above  supposed  value  of 
the  latter — 

We  have  100*1  : 25  : : 1*000  : a? 

x = 0*2497 

that  is,  the  silver  in  *5  grm.  of  the  alloy ; and  as  to  the  quantity  of  alloy 
we  have  to  weigh  oft*  for  the  assay  proper, 

We  have  *2497  : 1*003  : : *5  : x 

x—  2*008. 

This  quantity  will,  of  course,  require  more  nitric  acid  for  solution  than 
was  previously  used  (use  10  c.  c.).  In  cases  where  the  highest  degree  of 
accuracy  is  not  required,  the  results  afforded  by  this  rough  preliminary 
estimation  will  be  accurate  enough  if  the  experiment  is  carefully  conducted, 
since  they  give  the  quantity  of  silver  present  to  within  yoVo  or  wo* 

With  alloys  which  contain  sulphur,  and  with  such  as  consist  of  gold 
and  silver,  and  contain  a little  tin,  Levol  * employs  concentrated  sulphuric 
acid  (about  25  grm.)  as  solvent.  The  portion  of  the  alloy  is  boiled  with 
it  till  dissolved  ; after  cooling,  the  fluid  is  treated  in  the  usual  manner. 
As,  however,  concentrated  sulphuric  acid  fails  to  dissolve  all  the  silver 
when  there  is  much  copper  present,  Mascazzini  f digests  the  weighed 
portion  of  alloy  (which  may  contain  small  quantities  of  lead,  tin,  and 
antimony,  besides  gold)  first  with  the  least  possible  amount  of  nitric  acid, 


* Anna!,  de  China,  et  de  Phys.  3 s6r.  44,  347.  f Chem.  Centralbl.  1857,  300. 


OXIDE  OF  SILVER. 


215 


115.] 


as  long  as  red  vapors  are  formed  ; he  then  adds  concentrated  sulphuric 
acid,  boils  till  the  gold  has  settled  well  together,  adds  water  after  cooling, 
and  then  proceeds  to  the  assay. 


2.  Pisasti’s  Method.* 

This  process  depends  on  the  following  reaction  : a solution  of  iodide  of 
starch  added  to  a neutral  solution  of  nitrate  of  silver  forms  iodide  of  silver 
and  (in  all  probability)  iodate  of  silver.  The  blue  color  consequently 
vanishes,  and  on  continued  additions  of  the  iodide  of  starch,  the  fluid  does 
not  become  permanently  blue  till  all  the  nitrate  of  silver  present  is  decom- 
posed in  the  above  manner.  The  iodide  of  starch  solution  used  is  there- 
fore proportional  to  the  quantity  of  nitrate  of  silver.  Hence,  if  the  value 
of  the  iodide  of  starch  solution  be  determined,  by  allowing  it  to  act  on  a, 
certain  amount  of  silver  solution  of  known  strength,  we  shall  be  able  to 
estimate  unknown  quantities  of  silver  with  the  greatest  ease,  provided 
that  the  silver  solution  is  free  from  all  other  substances  which  exert 
a decomposing  action  on  the  iodide  of  starch.  Besides  the  ordinary 
reducing  agents,  the  following  salts  must  be  especially  mentioned  as 
possessing  this  power  : the  salts  of  suboxide  and  protoxide  of  mercury, 
of  protoxide  of  tin,  of  teroxide  of  antimony,  of  arsenious  acid,  of  pro- 
toxide of  iron  and  of  protoxide  of  manganese,  also  chloride  of  gold  ; salts 
of  lead  and  of  copper,  on  the  other  hand,  do  not  affect  iodide  of  starch. 

The  iodide  of  starch  is  prepared  as  follows  : make  an  intimate  mixture 
in  a mortar  of  2 grm.  iodine  and  15  grm.  starch  with  the  addition  of  6 
to  8 drops  of  water,  and  heat  the  slightly  moist  mixture  in  a closed  flask 
in  a water-bath,  till  the  original  violet-blue  color  has  passed  into  dark 
grayish-blue — it  takes  about  an  hour.  The  iodide  of  starch  thus  pre- 
pared is  then  digested  with  water ; it  dissolves  completely  to  a deep 
bluish-black  fluid. 

The  value  of  this  fluid  is  determined  by  allowing  it  to  act  on  10  c.  c. 
of  a neutral  solution  of  nitrate  of  silver,  containing  1 grm.  of  pure  silver 
in  1 litre, — the  silver  solution  is  mixed  with  a little  pure  precipitated 
carbonate  of  lime  before  adding  the  iodide  of  starch.  The  strength  of 
this  latter  is  right,  if  50  to  60  c.  c.  are  used  in  this  experiment.  On 
adding  it,  at  first  the  bjue  color  disappears  rapidly,  and  the  fluid  becomes 
yellowish  from  the  iodide  of  silver.  The  end  of  the  operation  is  attained 
as  soon  as  the  fluid  is  bluish-green.  The  point  is  pretty  easy  to  hit,  and 
an  error  of  0*5  c.  c.  is  of  no  importance,  as  it  only  corresponds  to  about 
0*0001  grm.  of  silver.  The  carbonate  of  lime,  besides  neutralizing  the 
free  acid,  has  the  effect  of  rendering  the  final  change  of  the  color  more 
distinctly  observable.  To  analyze  an  alloy  of  silver  and  copper,  dis- 
solve about  0*5  grm.  in  nitric  acid,  dilute  to  100  c.  c.  to  lower  the  color 
of  the  copper,  saturate  5 c.  c.  with  carbonate  of  lime,  and  add  iodide  of 
starch  till  the  coloration  appears.  Or,  you  may  determine  very  approxi- 
mately the  amount  of  silver  in  2 c.  c.  of  the  solution,  then  precipitate 
the  greater  part  (about  99^)  of  the  silver  from  50  c.  c.  of  the  solution 
with  standard  solution  of  chloride  of  sodium,  filter  (for  the  chloride  of 
silver  also  exercises  a decolorizing  action),  and  estimate  the  remainder 
of  the  silver  by  means  of  iodide  of  starch.  If  the  amount  of  silver  to  be 
determined  is  more  than  0*020  grm.,  it  is  always  better  to  employ  the 


* Annal.  d.  Min. , x.  83. 


216 


DETERMINATION. 


L§  He. 


latter  method.  In  the  case  of  a nitric  acid  solution  containing  silver 
with  lead,  the  latter  metal  is  first  precipitated  with  sulphuric  acid  and 
filtered  off,  carbonate  of  lime  is  added  to  the  filtrate  till  all  free  acid  is 
neutralized,  the  fluid  is  filtered  again  (if  necessary),  and  lastly,  more 
carbonate  of  lime  is  added,  and  then  the  iodide  of  starch.  Yery  dilute 
solutions  may  be  concentrated,  so  that  one  may  have  no  more  than 
from  50  to  100  c.  c.  to  deal  with.  The  method  is  specially  suited  for 
the  estimation  of  small  quantities  of  silver.  With  such  it  has  afforded 
me  perfectly  satisfactory  results. 

Instead  of  the  standard  iodide  of  starch,  a dilute  standard  solution 
of  iodine  in  iodide  of  potassium  may  be  equally  well  employed, — with 
addition  of  starch  solution  (Field  *). 


§116. 

2.  Oxide  of  Lead. 


a.  Solution. 

Few  of  the  salts  of  lead  are  soluble  in  water.  Metallic  lead,  oxide 
of  lead,  and  most  of  the  salts  of  lead  that  are  insoluble  in  water  dissolve 
in  dilute  nitric  acid.  Concentrated  nitric  acid  effects  neither  complete 
decomposition  nor  complete  solution,  since,  owing  to  the  insolubility  of 
nitrate  of  lead  in  concentrated  nitric  acid,  the  first  portions  of  nitrate 
formed  protect  the  yet  undecomposed  parts  of  the  salt  from  the  action 
of  the  acid.  For  the  solubility  of  chloride  and  sulphate  of  lead,  see 
§ 83.  As  we  shall  see  below,  the  analysis  of  these  compounds  may  be 
effected  without  dissolving  them.  Iodide  of  lead  dissolves  readily  in 
moderately  dilute  nitric  acid  upon  application  of  heat,  with  separation 
of  iodine.  Solution  of  potassa  is  the  only  menstruum  in  which  chro- 
mate of  lead  dissolves  without  decomposition ; for  the  purpose  of  analy- 
sis, the  chromate  is  best  converted  into  the  chloride  (see  below).  Sul- 
phide of  lead  may  be  converted  at  once  into  sulphate  (see  § 116,  2). 

b.  Determination. 

Lead  may  be  determined  as  oxide,  sulphate , chromate , or  sulphide  / 
also  by  volumetric  analysis. 

We  may  convert  into 


1.  Oxide  of  Lead. 

a.  By  Precipitation. 

All  salts  of  lead  soluble  in  water,  and  those  of  its  salts  which,  insolu- 
ble in  that  menstruum,  dissolve  in  nitric  acid,  with  separation  of  their 
acid. 

b.  By  Ignition. 

a.  Salts  of  lead  with  readily  volatile  or  decomposable  inorganic  acids. 
0.  Salts  of  lead  with  organic  acids. 


Chem.  News,  ii.  17. 


§ 116.] 


OXIDE  OF  LEAD. 


217 


2.  Sulphide  of  Lead. 

All  salts  of  lead  in  solution. 

3.  Sulphate  of  Lead. 

a.  By  Precipitation. 

The  salts  that  are  insoluble  in  water,  but  soluble  in  nitric  acid,  whose 
acid  cannot  be  separated  from  the  solution. 

b.  By  Evaporation . 

a.  All  the  oxides  of  lead,  and  also  the  salts  of  lead  with  volatile 
acids. 

f 3 . Many  of  the  organic  compounds  of  lead. 

4.  Chromate  of  Lead. 

The  compounds  of  lead  soluble  in  water  or  nitric  acid. 

The  application  of  these  several  methods  must  not  be  understood  to  be 
rigorously  confined  to  the  compounds  specially  enumerated  under  their 
respective  heads  ; thus,  for  instance,  all  the  compounds  enumerated  sub 
1,  may  likewise  be  determined  as  sulphate  of  lead  ; and,  as  above  men- 
tioned, all  soluble  compounds  of  lead  may  be  converted  into  sulphide  of 
lead ; also,  in  sulphate  of  lead  the  lead  may  be  without  difficulty  deter- 
mined as  sulphide.  Chloride,  bromide,  and  iodide  of  lead  are  most  con- 
veniently reduced  to  the  metallic  state  in  a current  of  hydrogen  gas,  in 
the  manner  described  § 115  (Reduction  of  chloride  of  silver),  if  it  is  not 
deemed  preferable  to  dissolve  them  in  water,  or  to  decompose  them  by 
a boiling  solution  of  carbonate  of  soda.  If  the  reduction  method  is 
resorted  to,  the  heat  applied  should  not  be  too  intense,  since  this  might 
cause  some  chloride  of  lead  to  volatilize. 

The  higher  oxides  of  lead  are  reduced  by  ignition  to  the  state  of  sim- 
ple oxide,  and  may  thus  be  readily  analyzed  and  dissolved.  Should  the 
operator  wish  to  avoid  having  recourse  to  ignition,  the  most  simple 
mode  of  dissolving  the  higher  oxides  of  lead  is  to  act  upon  them  with 
dilute  nitric  acid,  with  the  addition  of  alcohol.  For  the  methods  of 
analyzing  sulphate,  chromate,  iodide,  and  bromide  of  lead,  I refer  to  the 
paragraphs  treating  of  the  corresponding  acids,  in  the  second  part  of 
this  Section.  To  effect  the  estimation  of  lead  in  the  oxide  and  in  many 
salts  of  lead,  especially  also  in  the  sulphate,  the  compound  under  ex- 
amination may  be  fused  with  cyanide  of  potassium,  and  the  metallic 
lead  obtained  well  washed,  and  weighed.  From  the  sulphide  also  the 
greater  portion  of  the  lead  may  be  separated  by  this  method,  but  never 
the  whole  (H.  Rose  *). 

1.  j Determination  as  Oxide. 

a.  By  Precipitation. 

Mix  the  moderately  dilute  solution  with  carbonate  of  ammonia  f 


* Pogg.  Annal.  91,  144. 

f Oxalate  of  ammonia,  which  has  been  so  highly  recommended  as  a precipitant 
for  lead,  is  not  so  delicate  as  the  carbonate.  My  experience  in  this  respect  co- 
incides with  F.  Mohr’s  (Expt.  No.  48). 


218 


DETERMINATION. 


L§  H6. 

slightly  in  excess,  add  some  caustic  ammonia,  apply  a gentle  heat,  and, 
after  some  time,  filter.  Wash  the  precipitate  with  pure  water,  dry, 
and  ignite  in  a porcelain  crucible,  having  previously  incinerated  the 
filter  on  the  lid.  For  the  properties  of  the  precipitate  and  residue,  see 
§ 83.  The  results  are  satisfactory,  although  generally  a trifle  too  low, 
owing  to  carbonate  of  lead  not  being  absolutely  insoluble,  particularly 
in  fluids  rich  in  ammoniacal  salts  (Expt.  No.  47).  A small  and 
thin  filter  should  be  used,  and  care  taken  to  remove  the  precipitate 
as  completely  as  practicable  before  proceeding  to  incineration  ; other- 
wise additional  loss  of  substance  might  be  incurred,  from  reduction  of 
the  adhering  particles  of  the  carbonate  to  metallic  lead. 

b.  Ignition. 

Compounds  like  carbonate  or  nitrate  of  lead  are  cautiously  ignited 
in  a porcelain  crucible,  until  the  weight  remains  constant.  In  case  of 
salts  of  lead  with  organic  acids,  the  substance  is  very  gently  heated  in  a 
small  covered  porcelain  crucible,  which  is  included  within  a large  one, 
also  covered,  until  the  organic  matter  is  completely  carbonized  ; the  lids 
are  then  removed,  when  the  mass  begins  to  ignite,  and  a mixture  of 
oxide  of  lead  with  metallic  lead  results,  which  may  still  contain  uncon- 
sumed carbon.  A few  pieces  of  recently  fused  nitrate  of  ammonia  are 
now  thrown  into  the  inner  crucible,  which  has  previously  been  removed 
from  the  flame,  and  both  are  again  covered.  The  salt  fuses,  oxidizes  the 
lead,  and  converts  it  partly  into  nitrate.  The  whole  is  now  very  grad- 
ually raised  to  a red  heat,  until  no  more  fumes  of  hyponitric  acid  escape. 
The  residuary  oxide  is  then  weighed. 

The  results  are  satisfactory. 

2.  Determination  as  Sulphide. 

Lead  may  be  completely  precipitated  from  acid,  neutral,  and  alkaline 
solutions  by  sulphuretted  hydrogen,  and  also  from  neutral  and  alkaline 
solutions  by  sulphide  of  ammonium.  Precipitation  from  acid  solution 
is  usually  employed,  especially  in  separations.  A large  excess  of  acid 
and  also  warming  should  both  be  avoided.  The  former  is  prejudicial 
to  complete  precipitation  (§  83,  e),  the  latter  may  readily  occasion  the 
re-solution  of  the  sulphide  that  has  already  been  precipitated.  In  order 
to  guard  against  incomplete  precipitation,  before  filtering,  test  a portion 
of  the  supernatant  fluid  by  mixing  with  a relatively  large  quantity  of 
strong  sulphuretted  hydrogen  water ; of  course  the  mixture  should  re- 
main clear. 

After  the  sulphide  has  been  filtered  off,  washed  with  cold  water,  and 
dried,  it  is  transferred,  together  with  the  filter-ash,  to  a porcelain  cruci- 
ble, a little  sulphur  added,  and  ignited  in  hydrogen  till  its  weight  is 
constant.  It  should  always  be  allowed  to  cool  in  a current  of  the  gas, 
before  being  weighed.  As  regards  the  apparatus,  see  § 108,  2,  fig. 
47.  For  the  properties  of  the  residue,  see  § 83,  e.  The  results  are  very 
satisfactory  (H.  Pose).  The  heat  of  the  ignition  must  not  be  too  low, 
or  the  residue  will  contain  too  much  sulphur ; nor  too  high,  or  the  sul- 
phide of  lead  will  begin  to  volatilize.*  Drying  the  precipitate  at  100° 

[*  According  to  Souchay,  the  ignition  must  not  last  more  than  5-10  minutes, 
and  only  the  base  of  the  crucible  (to  one-fourth  its  height)  should  be  heated  to 
redness ; even  then  the  result  is  likely  to  fall  out  slightly  too  low.  Fres.  Zeitschrift, 
IV.  65.  J 


OXIDE  OF  LEAD. 


219 


§ 116-1 

cannot  be  recommended  (§  83,  e).  If,  for  want  of  a suitable  apparatus, 
the  ignition  in  hydrogen  cannot  be  performed,  the  dry  sulphide  may  be 
converted  into  sulphate  and  then  weighed.  To  this  end  it  is  trans- 
ferred to  a beaker,  the  filter-ash  added,  then  fuming  nitric  acid,  drop 
by  drop,  the  vessel  being  kept  covered  with  a glass  plate.  When  the 
oxidation  is  finished,  a gentle  heat  is  applied  for  some  time,  and  the 
contents  of  the  beaker  are  then  poured  into  a small  porcelain  dish,  the 
former  is  rinsed,  a few  drops  of  sulphuric  acid  are  added,  the  mixture  is 
carefully  evaporated,  and  the  residue  ignited.  The  accuracy  of  the 
result  is  entirely  dependent  on  the  care  with  which  the  operation 
is  conducted.  Fuming  nitric  must  be  used,  as  directed,  for  oxidizing 
the  precipitate,  otherwise  sulphur  separates,  which,  on  warming  with 
weaker  acid,  fuses,  and  only  oxidizes  with  extreme  slowness. 

3.  Determination  as  Sulphate. 

a.  By  Precipitation. 

a.  Mix  the  solution  (which  should  not  be  over-dilute)  with  moder- 
ately dilute  pure  sulphuric  acid  slightly  in  excess,  and  add  to  the  mix- 
ture double  its  volume  of  spirit  of  wine ; wait  a few  hours,  to  allow  the 
precipitate  to  subside ; filter,  wash  the  precipitates  with  spirit  of  wine, 
dry,  and  ignite,  after  the  method  described  in  § 53.  Though  a careful 
operator  may  use  a platinum  crucible,  still  a thin  porcelain  crucible 
is  preferable.  A small  and  thin  filter  should  be  employed,  and  the  ad- 
hering sulphate  of  lead  carefully  removed  before  proceeding  to  incinera- 
tion (see  l,  a). 

J3.  In  cases  where  the  addition  of  spirit  of  wine  is  inadmissible,  a 
greater  excess  of  sulphuric  acid  must  be  used,  and  the  precipitate, 
which  is  allowed  some  time  to  subside,  filtered,  and  washed  first  with 
water  acidulated  with  a few  drops  of  sulphuric  acid,  then  repeatedly 
with  spirit  of  wine.  The  remainder  of  the  process  is  conducted  as 
in  a. 

For  the  properties  of  the  precipitate,  see  § 83.  The  method  a gives 
accurate  results ; those  obtained  by  f3  are  less  exact  (a  little  too  low), 
but  still,  however,  satisfactory,  if  the  directions  given  are  adhered  to.  If, 
on  the  contrary,  a proper  excess  of  sulphuric  acid  is  not  added,  in  the 
presence,  for  instance,  of  ammoniacal  salts,  nitric  acid,  &c.,  the  lead  is 
not  completely  precipitated,  and  if  pure  water  is  used  for  washing,  de- 
cided traces  of  the  precipitate  are  dissolved. 

b.  By  Evaporation. 

a.  Put  the  substance  into  a weighed  dish,  dissolve  in  dilute  nitric 
acid,  add  moderately  dilute  pure  sulphuric  acid  slightly  in  excess,  and 
evaporate  at  a gentle  heat,  best  over  a heated  iron  cup,  until  the  excess 
of  sulphuric  acid  is  completely  expelled.  In  the  absence  of  organic  sub- 
stances, the  evaporation  may  be  effected  without  fear  in  a platinum 
dish ; but  if  organic  substances  are  present,  a light  porcelain  dish  is  pre- 
ferable. With  due  care  in  the  process  of  evaporation,  the  results  are 
perfectly  accurate. 

f 3 . Organic  compounds  of  lead  are  converted  into  the  sulphate  by  treat- 
ing them,  in  a porcelain  crucible,  with  pure  concentrated  sulphuric  acid  in 
excess,  evaporating  cautiously  in  the  well-covered  crucible  until  the 


220 


DETERMINATION-. 


[§  117. 


excess  of  sulphuric  acid  is  completely  expelled,  and  igniting  the  residue. 
Should  the  latter  not  look  perfectly  white,  it  must  be  moistened  once 
more  with  sulphuric  acid,  and  the  operation  repeated.  The  method  gives, 
when  conducted  with  great  care,  accurate  results ; a trifling  loss  is,  how- 
ever, usually  incurred,  the  escaping  sulphurous  acid  and  carbonic  acid 
gases  being  liable  to  carry  away  traces  of  the  salt. 

4.  Determination  as  Chromate  of  Lead. 

If  the  solution  is  not  already  distinctly  acid,  render  it  so  with  acetic 
acid,  then  add  bichromate  of  potassa  in  excess,  and,  if  free  nitric  acid  has 
been  present,  add  acetate  of  soda  in  sufficient  quantity  to  replace  the  free 
nitric  acid  by  free  acetic  acid  ; let  the  precipitate  subside  at  a gentle  heat, 
and  collect  on  a weighed  filter  dried  at  100°  ; wash  with  water,  dry  at 
100°,  and  weigh.  The  precipitate  may  also  be  ignited  according  to  § 53, 
but  in  this  case  care  must  be  taken  that  hardly  any  of  the  salt  remains 
adhering  to  the  paper,  and  that  the  heat  is  not  too  high.  Tor  the 
properties  of  the  precipitate,  see  8 93,  2.  The  results  are  accurate. 
(Expt.  No.  76.) 

5.  Determination  of  Lead  by  Volumetric  Analysis. 

H.  Schwarz’s  new  method.*  To  the  nitric  acid  solution  add  ammo- 
nia or  carbonate  of  soda,  as  long  as  the  precipitate  redissolves  on  shak- 
ing; mix  with  acetate  of  soda  in  not  too  small  quantity,  and  then  run  in 
from  a burette  a solution  of  bichromate  of  potash  (containing  14*759 
grm.  in  the  litre)  till  the  precipitate  begins  to  settle  rapidly.  Now  place 
on  a porcelain  plate  a number  of  drops  of  a solution  of  neutral  nitrate 
of  silver,  and  proceed  with  the  addition  of  the  chromate,  two  or  three 
drops  at  a time,  stirring  carefully  after  each  addition.  When  the  pre- 
cipitate has  settled  tolerably  clear,  which  takes  only  a few  -seconds,  re- 
move a drop  of  the  supernatant  liquid  and  mix  it  with  one  of  the  drops 
of  silver  on  the  plate.  A small  excess  of  chromate  gives  at  once  a dis- 
tinct red  coloration ; the  precipitated  chromate  of  lead  does  not  act  on 
the  silver  solution,  but  remains  suspended  in  the  drop.  The  number  of 
c.  c.  of  solution  of  chromate  used  ( minus  0*1,  which  Schwarz  deducts 
for  the  excess)  multiplied  by  0*0207 =the  quantity  of  lead.  If  the  fluid 
appear  yellow  before  the  reaction  with  the  silver  salt  occurs,  acetate  of 
soda  is  wanting.  In  such  a case,  first  add  more  acetate  of  soda,  then  1 
c.  c.  of  a solution  containing  0*0207  lead  in  1 c.  c.,  complete  the  process 
in  the  usual  way,  and  deduct  1 c.  c.  from  the  quantity  of  chromate  used 
on  account  of  the  extra  lead  added.  Any  iron  present  must  be  in  the 
form  of  sesquioxide ; metals  whose  chromates  are  insoluble,  must  be 
removed  before  the  method  can  be  employed. 


§ 117. 

3.  Suboxide  of  Mercury. 

a.  Solution. 

Suboxide  of  mercury  and  its  compounds  may  generally  be  dissolved 
by  means  of  dilute  nitric  acid,  but  without  application  of  heat  if  conver- 
sion of  any  of  the  suboxide  into  oxide  is  to  be  avoided.  If  all  that  is 
required  is  to  dissolve  the  mercury,  the  easiest  way  is  to  warm  the  sub- 
stance for  some  time  with  nitric  acid,  then  add  hydrochloric  acid,  drop 


* Dingl.  Polyt.  Joum.  169,  284. 


SUBOXIDE  OF  MERCURY. 


221 


§ 117.] 

by  drop,  and  continue  the  application  of  a moderate  heat  until  a perfectly 
clear  solution  is  produced,  which  now  contains  all  the  mercury  as  oxide 
and  chloride.  Heating  the  solution  to  boiling  must  be  carefully  avoided, 
as  otherwise  chloride  of  mercury  may  escape  with  the  steam. 

b.  Determination. 

If  it  is  impracticable  to  produce  a solution  of  the  suboxide  or  its  com- 
pounds perfectly  free  from  oxide,  and  it  becomes  accordingly  necessary 
to  convert  the  mercury  completely  into  oxide,  the  latter  is  determined 
as  directed  § 118.  But  if  a solution  of  suboxide  has  been  obtained, 
quite  free  from  oxide,  the  determination  of  the  suboxide  may  be  based 
upon  the  insolubility  of  subchloride  of  mercury,  and  effected  either 
gravimetrically  or  volumetrically.  The  process  of  determining  mercury, 
described  § 118,  1,  a,  may,  of  course,  be  applied  equally  well  in  the  case 
of  compounds  of  suboxide  of  mercury. 

1.  Determination  as  Subchloride  of  Mercury. 

Mix  the  cold  highly  dilute  solution  with  solution  of  chloride  of  sodium, 
as  long  as  a precipitate  forms ; let  the  precipitate  subside,  collect  on  a 
weighed  filter,  dry  at  100°,  and  weigh.  For  the  properties  of  the  pre- 
cipitate, see  § 84.  Results  accurate. 

If  the  solution  of  suboxide  of  mercury  contains  much  free  nitric  acid, 
the  greater  part  of  this  should  be  neutralized  with  carbonate  of  soda 
before  adding  the  chloride  of  sodium. 

2.  Volumetric  Methods. 

Several  methods  have  been  proposed  under  this  head : the  following 
are  those  which  are  most  worthy  of  recommendation  : — 

a.  Mix  the  cold  solution  with  decinormal  solution  of  chloride  of  sodium 
(§  117,  #),  until  this  no  longer  produces  a precipitate,  and  is  accord- 
ingly present  in  excess  ; filter  and  wash  thoroughly,  taking  care,  however, 
to  limit  the  quantity  of  water  used  ; add  a few  drops  of  solution  of  chro- 
mate of  potassa,  then  pure  carbonate  of  soda,  sufficient  to  impart  a light 
yellow  tint  to  the  fluid,  and  determine,  by  means  of  solution  of  nitrate 
of  silver  (§  141,  b,  a),  the  quantity  of  chloride  of  sodium  in  solution, 
consequently  the  quantity  which  has  been  added  in  excess ; this  shows, 
of  course,  also  the  amount  of  chloride  of  sodium  consumed  in  effecting 
the  precipitation.  One  equivalent  of  Hg2  O is  reckoned  for  every  equi- 
valent of  Na  Cl,  consequently  for  every  c.  c.  of  the  decinormal  solution 
of  chloride  of  sodium,  0*0208  grm.  of  suboxide  of  mercury.  As  filtering 
and  washing  form  indispensable  parts  of  the  process,  this  method  affords 
no  great  advantage  over  the  gravimetric ; however,  the  results  are  accu- 
rate (Fr.  Mohr  *).  The  two  methods,  1 and  2,  a , may  also  be  advan- 
tageously combined. 

b.  The  solution  containing  the  mercury  in  the  form  of  suboxide  is 
diluted  with  enough  water,  gently  warmed,  and  solution  of  hyposulphite 
of  soda — 12*4  grms.  in  the  litre — added  (waiting  a little  and  shaking 
vigorously  after  each  addition),  till  the  last  drop  gives  no  brown  colora- 
tion. The  subsulphide  of  mercury  formed  subsides  well  and  quickly, 
and  the  end  of  the  reaction  is  easy  to  perceive  (Hg20,  N 05-|-Na  O,  S2 
02=Hg2  S-f-Ha  O,  S Og-j-N  06).  Each  1 c.  c.  of  the  solution  employed 
= *0208  suboxide  of  mercury  or  *0200  mercury.  Results  accurate  (J.  J. 
Scherer  f). 


* Lehrbuch  der  Titrirmethode,  ii.  62.  f His  Lehrbuch  der  Chemie,  1,  511. 


222 


DETERMINATION-. 


L§  ns. 


§118. 

4.  Oxide  of  Mercury. 

a.  Solution. 

Oxide  of  mercury,  and  those  of  its  compounds  which  are  insoluble  in 
water,  are  dissolved,  according  to  circumstances,  in  hydrochloric  acid  or 
in  nitric  acid.  Sulphide  of  mercury  is  heated  with  hydrochloric  acid, 
and  nitric  acid  or  chlorate  of  potassa  added  until  complete  solution  en- 
sues ; it  is,  however,  most  readily  dissolved  by  suspending  it  in  dilute 
potassa  and  transmitting  chlorine,  at  the  same  -time  gently  warming  (H. 
Rose).  When  a solution  of  chloride  of  mercury  is  evaporated  on  the 
water-bath,  chloride  of  mercury  escapes  with  the  aqueous  vapor. 

b.  Determination. 

Mercury  may  be  weighed  in  the  metallic  state , or  as  subchloride,  sul- 
phide, or  oxide  (84)  ; in  separations  it  is  sometimes  determined  as  loss  on 
ignition.  It  may  also  be  estimated  volumetrically. 

The  three  first  methods  may  be  used  in  almost  all  cases ; the  determi- 
nation as  oxide,  on  the  contrary,  is  possible  only  in  compounds  of  the 
oxide  or  suboxide  with  nitric  acid.  The  methods  by  which  the  mercury 
is  determined  as  subchloride  or  sulphide  are  to  be  preferred  before  those 
in  which  it  is  separated  in  the  metallic  form.  Of  the  volumetric  methods 
the  first  can  be  employed  in  many  cases,  while  the  second  and  third  are 
only  of  very  limited  application. 

1.  Determination  as  Metallic  Mercury, 
a.  In  the  Dry  Way. 

The  process  is  conducted  in  the  apparatus  illustrated  by  fig.  50. 


Fig.  50. 

Take  a tube  eighteen  inches  long,  and  about  four  lines  wide,  made  of 
difficultly  fusible  glass,  and  sealed  at  one  end.  First  put  into  the  tube  a 
mixture  of  bicarbonate  of  soda  and  powdered  chalk,  then  a layer  of 
quick-lime ; these  two  will  occupy  the  space  from  a to  b.  (Let  the  mix- 
ture for  generating  carbonic  acid  take  up  about  two  inches).  Then  add 
the  intimate  mixture  of  the  substance  with  an  excess  of  quick-lime  ( b-c ), 
then  the  lime-rinsings  of  the  mortar  ( c-d ),  then  a layer  of  quick-lime 
( d~e ),  and  lastly,  a loose  stopper  of  asbestus  (?-/)•  The  anterior  end  of 
the  tube  is  then  drawn  out,  and  bent  at  a somewhat  obtuse  angle.  The 
manipulations  in  the  processes  of  mixing  and  filling  being  the  same  as 
in  organic  analysis,  they  will  be  found  in  detail  in  the  chapter  on  that 
subject. 

A few  gentle  taps  upon  the  table  are  sufficient  to  shake  the  contents 


OXIDE  OF  MERCURY. 


223 


§ ns-] 

of  the  tube  down  so  as  to  leave  a free  passage  through  the  whole  length 
of  the  tube.  The  tube,  so  prepared  and  arranged,  is  now  placed  in  a 
combustion  furnace,  the  point  being  inserted  into  a flask  containing 
water,  the  surface  of  which  it  should  just  touch,  so  that  the  opening  may- 
be just  closed. 

The  tube  is  now  surrounded  with  red-hot  charcoal,  in  the  same  way 
as  in  organic  analysis,  proceeding  slowly  from  e to  a,  the  last  traces  of 
mercurial  vapor  being  expelled  by  heating  the  mixture  at  the  sealed 
end  of  the  tube.  Whilst  the  tube  still  remains  in  a state  of  intense 
ignition,  the  neck  is  cut  off  at  /*,  and  carefully  and  completely  rinsed  in- 
to the  receiving,  flask,  by  means  of  a washing-bottle.  The  small  globules 
of  mercury  which  have  distilled  over  are  united  into  a large  one,  by  agi- 
tating the  flask,  and,  after  the  lapse  of  some  time,  the  perfectly  clear 
water  is  decanted,  and  the  mercury  poured  into  a weighed  porcelain 
crucible,  where  the  greater  portion  of  the  water  still  adhering  to  it  is 
removed  with  blotting-paper.  The  mercury  is  then  finally  dried  under 
a bell-jar,  over  concentrated  sulphuric  acid,  until  the  weight  remains 
constant.  Heat  must  not  be  applied.  For  the  properties  of  the  metal, 
see  § 84.  In  the  case  of  sulphides,  in  order  to  avoid  the  presence  of 
vapor  water  in  the  tube,  which  would  give  rise,  to  the  formation  of  sul- 
phuretted hydrogen,  the  mixture  of  bicarbonate  of  soda  and  chalk 
is  replaced  by  magnesite.  Iodide  of  mercury  cannot  be  completely 
decomposed  by  lime.  To  analyze  this  in  the  dry  way,  substitute  finely 
divided  metallic  copper  for  the  lime  (H.  Hose  *).  The  accuracy  of  the 
results  is  entirely  dependent  upon  the  care  bestowed.  The  most  highly 
accurate  results  are,  however,  obtained  by  the  application  of  the  some- 
what more  complicated  modification  adopted  by  Erdmann  and  Marchand 
for  the  determination  of  the  atomic  weight  of  mercury  and  of  sulphur.  For 
the  details  of  this  modified  process,  I refer  to  the  original  essay, f simply 
remarking  here,  that  the  distillation  is  conducted,  in  a combustion-tube, 
in  a current 'of  carbonic  gas,  and  that  the  distillate  is  received  in  a 
weighed  bulb  apparatus  with  the  outer  end  filled  with  gold-leaf,  to  in- 
sure the  condensation  of  every  trace  of  mercury  vapor.  This  way  of 
receiving  and  condensing  may  be  employed  also  in  the  analysis  of 
amalgams  (Konig  J). 

b.  In  the  Wet  Way. 

The  solution,  free  from  nitric  acid,  and  mixed  with  free  hydrochloric 
acid,  is  precipitated,  in  a flask,  with  an  excess  of  a clear  solution  of  proto- 
chloride of  tin,  containing  free  hydrochloric  acid;  the  mixture  is  boiled 
for  a short  time,  and  then  allowed  to  cool.  After  some  time,  the  perfectly 
clear  supernatant  fluid  is  decanted  from  the  metallic  mercury,  which,  under 
favorable  circumstances,  will  be  found  united  into  one  globule  ; if  this  is 
the  case,  the  globule  of  mercury  may  be  washed  at  once  by  decantation, 
first  with  water  acidulated  with  hydrochloric  acid,  and  finally  with  pure 
water ; it  is  dried  as  in  a. 

If,  on  the  other  hand,  the  particles  of  the  mercury  have  not  united, 
their  union  in  one  globule  may  as  a rule  be  readily  effected  by  boiling  a 
short  time  with  some  moderately  dilute  hydrochloric  acid  mixed  with  a 


* Fogg.  Anna!  110,  546. 

f Journ.  f.  prakt  Chem.  31,  385  ; also  Pharm.  Centralbl.  1844,  354. 
X Joum.  f.  prakt.  Chem.  70,  64. 


22  4 


DETERMINATION. 


[§  H8. 

few  drops  of  protochloride  of  tin  (having,  of  course,  previously  removed  by 
decantation  the  supernatant  clear  fluid).  For  the  properties  of  metallic 
mercury,  see  § 84. 

Instead  of  protochloride  of  tin,  other  reducing  agents  may  be  used, 
especially  phosphorous  acid  at  a boiling  temperature.  This  method 
gives  accurate  results  only  when  conducted  with  the  greatest  care.  In 
general,  a little  mercury  is  lost  (Comp.  Expt.  No.  77). 

2.  Determination  as  Subchloride  of  Mercury. 

a.  After  H.  Rose.*  Mix  the  solution  of  mercury,  which  may  contain 
nitric  acid,  with  hydrochloric  acid  and  excess  of  phosphorous  acid  (obtained 
by  the  deliquescence  of  phosphorus  in  moist  air),  allow  to  stand  for  12 
hours  in  the  cold  or  at  a very  gentle  heat  (at  all  events  under  60°),  collect 
the  mercury,  now  completely  separated  as  subchloride,  on  a weighed  filter, 
wash  with  hot  water,  dry  at  100°,  and  weigh.  Results  perfectly  satis- 
factory. 

b.  Mix  the  moderately  dilute  solution  of  oxide  of  mercury,  which  may 
contain  nitric  acid,  with  a sufficient  quantity  of  chloride  of  sodium  (if 
enough  hydrochloric  acid  is  not  already  present),  add  a solution  of  proto- 
sulphate of  iron  (for  1 grm.  Hg  O at  least  3 grm.  of  the  iron  salt),  then 
solution  of  soda  in  excess,  whereby  a brownish-black  precipitate  falls, 
which  is  a mixture  of  suboxide  of  mercury  and  protosesquioxide  of 
iron  (2  Hg  O -fi  3 Fe  O = Hg2  O + Fe3  04).  Digest  with  shaking  for 
a few  minutes,  add  dilute  sulphuric  acid  in  excess  and  allow  to  stand, 
shaking  every  now  and  then,  till  the  dark-colored  precipitate  has  turned 
pure  white,  i.e.  till  the  suboxide  of  mercury  is  completely  converted  into 
subchloride  by  the  free  hydrochloric  acid.  Collect  on  a weighed  filter, 
wash,  dry  at  100°,  and  weigh.  Results  accurate  (Hempel  j). 

3.  Determination  as  Sulphide  of  Mercury. 

The  solution  is  sufficiently  diluted,  acidulated  with  hydrochloric  acid, 
and  precipitated  with  clear  saturated  sulphuretted  hydrogen  water  (or  in 
the  case  of  large  quantities,  by  passing  the  gas)  ; filter  after  allowing  the 
precipitate  a short  time  to  deposit,  wash  quickly  with  cold  water,  dry  at 
100°,  and  weigh.  Results  very  satisfactory. 

If  from  any  cause  ( e.g . presence  of  sesquioxide  of  iron,  free  chlorine,  or 
the  like)  the  precipitate  should  contain  free  sulphur,  the  filter  is  spread 
out  on  a glass  plate,  the  precipitate  removed  to  a porcelain  dish  by  the  aid 
of  a jet  from  the  wash-bottle,  and  warmed  for  some  time  with  a moderately 
strong  solution  of  sulphite  of  soda.  The  filter,  having  been  in  the  mean 
while  somewhat  dried  on  the  glass  plate,  is  replaced  in  the  funnel,  the 
supernatant  fluid  is  poured  on  to  it,  the  treatment  with  sulphite  of  soda  is 
repeated,  and  the  precipitate  (now  free  from  sulphur)  is  finally  collected 
on  the  filter,  washed,  dried,  and  weighed.  Results  very  good  (J.  Lowe  J). 

Should  the  quantity  of  sulphur  mixed  with  the  precipitate  be  not  very 
large,  it  may  be  removed  also  as  follows  : the  precipitate  is  first  washed 
with  water,  then  twice  with  strong  alcohol,  then  repeatedly  with  bisul- 
phide of  carbon,  till  a few  drops  of  the  washings  evaporate  on  a watch* 


* Fogg1.  Annal.  110,  529. 

+ Annal.  d.  Chem.  u.  Pharm.  107,  97  ; and  110,  177. 
; Journ.  f.  prakt.  Chem.  77,  73. 


OXIDE  OF  COPPER. 


225 


§ HO.] 


glass  without  leaving  a residue.  (The  precipitate  is  retained  on  the  filter 
throughout  this  operation.) 

Properties  of  the  sulphide  of  mercury,  § 84. 

4.  Determination  as  Oxide. 

In  the  salts  of  the  oxides  of  mercury,  with  nitrogen  acids,  the  metal 
may  be  very  conveniently  determined  in  the  form  of  oxide  (Marignac  *). 
For  this  purpose,  the  salt  is  heated  in  a bulb-tube,  of  which  the  one  end, 
drawn  out  to  a point,  dips  under  water,  the  other  end  being  connected 
with  a gasometer,  by  means  of  which  dry  air  is  transmitted  through  the 
tube,  as  long  as  the  application  of  heat  is  continued.  In  this  way  com- 
plete decomposition  of  the  salt  is  readily  effected,  without  reaching  the 
temperature  at  which  the  oxide  itself  would  be  decomposed. 

5.  Volumetric  Methods. 

After  J.  J.  Scherer. f The  nitrate  or  chloride  of  mercury  may  be 
directly  determined  with  hyposulphite  of  soda.  The  reactions  are  as 
follows : 3 (Hg  O,  N 06)  + 2 (Na  O, Sa  02 ) = (2  Hg  S + Hg  O,  N 05)  +2 
(Na O,  S 03)  + 2 N 05  and  3 Hg  Cl  + 2 (Na0,S202)  + 2HO=(2Hg 
S,  Hg  Cl)  -j-  2 (Na  O,  S03)  + 2 H Cl.  The  process  is  conducted  as  follows 
in  the  case  of  nitrate  of  mercury  : Mix  the  highly  dilute  solution  with  a 
little  free  nitric  acid  in  a tall  glass  and  add  drop  by  drop  solution  of  hypo- 
sulphite of  soda — 12’4  grm.  in  a litre.  Each  drop  produces  an  intense 
yellow  cloud,  which  on  shaking  quickly  subsides  in  the  form  of  a heavy 
flocculent  precipitate  (2  Hg  S 4-  Hg  O,  N 05).  In  order  to  distinguish 
clearly  the  exact  end  of  the  reaction,  Scherer  recommends  to  transfer 
the  fluid  towards  the  end  to  a measuring  flask,  to  take  out  or  4 of  the 
clear  fluid  and  to  finish  with  this.  The  portion  of  hyposulphite  last  used 
is  multiplied  by  3 or  2,  as  the  case  may  be,  and  added  to  the  quantity 
first  used.  1 c.  c.  of  the  solution  corresponds  to  *015  mercury,  or  *0162 
oxide  of  mercury.  The  relation  is  not  changed  even  when  the  fluid  con- 
tains another  acid  (sulphuric,  phosphoric). 

In  the  case  of  chloride  of  mercury,  the  highly  dilute  solution  is  mixed 
with  a little  hydrochloric  acid  and  warmed,  nearly  to  boiling,  before 
beginning  to  add  the  hyposulphite  of  soda.  At  first  a white  turbidity  is 
formed,  then  the  precipitate  separates  in  thick  flocks.  When  the  solution 
begins  to  appear  transparent,  the  precipitant  is  added  more  slowly.  In 
order  to  hit  the  end  of  the  reaction  exactly,  small  portions  must  be  filtered 
off  towards  the  close.  The  precipitate  must  be  completely  white  ; if  too 
much  hyposulphite  has  been  added,  it  is  gray  or  blackish,  and  the  experi- 
ment must  be  repeated.  Scherer  obtained  very  accurate  results.  Of 
course  no  other  metals  must  be  present  that  exert  a decomposing  action 
on  hyposulphite  of  soda. 


§119. 

5.  Oxide  of  Copper. 

a.  Solution. 

Metallic  copper  is  best  dissolved  in  nitric  acid.  Oxide  of  copper,  and 
those  of  its  salts  which  are  insoluble  in  water,  may  be  dissolved  in  nitric, 
hydrochloric,  or  sulphuric  acid.  Sulphide  of  copper  is  treated  with 

* Jahresber.  von  Liebig  u.  Kopp,  1849,  594. 

\ His  Lehrbuch  der  Chemie,  i.  513. 

15 


226 


DETERMINATION-. 


fuming  nitric  acid,  or  it  is  heated  with  moderately  dilute  nitric  acid, 
until  the  separated  sulphur  exhibits  a pure  yellow  tint ; addition  of  a 
little  hydrochloric  acid  or  chlorate  of  potassa  greatly  promotes  the  action 
of  the  dilute  acid.  [Native  sulphides  are  easily  decomposed  by  a mix- 
ture of  strong  nitric  and  sulphuric  acids.] 

b.  Determination. 

Copper  may  be  weighed  in  the  form  of  oxide , or  in  the  metallic  state , 
or  as  subsulphide  (§  85).  Into  the  form  of  oxide  it  is  converted  by  pre- 
cipitation or  ignition,  sometimes  with  previous  precipitation  as  sulphide. 
The  determination  as  subsulphide  is  preceded  usually  by  precipitation 
either  as  sulphide  or  as  sulphocyanide.  Copper  may  be  determined  also 
by  various  volumetric  and  indirect  methods. 

We  may  convert  into 

1.  Oxide  of  Copper. 

a.  By  direct  Precipitation  as  Oxide. 

All  salts  of  oxide  of  copper  soluble  in  water,  and  also  those  of  the  in- 
soluble salts,  the  acids  of  which  may  be  removed  upon  solution  in  nitric 
acid,  provided  no  non-volatile  organic  substances  be  present. 

b.  By  Precipitation , preceded  by  Ignition  of  the  Compound. 

Such  of  the  salts  enumerated  sub  a as  contain  a non-volatile  organic 

substance,  thus  more  particularly  salts  of  copper  with  non-volatile  organic 
acids. 

c.  By  Precipitation  as  Sulphide  of  Copper. 

All  compounds  of  copper  without  exception. 

d.  By  Ignition. 

Salts  of  copper  with  oxygen  acids  that  are  readily  volatile  or  decom- 
posable at  a high  temperature  (carbonate  of  copper,  nitrate  of  copper). 

2.  Metallic  Copper. 

Oxide  of  copper  in  all  solutions  free  from  other  metals  precipitable  by 
zinc. 

3.  Subsulphide  of  Copper. 

Oxide  of  copper  in  all  cases  in  which  no  other  metals  are  present  that 
are  precipitable  by  sulphuretted  hydrogen,  hyposulphite  of  soda,  or  sul- 
phocyanide of  potassium. 

Of  the  methods  of  estimating  copper,  I prefer — in  all  cases  where  the 
choice  is  left  free  and  where  precipitation  cannot  be  avoided — method 
2,  as  the  process  is  more  rapidly  performed  than  is  the  case  with  method 
1,  while  the  results  are,  at  least,  equally  accurate.  Method  3 finds  ap- 
plication chiefly  in  separations  of  copper  from  other  metals,  and  is,  as 
now  carried  out,  very  exact  and  convenient.  The  volumetric  methods 
are  especially  adapted  for  technical  purposes,  but  they  are  inferior  to 
method  2 in  simplicity  and  accuracy. 

1.  Determination  as  Oxide  of  Copper. 

a.  By  direct  Precipitation  as  Oxide. 

a.  From  Neutral  or  Acid  Solutions. 

Heat  the  rather  dilute  solution  in  a platinum  or  porcelain  dish,  to  in- 


OXIDE  OF  COPPER. 


227 


§ 119.] 

cipient  ebullition,  add  a somewhat  dilute  solution  of  pure  soda  or  potassa 
until  the  formation  of  a precipitate  ceases,  and  keep  the  mixture  a few 
minutes  longer  at  a temperature  near  boiling.  Allow  to  subside,  filter 
off  the  fluid,  wash  the  precipitate  by  decantation  twice  or  thrice,  boiling 
up  each  time,  then  collect  it  on  the  filter,  wash  thoroughly  with  hot 
water,  dry,  and  ignite  in  a platinum  crucible,  as  directed  § 53.  After 
intense  ignition,  and  having  added  the  ash  of  the  filter,  let  the  crucible 
cool  in  the  desiccator,  and  weigh.  The  action  of  reducing  gases  must  be 
carefully  guarded  against  in  the  process  of  ignition. 

It  will  sometimes  happen,  though  mostly  from  want  of  proper  atten- 
tion to  the  directions  here  given,  that  particles  of  the  oxide  of  copper 
adhere  so  tenaciously  to  the  dish  as  to  be  mechanically  irremovable.  In 
a case  of  this  kind,  after  washing  the  dish  thoroughly,  dissolve  the  ad- 
hering particles  with  a few  drops  of  nitric  acid,  and  evaporate  the  solu- 
tion over  the  principal  mass  of  the  precipitated  oxide,  before  you  proceed 
to  ignite  the  latter.  Should  the  solution  be  rather  copious,  it  must  first 
be  concentrated  by  evaporation,  until  only  very  little  of  it  is  left.  For 
the  properties  of  the  precipitate,  see  § 85. 

With  proper  attention  to  the  directions  here  given,  the  results  obtained 
by  this  method  are  quite  accurate,  otherwise  they  may  be  either  too  high 
or  too  low.  Thus,  if  the  solution  be  not  sufficiently  dilute,  the  precipi- 
tant will  fail  to  throw  down  the  whole  of  the  oxide  of  copper ; or,  if  the 
precipitate  be  not  thoroughly  washed  with  hot  water,  it  will  retain  a por- 
tion of  the  alkali ; or,  if  the  ignited  precipitate  be  allowed  to  stand  ex- 
posed to  the  air,  before  it  is  weighed,  an  increase  of  weight  will  be  the 
result ; and  so,  on  the  other  hand,  a diminution  of  weight,  if  the  oxide 
be  ignited  with  the  filter  or  under  the  influence  of  reducing  gases,  as 
thereby  suboxide  would  be  formed.  Should  a portion  of  the  oxide  have 
suffered  reduction,  it  must  be  reoxidized  by  moistening  with  nitric  acid, 
evaporating  cautiously  to  dryness,  and  exposing  the  residue  to  a gentle 
heat,  increasing  this  gradually  to  a high  degree  of  intensity. 

Let  it  be  an  invariable  rule  to  test  the  filtrate  for  copper  with  sulphu- 
retted hydrogen  water.  If,  notwithstanding  the  strictest  compliance 
with  the  directions  here  given,  the  addition  of  this  reagent  produces  a 
precipitate,  or  imparts  a brown  tint  to  the  fluid,  this  is  to  be  attributed 
to  the  presence  of  organic  matter;  in  that  case,  concentrate  the  filtrate 
and  wash-water  by  evaporation,  acidify,  precipitate  with  sulphuretted 
hydrogen  water,  treat  the  precipitated  sulphide  as  directed  in  c,  and  add 
the  oxide  obtained  to  the  first  precipitate  in  the  filter.  It  is  also  highly 
advisable  not  to  neglect  dissolving  the  oxide  of  copper,  after  weighing, 
in  hydrochloric  acid,  in  order  to  detect,  and,  if  necessary,  estimate,  any 
silicic  acid  which  might  be  present. 

j3.  From  Alkaline  Solutions. 

From  ammoniacal  solutions  also,  oxide  of  copper  may  be  precipitated 
by  soda  or  potassa.  In  the  main,  the  process  is  conducted  as  in  a.  A fter 
precipitation  the  mixture  is  heated,  until  the  supernatant  fluid  has  be- 
come perfectly  colorless ; the  fluid  is  then  filtered  off  with  the  greatest 
possible  expedition.  If  allowed  to  cool  with  the  precipitate  in  it  a small 
portion  of  the  latter  would  redissolve. 

b.  By  Precipitation  as  Oxide , preceded  by  Ignition  of  the  Substance . 

Heat  the  substance  in  a porcelain  crucible,  until  the  organic  matter 


228 


DETERMINATION. 


present  is  totally  destroyed ; dissolve  the  residue  in  dilute  nitric  acid, 
filter,  if  necessary,  and  treat  the  clear  solution  as  directed  in  a,  a. 

c.  JBy  Precipitation  as  Sulphide  of  Copper. 

Precipitate  the  solution — which  is  best  neutral,  or  slightly  acid,  hut 
should  not  contain  a great  excess  of  nitric  acid — according  to  the  quan- 
tity of  copper  present,  either  by  the  addition  of  strong  sulphuretted  hy- 
drogen water,  or  by  passing  the  gas.  When  the  precipitate  has  fully 
subsided,  and  you  have  made  sure  that  the  supernatant  fluid  is  no  longer 
colored  or  precipitated  by  strong  sulphuretted  hydrogen  water,  filter  off 
quickly,  wash  the  precipitate  without  intermission  with  water  contain- 
ing sulphuretted  hydrogen  (to  prevent  oxidation),*  and  dry  on  the  filter 
with-  some  expedition  ; transfer  the  dried  precipitate  to  a beaker,  incine- 
rate the  filter  in  a small  porcelain  dish,  add  the  ash  to  the  precipitate, 
treat  with  moderately  dilute  nitric  acid,  add  some  hydrochloric  acid,  and 
heat  gently  until  the  separated  sulphur  appears  of  a pure  yellow  color ; 
dilute  now  with  water,  filter,  and  precipitate  as  directed  in  a. 

Instead  of  precipitating  the  copper,  as  sulphide,  with  hydrosul- 
phuric  acid,  or  an  alkaline  sulphide,  it  may  also  be  precipitated  with 
hyposulphite  of  soda.  To  this  end,  the  solution  of  copper  (which,  if  ne- 
cessary, must  be  freed  as  far  as  practicable  from  hydrochloric  acid  and 
nitric  acid,  by  evaporation  with  sulphuric  acid)  is  sufficiently  diluted, 
heated  to  boiling,  and  mixed  with  a solution  of  hyposulphite  of  soda,  as 
long  as  a black  precipitate  forms.  As  soon  as  this  has  subsided,  leaving 
only  suspended  Sulphur  in  the  supernatant  fluid,  the  precipitation  of 
the  copper  is  complete.  The  precipitate  is  subsulphide  of  copper  (Cu.2 
S)  ; it  may  easily  be  washed  without  risk  of  oxidation  (Flajolot|). 
It  is  finally  converted  into  oxide  as  directed  in  1,  a. 

Instead  of  converting  the  sulphide  or  subsulphide  of  copper  into  ox- 
ide, I always  prefer  to  weigh  them  as  subsulphide,  see  3. 

d.  Py  Ignition . 

The  salt  is  put  into  a platinum  or  porcelain  crucible,  and  exposed  to 
a very  gentle  heat,  which  is  gradually  increased  to  intense  redness  ; the 
residue  is  then  weighed. 

As  nitrate  of  copper  spirts  strongly  when  ignited,  it  is  always  advisa- 
ble to  put  it  into  a small  covered  platinum  crucible,  and  to  place  the 
latter  in  a large  one,  also  covered.  With  proper  care,  the  results  are 
accurate.  Copper  salts  with  organic  acids  may  also  be  converted  into 
oxide  by  simple  ignition.  To  this  end,  the  residue  first  obtained,  which 
contains  suboxide,  is  completely  oxidized,  by  repeated  moistening  with 
nitric  acid,  and  ignition.  However,  a loss  of  substance  is  generally  in- 
curred in  this  process,  from  the  difficulty  of  avoiding  spirting. 

2.  Determination  as  Metallic  Copper\ 

a.  By  Precipitation  with  Zinc. 

Introduce  the  solution  of  copper,  after  having,  if  required,  first  freed 

[*  Mohr  finds  that  sulphide  of  copper,  when  precipitated  at  a boiling1  heat  by 
HS  from  solution  of  the  sulphate,  does  not  oxidize  by  exposure  to  the  air,  and 
washes  easily.] 

f Joum.  f.  prakt.  Chem.  61,  105. 

\ The  method  of  precipitating-  copper  by  iron  or  zinc,  and  weighing*  it  in  the 
metallic  form,  was  proposed  long  ago  ; see  Pfaff’s  Handbuch  der  analytischen 
Chemie,  Altona,  1822,  Bd.  2,  Seite  269,  where  the  reasons  are  given  for  prefer- 


§ 119.] 


OXIDE  OF  COPPER. 


229 


it  from  nitric  acid,  by  evaporation  with  hydrochloric  acid  or  sulphuric 
acid,  into  a weighed  platinum  dish ; dilute,  if  necessary,  with  some 
water,  throw  in  a piece  of  zinc,  soluble  in  hydrochloric  acid  without 
residue,  and  add,  if  necessary,  hydrochloric  acid  in  sufficient  quantity  to 
produce  a moderate  evolution  of  hydrogen.  If,  on  the  other  hand,  this 
evolution  should  be  too  brisk,  owing  to  too  large  excess  of  acid,  add  a 
little  water.  Cover  the  dish  with  a watch-glass,  which  is  afterwards 
rinsed  into  the  dish  with  the  aid  of  a washing-bottle.  The  separation 
of  the  copper  begins  immediately ; a large  proportion  of  it  is  deposited 
on  the  platinum  in  form  of  a solid  coating ; another  portion  separates, 
more  particularly  from  concentrated  solutions,  in  the  form  of  red  spongy 
masses.  Application  of  heat,  though  it  promotes  the  reaction,  is  not  ab- 
solutely necessary ; but  there  must  always  be  sufficient  free  acid  present 
to  keep  up  the  evolution  of  hydrogen.  After  the  lapse  of  about  an  hour 
or  two,  the  whole  of  the  copper  has  separated.  To  make  sure  of  this, 
test  a small  portion  of  the  supernatant  fluid  with  sulphuretted  hydrogen 
water ; if  this  fails  to  impart  a brown  tint  to  it,  you  may  safely  assume 
that  the  precipitation  of  the  copper  is  complete.  Ascertain  now,  also, 
whether  the  zinc  is  entirely  dissolved,  by  feeling  about  for  any  hard 
lumps  with  a glass  rod,  and  observing  whether  renewed  evolution  of 
hydrogen  will  take  place  upon  addition  of  hydrochloric  acid.  If  the 
results  are  satisfactory  in  this  respect  also,  press  the  copper  together 
with  a glass  rod,  decant  the  clear  fluid,  which  is  an  easy  operation,  pour, 
without  loss  of  time,  boiling  water  into  the  dish,  decant  again,  and  repeat 
this  operation  until  the  washings  are  quite  free  from  hydrochloric  acid. 
Decant  the  water  now  as  far  as  practicable,  rinse  the  dish  with  strong- 
alcohol,  place  in  the  water-bath,  and,  when  the  copper  is  perfectly  dry, 
let  it  cool,  and  weigh.  If  you  have  no  platinum  dish,  the  precijhtation 
may  be  effected  also  in  a porcelain  crucible  or  glass  dish  ; but  it  will,  in 
that  case,  take  a longer  time,  owing  to  the  absence  of  the  galvanic  antag^ 
onism  between  platinum  and  zinc ; and  the  whole  of  the  copper  will  be 
obtained  in  loose  masses,  and  not  firmly  adhering  to  the  sides  of  the  cruci- 
ble or  dish,  as  in  the  case  of  precipitation  in  platinum  vessels. 

The  results  are  very  accurate.  The  direct  experiment,  No.  78,  gave 
100* *0  and  100*00,  instead  of  100.  Fr.  Mohr  (loc.  cit.)  obtained  equally 
satisfactory  results  by  precipitating  in  a porcelain  crucible.* 

b.  JBy  Precipitation  with  a Hypophosphite. 

The  rather  concentrated  solution  in  sulphuric  acid  (chlorine  and 
nitric  acid  must  not  be  present)  is  treated  with  excess  of  a solution  of  a 
hypophosphite  in  the  cold,  and  then  gradually  warmed  on  the  water-bath 
to  80°-90°.  The  copper  shortly  separates  in  coherent  masses  of  hydride 
of  copper.  When  the  precipitation  is  complete,  as  may  be  ascertained 
by  means  of  sulphuretted  hydrogen,  or  other  appropriate  test,  the  pre- 
cipitate is  washed  with  hot  water  by  decantation,  transferred  to  a porce- 
lain crucible,  as  described  on  p.  207,  and,  after  drying,  ignited  and  cooled 
in  a stream  of  hydrogen  gas  (fig.  47,  p.  181),  or  it  is  collected  on  a filter, 

ring  zinc  as  a precipitant,  and  sulphuretted  hydrogen  is  recommended  as  a test 
for  ascertaining  whether  the  precipitation  is  complete.  I mention  this  with 
reference  to  Fr.  Mohr’s  paper  in  the  Annal.  d.  Chem.  u.  Pharm.  96,  215,  and 
Bodemann’s  Probirkunst  von  Kerl,  Seite  220. 

* Storer  (On  the  alloys  of  copper  and  zinc,  Cambridge,  1860,  p.  47)  says  that 
the  precipitated  copper  retains  water,  but  I have  not  found  this  to  be  the  case 
(See  Expt.  No.  79). 


DETERMINATION. 


230 


[§  no. 


and,  after  calcination,  weighed  in  a close  crucible  as  oxide.  Results 
very  accurate  (Gibbs  * * * §). 

3.  Determination  as  Subsulphide  of  Copper . 

a . By  Precipitation  as  Sulphide. — Precipitate  the  copper  as  in  I,  c, 
dry,  transfer  to  a porcelain  crucible,  add  the  filter-ash  and  some  pure 
powdered  sulphur  and  ignite  strongly  in  a stream  of  hydrogen  (§  108, 
fig.  47).  It  is  advisable  to  use  a gas  blast-lamp.  The  results  are  very 
accurate  (H.  Rose  f). 

b.  By  Precipitation  as  Subsulphocyanide,  after  Rivot.  J — The  solu- 
tion should  be  as  free  as  possible  from  nitric  acid  and  free  chlorine,  and 
not  too  acid.  Add  sulphurous  or  hypophosphorous  acid  in  sufficient 
quantity,  and  then  solution  of  sulphocyanide  of  potassium.  The  copper 
precipitates  as  white  subsulphocyanide^  It  is  filtered  after  standing 
some  time,  washed  and  dried,  mixed  with  sulphur,  ignited  in  hydrogen  in 
the  apparatus  alluded  to  in  ay  and  this  ignition  with  sulphur  is  repeated 
till  the  weight  is  constant.  The  precipitate  may  also  be  collected  on  a 
weighed  filter,  dried  at  100°,  and  then  weighed.  The  experiment,  No. 
80,  conducted  in  the  latter  way,  gave  99*66  instead  of  100. 

c.  Oxide  and  suboxide  of  copper,  sulphate,  and  many  other  salts  of 
copper  may  be  directly  converted  into  subsulphide,  by  mixing  with  sul- 
phur and  igniting  in  hydrogen  as  in  a (H.  Rose,  loc.  cit .).  The  results  are 
thoroughly  satisfactory. 

4.  Volumetric  Methods. 

Of  the  numerous  proposals  under  this  head,  the  following  are  the  best. 

a.  De  Haen’s  Method.§ 

I recommend  this  method,  which  was  devised  in  my  own  laboratory,  [j 
as  more  especially  applicable  in  cases  where  small  quantities  of  copper  are 
to  be  estimated  in  an  expeditious  way.  The  method  is  based  upon  the 
fact  that,  when  a salt  of  oxide  of  copper  in  solution  is  mixed  with  iodide 
of  potassium  in  excess,  subiodide  of  copper  and  free  iodine  are  formed, 
the  latter  remaining  dissolved  in  the  solution  of  iodide  of  potassium  : 2 
(CuO,  S 0:!)-f  2 K I=Cu2  I -f-  2 (K  O,  S 03)-j-I.  Now,  by  estimating 
the  iodine  by  Bunsen’s  method,  or  with  hyposulphite  of  soda  (§  146), 
we  learn  the  quantity  of  copper,  as  1 eq.  iodine  (127)  corresponds  to  2 
eq.  copper  (63*4).  The  following  is  the  most  convenient  way  of  pro- 
ceeding. Dissolve  the  compound  of  copper  in  sulphuric  acid,  best  to  a 
neutral  solution;  a moderate  excess  of  free  sulphuric  acid,  however, 
does  not  injuriously  affect  the  process.  Dilute  the  solution,  in  a measur- 
ing flask,  to  a definite  volume  ; 100  c.  c.  should  contain  from  1 to  2 grms. 
oxide  of  copper.  Introduce  now  about  10  c.  c.  of  iodide  of  potassium  so- 
lution (1  iodide  of  potassium  in  10  water)  into  a large  beaker,  add  10  c.  c. 
ofithe  copper  solution,  mix,  and  then  proceed  without  delay  to  determine 

* Am.  Joum.  Sci.  2d  Ser.  xliv.  210. 

f Compt.  rend.  38,  868;  Journ.  f.  prakt.  Chem.  62,  252. 

t Pogg.  Annal.  110,  138. 

§ Annal.  d.  Chem.  u.  Pharm.  91,  237. 

| Brown  (Quart.  Joum.  of  the  Chem  Soc.  x.  65),  who  published  this  as  a new 
method  in  1857,  must  have  been  ignorant  of  its  previous  publication  in  1854. 
The  little  variation,  too,  of  determining  the  iodine  with  hyposulphite  of  soda  (ac- 
cording to  Schwarz)  instead  of  with  sulphurous  acid  (according  to  Bunsen), 
may  be  found  in  Mohr’s  Lehrbuch  der  Titrirmethode,  i.  387  (1855) 


119.] 


OXIDE  OF  COPPER. 


231 


the  separated  iodine  by  means  of  hyposulphite  of  soda  (§146).  It  is 
scarcely  necessary  to  mention  that  the  copper  solution  must  be  free 
from  sesquioxide  of  iron  and  other  bodies  which  decompose  iodide 
of  potassium,  also  free  nitric  acid,  and  free  hydrochloric  acid.  With 
strict  attention  to  these  rules,  the  results  are  accurate.  De  Haen 
obtained,  for  instance,  0* * * §3567  instead  of  0*3566  of  sulphate  of  copper, 
99*89  and  100*1  instead  of  100  of  metallic  copper.  Further  experi- 
ments (No.  81)  have  convinced  me,  however,  that,  though  the  results 
attainable  by  this  method  are  satisfactory,  they  are  not  always  quite  so 
accurate  as  would  be  supposed  from  the  above  figures  given  by  De  Haen. 
Acting  upon  Fr.  Mohr’s  suggestion,  I tried  to  counteract  the  injurious 
influence  of  the  presence  of  nitric  acid,  by  adding  to  the  solution  con- 
taining nitric  acid  first  ammonia  in  excess,  then  hydrochloric  acid  to 
slight  excess ; the  result  was  by  no  means  satisfactory.  The  reason  of 
this  is  that  a solution  of  nitrate  of  ammonia,  mixed  with  some  hydro- 
chloric acid,  will,  even  after  a short  time,  begin  to  liberate  iodine  from 
solution  of  iodide  of  potassium. 

b.  Carl  Mohr’s  Method  ; H.  Fleck’s  Modification.* 

The  proposal  to  take  the  action  of  solution  of  cyanide  of  potassium  on 
ammoniacal  solution  of  copper  as  the  foundation  of  a method  for  estima- 
ting copper  is  due  to  Carl  MoHR.f 

The  azure-blue  color  disappears,  Cu2  Cy,  N H4  Cy  and  K O are  formed, 
while  1 eq.  cyanogen  is  separated,  which,  acting  on  the  free  ammonia, 
gives  urea,  oxalate  of  urea,  cyanide  of  ammonium  and  formiate  of  ammo- 
nia (Liebig  J). 

The  decomposition  is  not  always  the  same,  the  quantity  and  degree  of 
concentration  of  the  ammonia  has  a marked  influence  on  it,  comp.  Liebig 
( loc . cit .),  also  my  own  experiments  (No.  82,  a),  from  which  it  appears  that 
neutral  ammonia  salts  also  affect  the  results. 

Fleck  (loc.  cit.)  proposes  the  following  modification  : — 

Instead  of  caustic  ammonia  use  a solution  of  sesquicarbonate  of  ammo- 
nia (1  in  10),  warm  the  mixture  to  about  60°,  and  in  order  to  render  the 
end-reaction  plainer  add  2 drops  of  solution  of  ferrocyanide  of  potassium 
(1  in  20) ; the  blue  color  of  the  solution  is  not  altered  by  this  addition,  nor 
is  its  clearness  affected.  The  value  of  the  cyanide  of  potassium  solution 
is  first  determined,  by  means  of  copper  solution  of  known  strength,  and 
it  is  then  employed  on  the  copper  solution  to  be  examined.  On  dropping 
the  cyanide  of  potassium  into  the  blue  solution  warmed  to  60°,  the  odor 
of  cyanogen  is  plainly  perceptible,  and  the  color  gradually  disappears. 
As  soon  as  the  ammoniacal  double  salt  of  copper  is  destroyed,  the  solution 
becomes  red  from  the  formation  of  ferrocyanide  of  copper,  without  any 
precipitate  appearing,  and  with  the  addition  of  a final  drop  of  cyanide 
of  potassium  this  red  color  in  its  turn  vanishes,  so  that  the  fluid  now  ap- 
pears quite  colorless. 

The  method  thus  modified  yields,  it  is  true,  better,  but  still  only  ap- 
proximate, results. § Where  such  are  good  enough,  the  method  is  certainly 

* Polytechn.  Centralbl  1859,  1313. 

f Annal.  d.  Chem.  u.  Pharm.  94, 198  ; Fr.  Mohr’s  Lehrbuch  der  Titrirmethode, 
2,  91. 

% Annal.  d.  Chem.  u.  Pharm.  95,  118. 

§ In  six  experiments,  in  which  he  had  purposely  added  different  quantities  of 
carbonate  of  ammonia,  Fleck  used  for  100  c.  c.  copper  solution,  in  the  minimum 
15*2,  in  the  maximum  15*75,  in  the  mean  15*46  c.  c.  cyanide  of  potassium  solution. 


232 


DETERMINATION. 


[§  120. 

convenient.  I have  found  that  the  presence  of  ammonia  salts  is  here  also 
not  without  influence  (Expt.  No.  82,  b) ; on  this  account  the  method  seems 
to  be  applicable  only,  if  the  standardizing  of  the  cyanide  of  potassium 
and  the  actual  analyses  are  performed  under  very  similar  circumstances. 


§ 120. 

6.  Teroxide  of  Bismuth. 

a.  Solution . 

Metallic  bismuth,  the  teroxide,  and  all  other  compounds  of  that  metal, 
are  dissolved  best  in  nitric  acid,  more  or  less  diluted.  It  must  be  borne 
in  mind  that  hydrochloric  acid  solutions  of  bismuth,  if  concentrated, 
cannot  be  evaporated  without  loss  of  chloride  of  bismuth. 

b.  Determination. 

Bismuth  is  weighed  in  the  form  of  teroxide , of  chromate , of  sulphide , 
or  in  the  metallic  state.  The  compounds  of  bismuth  are  converted  into 
teroxide  by  ignition,  by  precipitation  as  basic  carbonate,  or  by  repeated 
evaporation  of  the  nitrate  solution.  These  are  sometimes  preceded  by 
separation  as  sulphide.  The  determination  as  metallic  bismuth  is  fre- 
quently preceded  by  precipitation  as  sulphide  or  as  basic  chloride. 

We  may  convert  into 

1.  Teroxide  of  Bismuth. 

a.  By  Precipitation  as  Carbonate  of  Teroxide  of  Bismuth. 

All  compounds  of  bismuth  which  dissolve  in  nitric  acid  to  nitrate,  no 
other  acid  remaining  in  the  solution. 

b.  By  Ignition. 

a.  Salts  of  bismuth  with  readily  volatile  oxygen  acids. 

Q.  Salts  of  bismuth  with  organic  acids. 

c.  By  Evaporation. 

Bismuth  in  nitric  acid  solution. 

d.  By  Precipitation  as  Tersulpliide  of  Bismuth. 

All  compounds  of  bismuth  without  exception. 

2.  Chromate  of  Teroxide  of  Bismuth. 

All  compounds  named  in  1,  a. 

3.  Sulphide  of  Bismuth. 

The  compounds  of  bismuth  without  exception. 

4.  Basic  Chloride  of  Bismuth. 

All  compounds  of  bismuth. 

5.  Metallic  Bismuth. 

The  oxide  and  its  salts,  the  sulphide,  and  the  basic  chloride. 


233 


§ 120.]  TEROXIDE  OF  BISMUTH. 

1.  Determination  of  Pismuth  as  Ter  oxide. 

a.  Py  Precipitation  as  Carbonate  of  Teroxide  of  Pismuth. 

Mix  the  solution  of  bismuth  with  carbonate  of  ammonia  in  very  slight 

excess,  and  heat  for  some  time  nearly  to  boiling ; filter,  dry  the  precipi- 
tate, and  ignite  in  the  manner  directed  § 116,  1 (Ignition  of  carbonate  of 
lead)  ; the  process  of  ignition  serves  to  convert  the  carbonate  into  the 
pure  teroxide  of  bismuth.  Should  the  solution  be  too  concentrated,  dilute 
with  water,  previously  to  the  addition  of  carbonate  of  ammonia ; whether 
the  dilution  leads  to  the  precipitation  of  basic  nitrate  of  bismuth  or  not, 
is  a matter  of  perfect  indifference.  For  the  properties  of  the  precijntate 
and  residue,  see  § 86. 

The  method  gives  accurate  results,  though  generally  a trifle  too  low, 
owing  to  the  circumstance  that  carbonate  of  teroxide  of  bismuth  is  not 
absolutely  insoluble  in  carbonate  of  ammonia. 

Were  you  to  attempt  to  precipitate  bismuth,  by  means  of  carbonate  of 
ammonia,  from  solutions  containing  sulphuric  acid  or  hydrochloric  acid, 
you  would  obtain  incorrect  results,  since  with  the  basic  carbonate, 
basic  sulphate  or  basic  chloride  would  be  precipitated,  which  are  not 
decomposed  by  excess  of  carbonate  of  ammonia.  Were  you  to  filter 
off  the  precipitate  without  warming,  a considerable  loss  would  be  sus- 
tained, as  the  whole  of  the  basic  carbonate  would  not  have  been  separated 
(Expt.  No.  83). 

b.  Py  Ignition. 

a..  Compounds  like  the  carbonate  or  nitrate  of  teroxide  of  bismuth  are 
ignited  in  a porcelain  crucible  until  their  weight  remains  constant. 

fi.  Compounds  of  teroxide  of  bismuth  with  organic  acids  are  treated 
like  the  corresponding  compounds  of  oxide  of  copper  (§  119,  1,  d). 

c.  Py  Evaporation. 

The  solution  of  the  nitrate  is  evaporated,  in  a porcelain  dish  on  the 
water-bath,  till  the  neutral  salt  remains  in  syrupy  solution  ; — add  water, 
loosen  the  white  crust  that  is  formed  with  a glass  rod  from  the  sides,  eva- 
porate again  on  a water-bath,  reprecipitate  with  water,  and  repeat  the 
whole  operation  three  or  four  times.  After  the  dry  mass  on  the  water- 
bath  has  ceased  to  smell  of  nitric  acid,  it  is  allowed  to  cool  thoroughly, 
and  then  treated  with  cold  water  containing  a little  nitrate  of  ammonia 
(1  in  500)  ; after  the  residue  and  fluid  have  been  a short  time  together, 
filter,  wash  with  the  weak  solution  of  nitrate  of  ammonia,  dry  and  ignite 
(§  53).  Results  very  satisfactory  (J.  Lowe  *). 

d.  Py  Precipitation  as  Tersulphide  of  Pismuth. 

Dilute  the  solution  with  water  slightly  acidulated  with  acetic  acid  (to 
pre  vent  the  precipitation  of  a basic  salt),  and  precipitate  with  sulphuretted 
hydrogen  water  or  gas  ; allow  the  precipitate  to  subside,  and  test  a portion 
of  the  supernatant  fluid  with  sulphuretted  hydrogen  water  y if  it  remains 
clear,  which  is  a sign  that  the  bismuth  is  completely  precipitated,  filter  (the 
filtrate  should  smell  strongly  of  H S),  and  wash  the  precipitate  with  water 
containing  sulphuretted  hydrogen.  Or  mix  with  ammonia  until  the  free 
acid  is  neutralized,  and  then  add  sulphide  of  ammonium  in  excess. 

The  washed  precipitate  may  now  be  weighed  in  three  different  forms, 
viz.,  as  sulphide,  as  metal,  or  as  oxide.  The  treatment  in  the  two  former 


Joum.  f.  prakt.  Chem.  74,  344. 


DETERMINATION. 


234 


L§  120. 


cases  will  be  described  in  3 and  5 : in  the  latter  case  proceed  as 
follows  : — 

Spread  the  filter  out  on  a glass  plate  and  remove  the  precipitate  to  a 
vessel  by  means  of  a jet  of  water  from  the  wash-bottle — or,  if  this  is  not 
practicable,  put  the  precipitate  and  filter  together  into  the  vessel — and 
heat  gently  with  moderately  strong  nitric  acid  until  complete  decomposi- 
tion is  effected  ; the  solution  is  then  diluted  with  water  slighly  acidulated 
with  acetic  or  nitric  acid,  and  filtered,  the  filter  being  washed  with  the 
acidulated  water ; the  filtrate  is  then  finally  precipitated  as  directed  in  a. 

2.  Determination  of  Dismuth  as  Chromate  of  Teroxide.  ( J.  Lowe.  *) 

Pour  the  solution  of  teroxide  of  bismuth,  which  must  be  as  neutral  as 

possible,  and  must,  if  necessary,  be  first  freed  from  the  excess  of  nitric 
acid  by  evaporation  on  the  water-bath,  into  a warm  solution  of  pure 
bichromate  of  potassa  in  a porcelain  dish,  with  stirring,  and  take  care  to 
leave  the  alkaline  chromate  slightly  in  excess.  Rinse  the  vessel  which 
contained  the  solution  of  bismuth  with  water  containing  nitric  acid  into 
the  porcelain  dish.  The  precipitate  formed  must  be  orange-yellow,  and 
dense  throughout ; if  it  is  flocculent,  and  has  the  color  of  the  yolk  of  an 
egg,  this  is  a sign  that  there  is  a deficiency  of  chromate  of  potassa ; in 
which  case  add  a fresh  quantity  of  this  salt,  taking  care,  however,  to  guard 
against  too  great  an  excess,  and  boil  until  the  precipitate  presents  the 
proper  appearance.  Boil  the  contents  of  the  dish  for  ten  minutes,  with 
stirring ; then  wash  the  precipitate,  first  by  repeated  boiling  with  water 
and  decantation  on  to  a weighed  filter,  at  last  thoroughly  on  the  latter 
with  boiling  water;  dry  at  about  120°,  and  weigh.  For  the  pro- 
perties and  composition  of  the  precipitate,  see  § 86.  Results  very 
satisfactory. 

3.  Determination  of  Dismuth  as  Sulphide. 

Precipitate  the  bismuth  as  sulphide  according  to  1,  d.  If  the  precipi- 
tate contains  sulphur,  extract  the  later  by  boiling  with  solution  of  sulphite 
of  soda,  or  by  treatment  with  bisulphide  of  carbon  (compare  the  determi- 
nation of  mercury  as  sulphide,  § 118,  3),  collect  on  a weighed  filter,  dry 
at  100°,  and  weigh. 

The  drying  must  be  conducted  with  caution.  At  first  the  precipitate 
loses  weight,  by  the  evaporation  of  water,  then  it  gains  weight,  from  the 
absorption  of  oxygen.  Hence  you  should  weigh  every  half-hour,  and 
take  the  lowest  weight  as  the  correct  one.  Compare  Expt.  No.  58. 
Properties  and  composition,  § 86,  e. 

The  sulphide  of  bismuth  cannot  be  conveniently  converted  into  the 
metallic  state  by  ignition  in  hydrogen,  as  its  complete  decomposition  is  a 
work  of  considerable  time.  As  regards  reduction  with  cyanide  of  potas- 
sium, see  5. 

4.  Precipitation  of  Dismuth  as  Dasic  Chloride. 

The  precipitation  of  bismuth  as  basic  chloride,  and  the  reduction  of  the 
latter  with  cyanide  of  potassium,  is  recommended  by  H.  RosE.f  The  pro- 
cess is  conducted  as  follows : — nearly  neutralize  any  large  excess  of  acid 
that  may  be  present  with  potassa,  soda,  or  ammonia,  add  chloride  of 
sodium  in  sufficient  quantity  (if  hydrochloric  acid  is  not  already  present), 
and  then  a rather  large  quantity  of  water.  After  allowing  to  stand  some 


Journ.  f.  prakt.  Chem.  67,  464. 


f Pogg.  Annal.  110,  425. 


§ 121.] 


OXIDE  OF  CADMIUM. 


235 


time,  test  whether  a portion  of  the  clear  supernatant  fluid  is  rendered 
turbid  by  a further  addition  of  water ; and  then,  if  required,  add  water 
to  the  whole  till  the  precipitation  is  complete.  Finally,  filter  the  pre- 
cipitate, wash  completely  with  cold  water,  dry  and  fuse  with  cyanide  of 
potassium  as  directed  below  (5).  Results  accurate. 

5.  Determination  of  Bismuth  as  Metal. 

The  oxide,  sulphide,  or  basic  chloride  that  are  to  be  reduced  are  fused 
in  a large  porcelain  crucible  with  five  times  their  quantity  of  ordinary 
cyanide  of  potassium.  In  the  case  of  oxide  and  basic  chloride,  the  re- 
duction is  completed  in  a short  time  at  a gentle  heat ; sulphide,  on  the 
other  hand,  requires  longer  fusion  and  a higher  temperature.  The  ope- 
ration has  been  successful,  if  on  treatment  with  water  metallic  grains 
are  obtained.  These  grains  are  first  washed  completely  and  rapidly  with 
water,  then  with  weak,  and  lastly  with  strong  spirit,  dried  and  weighed. 
If  you  have  been  reducing  the  sulphide,  and  on  treating  the  fused  mass 
with  water  a black  powder  (a  mixture  of  bismuth  with  sulphide  of  bis- 
muth) is  visible,  besides  the  metallic  grains,  it  is  necessary  to  fuse  the 
former  again  with  cyanide  of  potassium. 

It  sometimes  happens  that  the  crucible  is  attacked,  and  particles  of 
porcelain  are  found  mixed  with  the  metallic  bismuth ; to  prevent  this  from 
spoiling  the  analysis,  weigh  the  crucible  together  with  a small  dry  filter 
before  the  experiment,  collect  the  metal  on  the  filter,  dry  and  weigh  the 
crucible  with  the  filter  and  bismuth  again.  Results  good  (H.  Rose  *). 

§ 121. 

7.  Oxide  of  Cadmium. 

a.  Solution. 

Cadmium,  its  oxide,  and  all  the  other  compounds  insoluble  in  water, 
are  dissolved  in  hydrochloric  acid  or  in  nitric  acid. 

b.  Determination. 

Cadmium  is  weighed  either  in  the  form  of  oxide , or  in  that  of  sulphide 

(§  87). 

We  may  convert  into 

1.  Oxide  of  Cadmium. 


a.  By  Precipitation. 

The  compounds  of  cadmium 
which  are  soluble  in  water;  the 
insoluble  compounds,  the  acid  of 
which  is  removed  upon  solution 
in  hydrochloric  acid  ; salts  of  cad- 
mium with  organic  acids. 


b.  By  Ignition. 

Salts  of  cadmium  with  readily 
volatile  or  easily  decomposable  in- 
organic oxygen  acids. 


2.  Sulphide  of  Cadmium. 


All  compounds  of  cadmium  without  exception. 

1.  Determination  as  Oxide  of  Cadmium, 
a.  By  Precipitation. 

Precipitate  with  carbonate  of  soda  or  potassa,  wash  the  precipitated 


* Pogg.  Annal.  91,  104,  and  110,  136. 


236 


DETERMINATION. 


[§  122. 

carbonate  of  cadmium,  and  convert  it,  by  ignition,  into  the  state  of  pure 
oxide.  The  precipitation  is  conducted  as  in  the  case  of  zinc,  § 108,  1,  a. 
The  oxide  of  cadmium  which  adheres  to  the  filter  may  easily  be  reduced 
and  volatilized  ; it  is  therefore  necessary  to  be  cautious.  In  the  first 
place  choose  a thin  filter,  transfer  the  dried  precipitate  as  completely  as 
possible  to  the  crucible,  replace  the  filter  in  the  funnel,  and  moisten  it 
with  nitrate  of  ammonia  solution,  allow  to  dry,  and  then  burn  carefully  in 
a coil  of  platinum  wire.  Let  the  ash  fall  into  the  crucible  containing  the 
mass  of  the  precipitate,  ignite  carefully,  avoid  the  action  of  reducing 
gases,  and  finally  weigh.  For  the  properties  of  the  precipitate  and  the 
residue,  see  § 87.  Results  good. 

b.  JBy  Ignition. 

Same  process  as  for  zinc,  § 108,  1,  c. 

2.  Determination  as  Sulphide  of  Cadmium. 

Neutral  or  acid  solutions  are  precipitated  with  sulphuretted  hydrogen 
water  or  gas,  which  must  be  used  in  sufficient  excess.  The  presence  of  a 
considerable  quantity  of  free  hydrochloric  or  nitric  acid  may — especially 
if  the  solution  is  not  enough  diluted — prevent  complete  precipitation, 
hence  such  an  excess  should  be  avoided,  and  the  clear  supernatant  fluid 
should  in  all  cases  be  tested,  by  the  addition  of  a relatively  large  amount  of 
sulphuretted  hydrogen  water  to  a portion,  before  being  filtered.  Alkaline 
solutions  of  cadmium  may  be  precipitated  with  sulphide  of  ammonium. 
If  the  sulphide  of  cadmium  is  free  from  admixed  sulphur,  it  may  be  at 
once  collected  on  a weighed  filter,  dried  at  100°,  and  weighed  ; if,  on  the 
contrary,  it  contains  free  sulphur,  it  may  be  purified  by  boiling  with  a 
solution  of  sulphite  of  soda,  or  by  treatment  with  bisulphide  of  carbon 
(see  Sulphide  of  mercury,  § 118,  3).  Results  accurate.  The  precipita- 
tion of  sulphur  may  occasionally  be  obviated  by  adding  to  the  cadmium 
solution  cyanide  of  potassium  till  the  precipitate  first  formed  is  redissolved, 
and  then  precipitating  this  solution  with  sulphuretted  hydrogen. 

If  the  sulphide  of  cadmium  is  not  to  be  weighed  as  such,  warm  it,  to- 
gether with  the  filter,  with  moderately  strong  hydrochloric  acid,  till  the 
precipitate  has  dissolved  and  the  odor  of  sulphuretted  hydrogen  is  no 
longer  perceptible,  filter  and  precipitate  the  solution  as  in  1,  a,  after  hav- 
ing removed  the  excess  of  free  acid  for  the  most  part  by  evaporation. 

Supplement  to  the  Fifth  Group. 

§ 122. 

8.  Protoxide  of  Palladium. 

Protoxide  of  palladium  is  converted,  for  the  purpose  of  estimation,  into 
the  metallic  state  / or — in  many  separations — into  double  chloride  of  pal- 
ladium  and  potassium. 

1.  Determination  as  Palladium. 

a.  Neutralize  the  solution  of  protochloride  of  palladium  almost  com- 
pletely with  carbonate  of  soda,  mix  with  a solution  of  cyanide  of  mercury ; 
and  digest  the  mixture  for  some  time.  A yellowish-white  precipitate  of 
protocyanide  of  palladium  will  subside ; from  dilute  solutions,  only  after 
the  lapse  of  some  time.  Wash  this  precipitate,  dry,  and  ignite  ; weigh 


§ 123.] 


TEROXIDE  OF  GOLD. 


237 


the  reduced  metal  obtained.  If  the  solution  contains  nitrate  of  protoxide, 
evaporate  it  first  with  hydrochloric  acid  to  dryness ; as  otherwise  the  pre- 
cipitate obtained  deflagrates  upon  ignition  (Wollaston). 

b.  Mix  the  solution  of  the  protochloride  or  nitrate  of  protoxide  of 
palladium  with  formiate  of  soda  or  potassa,  and  warm  until  no  more 
carbonic  acid  escapes.  The  palladium  precipitates  in  brilliant  scales 
(Dobereiner). 

c.  Precipitate  the  acid  solution  of  palladium  with  sulphuretted  hydro- 
gen, filter,  wash  with  boiling  water,  roast,  and  either  convert  the  basic 
sulphate  of  protoxide  of  palladium  formed  into  pure  metal,  by  ignition 
over  the  blast  gas-lamp,  pr  dissolve  it  in  hydrochloric  acid,  and  precipitate 
as  in  a. 

Exposed  to  a moderate  red  heat  metallic  palladium  becomes  covered 
with  a film  varying  from  violet  to  blue,  but  at  a higher  temperature  it 
recovers  its  lustre  ; this  tarnishing  and  recovery  of  the  metallic  lustre 
is  not  attended  with  any  perceptible  difference  of  weight.  Palladium 
requires  the  very  highest  degree  of  heat  for  its  fusion.  It  dissolves  readily 
in  nitrohydrochloric  acid,  with  difficulty  in  pure  nitric  acid,  more  easily 
in  nitric  acid  containing  nitrous  acid,  with  difficulty  in  boiling  con- 
centrated sulphuric  acid. 

2.  Determination  as  Double  Chloride  of  Palladium  and  Potassium. 

Evaporate  the  solution  of  chloride  of  palladium  with  chloride  of 
potassium  and  nitric  acid  to  dryness,  and  treat  the  mass  when  cold 
with  alcohol  of  *833  sp.  gr.,  in  which  the  double  salt  is  insoluble.  Col- 
lect on  a weighed  filter,  dry  at  100°,  and  weigh.  Results  a little  too 
low,  as  traces  of  the  double  salt  pass  away  with  the  alcohol  washings 
(Berzelius). 

The  double  chloride  of  palladium  and  potassium  consists  of  micro- 
scopic octahedra ; it  presents  the  appearance  of  a vermilion,  or,  if  the 
crystals  are  somewhat  larger,  of  a brown  powder.  It  is  very  slightly 
soluble  in  cold  water  ; it  is  almost  insoluble  in  cold  spirit  of  the  above 
strength.  It  contains  26*701^  palladium. 

SIXTH  GROUP. 

Teroxide  of  Gold — Binoxide  of  Platinum — Teroxide  of  Anti- 
mony— Binoxide  of  Tin — Protoxide  of  Tin — Arsenious  and  Arsenic 
Acids — (Molybdic  Acid). 

§123. 

1.  Teroxide  of  Gold. 

a.  Solution. 

Metallic  gold,  and  all  compounds  of  gold  insoluble  in  water,  are  warmed 
with  hydrochloric  acid,  and  nitric  acid  is  gradually  added  until  complete 
solution  is  effected  ; or  they  are  repeatedly  digested  with  strong  chlorine 
water.  The  latter  method  is  resorted  to  more  especially  in  cases  where 
the  quantity  of  gold  to  be  dissolved  is  small,  and  mixed  with  foreign 
oxides,  which  it  is  wished  to  leave  undissolved. 

b.  Determination. 

Gold  is  always  weighed  in  the  metallic  state , The  compounds  are 


238 


DETERMINATION. 


brought  into  this  form,  either  by  ignition  or  by  precipitation,  as  gold,  or 
sulphide  of  gold.  See  Cupellation,  § 

We  convert  into 

Metallic  Gold. 

a.  JBy  Ignition,  b.  Py  Precipitation  as  Metallic 

Gold. 

All  compounds  of  gold  which  All  compounds  of  gold  without 
contain  no  fixed  acid.  exception  in  cases  where  a is  inap- 

plicable. 

c.  j By  Precipitation  as  TersulpTiide  of  Gold. 

This  method  serves  to  effect  the  separation  of  gold  from  certain  other 
metals  which  may  be  mixed  with  it  in  a solution. 

Determination  as  Metallic  Gold. 

a.  Py  Ignition. 

Heat  the  compound,  in  a covered  porcelain  crucible,  very  gently  at 
first,  but  finally  to  redness,  and  weigh  the  residuary  pure  gold.  For 
properties  of  the  residue,  see  § 88.  The  results  are  most  accurate. 

b.  Py  Precipitation  as  Metallic  Gold. 

a.  The  solution  is  free  from  Nitric  Acid. 

Mix  the  solution  with  a little  hydrochloric  acid,  if  it  does  not  already 
contain  some  of  that  acid  in  the  free  state,  and  add  a clear  solution  of 
sulphate  of  protoxide  of  iron  in  excess  ; heat  gently  for  a few  hours 
until  the  precipitated  fine  gold  powder  has  completely  subsided ; filter, 
wash,  dry,  and  ignite  according  to  § 52.  A porcelain  dish  is  a more 
appropriate  vessel  to  effect  the  precipitation  in  than  a beaker,  as  the 
heavy  fine  gold  powder  is  more  readily  rinsed  out  of  the  former  than 
out  of  the  latter.  The  results  are  accurate. 

j8.  The  solution  of  Gold  contains  Nitric  Acid. 

Evaporate  the  solution,  on  a water-bath,  to  the  consistence  of  syrup, 
adding  from  time  to  time  hydrochloric  acid ; dissolve  the  residue  in  water 
containing  hydrochloric  acid,  and  treat  the  solution  as  directed  in  a.  It 
will  sometimes  happen  that  the  residue  does  not  dissolve  to  a clear  fluid, 
in  consequence  of  a partial  decomposition  of  the  terchloride  of  gold 
into  protochloride  and  metallic  gold  ; however,  this  is  a matter  of  per- 
fect indifference. 

y.  In  cases  where  it  is  wished  to  avoid  the  presence  of  iron  in  the 
filtrate,  the  gold  may  be  reduced  by  means  of  oxalic  acid.  To  this  end, 
the  dilute  solution — freed  previously,  if  necessary,  from  nitric  acid, 
in  the  manner  directed  in  j3 — is  mixed,  in  a beaker,  with  oxalic  acid,  or 
with  oxalate  of  ammonia  in  excess,  some  hydrochloric  acid  added  (if  that 
acid  is  not  already  present  in  the  free  state),  and  the  vessel,  covered  with 
a glass  plate,  is  kept  standing  for  two  days  in  a moderately  warm  place. 
At  the  end  of  that  time,  the  whole  of  the  gold  will  be  found  to  have 
separated  in  small  yellow  scales,  which  are  collected  on  a filter,  washed, 
dried,  and  ignited.  If  the  gold  solution  contains  a large  excess  of  hydro- 


BINOXIDE  OF  PLATINUM. 


239 


§ 124.] 

chloric  acid,  the  latter  should  be  for  the  most  part  evaporated,  before  the 
solution  is  diluted  and  the  oxalic  acid  added.  If  the  gold  solution  con- 
tains chlorides  of  alkali  metals,  it  is  necessary  to  dilute  largely,  and 
allow  to  stand  for  a long  time,  in  order  to  effect  complete  precipitation 
(H.  Rose). 

c.  By  Precipitation  as  Tersulphide  of  Gold. 

Sulphuretted  hydrogen  gas  is  transmitted  in  excess  through  the  dilute 
solution ; the  precipitate  formed  is  speedily  filtered  off,  without  heating, 
washed,  dried,  and  ignited  in  a porcelain  crucible.  For  the  properties 
of  the  precipitate,  see  § 88.  The  results  are  accurate. 


§124. 

2.  Binoxide  of  Platinum. 


a.  Solution. 

Metallic  platinum,  and  the  compounds  of  platinum  which  are  insolu- 
ble in  water,  are  dissolved  by  digestion,  at  a gentle  heat,  with  nitrohy- 
drochloric  acid. 

b.  Determination . 

Platinum  is  invariably  weighed  in  the  metallic  state , to  which  con- 
dition its  compounds  are  brought,  either  by  precipitation  as  bichloride 
of  platinum  and  chloride  of  ammonium,  bichloride  of  platinum  and 
chloride  of  potassium,  or  bisulphide  of  platinum,  or  by  ignition,  or  by 
precipitation  with  reducing  agents.  All  compounds  of  platinum,  with- 
out exception,  may,  in  most  cases,  be  converted  into  platinum  by  either 
of  these  methods.  Which  is  the  most  advantageous  process  to  be  pur- 
sued in  special  instances,  depends  entirely  upon  the  circumstances.  The 
reduction  of  compounds  of  platinum  to  the  metallic  state  by  simple  igni- 
tion is  preferable  to  the  other  methods,  in  all  cases  where  its  applica- 
tion is  admissible.  The  precipitation  as  bisulphide  of  platinum  is 
resorted  to  exclusively  to  effect  the  separation  of  platinum  from  other 
metals. 

Determination  as  Metallic  Platinum. 

a.  By  Precipitation  as  Bichloride  of  Platinum  and  Chloride  of  Am- 
monium. 

The  solution  must  be  concentrated  if  necessary  by  evaporation  on  a 
water-bath.  Mix,  in  a beaker,  with  ammonia  until  the  excess  of  acid 
(that  is,  supposing  an  excess  of  acid  to  be  present)  is  nearly  saturated  ; 
add  chloride  of  ammonium  in  excess,  and  mix  the  fluid  with  a pretty 
large  quantity  of  absolute  alcohol. 

Cover  the  beaker  now  with  a glass  plate,  and  let  it  stand  for  twenty- 
four  hours,  after  which  filter  on  an  unweighed  filter,  wash  the  precipi- 
tate with  spirit  of  wine  of  about  80  per  cent.,  till  the  substances  to  be 
separated  are  removed,  and  dry  carefully. 

Introduce  the  dry  precipitate,  wrapped  up  in  the  filter,  into  a weighed 
porcelain  crucible,  put  on  the  lid,  and  apply  a very  gentle  heat  for  some 
time,  until  no  more  fumes  of  chloride  of  ammonium  escape ; now  remove 
the  lid,  place  the  crucible  obliquely  (§  52),  and  let  the  filter  burn.  Ap- 


240 


DETERMINATION. 


[§  124. 


ply  finally  an  intense  heat  for  some  time,  and  then  weigh.  In  the  case 
of  large  quantities  this  final  ignition  is  advantageously  conducted  in 
a stream  of  hydrogen  (§  108,  fig.  47,  p.  181),  or  with  addition  of  oxalic 
acid,  in  order  to  be  quite  sure  of  effecting  complete  decomposition.  For 
the  properties  of  the  precipitate  and  residue,  see  § 89.  The  results  are 
satisfactory,  though  generally  a little  too  low,  as  the  bichloride  of  plati- 
num and  chloride  of  ammonium  is  not  altogether  insoluble  in  spirit  of 
wine  (Expt.  No.  16) ; and  as  the  fumes  of  chloride  of  ammonium 
evolved  during  the  first  stage  of  the  process  of  ignition  are  liable  to 
carry  away  traces  of  the  yet  undecomposed  double  chloride,  if  the  appli- 
cation of  heat  is  not  conducted  with  the  greatest  possible  care. 

If  the  precipitated  bichloride  of  platinum  and  chloride  of  ammonium 
were  weighed  in  that  form,  the  results  would  be  inaccurate,  since,  as  I 
have  convinced  myself  bv  direct  experiments,  it  is  impossible  to  com- 
pletely free  the  double  chloride,  by  washing  with  spirit  of  wine,  from  all 
traces  of  the  chloride  of  ammonium  thrown  down  in  conjunction  with  it, 
without  dissolving,  at  the  same  time,  a considerable  portion  of  the  double 
chloride.  As  a general  rule,  the  results  obtained  by  weighing  the  bichlo- 
ride of  platinum  and  chloride  of  ammonium  in  that  form  are  one  or  two 
per  cent,  too  high. 

b.  By  Precipitation  as  Bichloride  of  Platinum  and  Chloride  of 
Potassium. 

Mix  the  solution  of  the  compound  under  examination  in  a beaker, 
with  potassa,  until  the  greater  part  of  the  excess  of  acid  (if  there  be 
any)  is  neutralized  ; add  chloride  of  potassium  slightly  in  excess,  and 
finally  a pretty  large  quantity  of  absolute  alcohol ; should  your  solu- 
tion of  platinum  be  very  dilute,  you  must  concentrate  it  previously  to 
the  addition  of  the  alcohol.  After  twenty  hours,  collect  the  precipitate 
upon  a weighed  filter,  wash  with  spirit  of  wine  of  70  per  cent.,  dry 
thoroughly  at  100°,  and  weigh.  Now  put  a portion  of  the  dried  precipi- 
tate into  a weighed  bulb-tube,  and  clean  the  tube  part  of  the  latter  with 
a feather ; then  weigh  the  tube  again,  to  ascertain  the  exact  amount 
of  bichloride  of  platinum  and  chloride  of  potassium  which  it  contains. 
Connect  the  tube  now  with  an  apparatus  evolving  dry  hydrogen  gas,  and 
heat  its  contents  to  redness,  until  no  more  hydrochloric  acid  fumes  are 
evolved,  which  you  may  readily  ascertain  by  holding  a glass  rod  moist- 
ened with  ammonia  to  the  opening  of  the  tube.  Allow  to  cool,  remove 
the  tube  from  the  apparatus,  fill  it  with  water,  decant  the  solution  of 
chloride  of  potassium  cautiously,  wash  the  residuary  platinum  carefully, 
dry  the  tube  thoroughly  (by  heating  it  in  the  stream  of  hydrogen  gas), 
and  weigh.  Subtract  from  the  weight  found  the  original  w*eight  of  the 
empty  tube,  and  calculate  from'  the  remainder  (the  weight  of  the  residu- 
ary platinum  in  the  tube)  the  amount  of  platinum  contained  in  the 
whole  precipitate. 

For  the  properties  of  the  precipitate  and  residue,  see  § 89. 

The  results  are  more  accurate  than  those  obtained  by  method  a,  since, 
on  the  one  hand,  the  bichloride  of  platinum  and  chloride  of  potassium  is 
more  insoluble  in  spirit  of  wine  than  the  corresponding  ammonium  salt ; 
and,  on  the  other  hand,  loss  of  substance  is  less  likely  to  arise  during 
the  process  of  ignition  than  is  the  case  in  method  a.  The  results  would 
be  less  accurate  were  the  ignition  effected  simply  in  a crucible,  instead  of 
in  a current  of  hydrogen  gas,  since  in  that  case  complete  decomposition 


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§ 125.] 


TEROXIDE  OF  ANTIMONY. 


241 


will  not  ensue,  at  all  events  not  if  the  amount  of  substance  acted  upon 
is  at  all  considerable.  To  weigh  the  bichloride  of  platinum  and  chloride 
of  potassium  in  that  form  would  not  be  practicable,  as  it  is  impossible  to 
remove,  by  washing  with  spirit  of  wine,  all  traces  of  the  chloride  of  potas- 
sium thrown  down  along  with  it,  without  at  the  same  time  dissolving  a 
portion  of  the  double  chloride.  The  reduction  may  also  be  effected  with 
the  apparatus  described  § 108  (fig.  47,  p.  181),  or  in  a porcelain  boat, 
contained  in  a wide  glass  tube,  instead  of  in  a bulb-tube. 

c.  By  Precipitation  as  Bisulphide  of  Platinum. 

Precipitate  the  solution  with  sulphuretted  hydrogen  water  or  gas,  ac- 
cording to  circumstances,  heat  the  mixture  to  incipient  ebullition,  filter, 
wash  the  precipitate,  dry,  and  ignite  according  to  § 52.  Por  the  prop 
erties  of  the  precipitate  and  residue,  see  § 89.  The  results  are  accurate. 

d.  By  Ignition. 

Heat  in  a covered  porcelain  crucible,  very  gently  at  first,  but  finally 
to  redness,  and  weigh  the  residuary  pure  platinum.  For  the  properties 
of  the  residue,  see  § 89.  The  results  are  most  accurate. 

s.  By  Precipitation  with  Beducing  Agents. 

Various  reducing  agents  may  be  employed  to  precipitate  platinum 
from  its  solutions  in  the  metallic  state.  The  reduction  is  very  promptly 
effected  by  sulphate  of  iron  and  potassa  or  soda  (the  protosesquioxide 
of  iron  being  removed  by  subsequent  addition  of  hydrochloric  acid, 
Hempel),  or  by  pure  zinc  (the  excess  of  which  is  removed  by  hydro- 
chloric acid)  ; somewhat  more  slowly,  and  only  with  application  of  heat, 
by  alkaline  formiates.  Nitrate  of  suboxide  of  mercury  also  precipitates 
the  whole  of  the  platinum  from  solution  of  the  bichloride  ; upon  igniting 
the  brown  precipitate  obtained,  fumes  of  subchloride  of  mercury  escape, 
and  metallic  platinum  remains. 

§125. 

3.  Teroxide  of  Antimony. 

a.  Solution . 

Teroxide  of  antimony,  and  the  compounds  of  that  metal  which  are 
insoluble  in  water,  or  are  decomposed  by  that  agent,  are  dissolved  in 
more  or  less  concentrated  hydrochloric  acid.  Metallic  antimony  is  dis- 
solved best  in  nitrohydrochloric  acid.  The  ebullition  of  a hydrochloric 
acid  solution  of  terchloride  of  antimony  is  attended  with  volatilization 
of  traces  of  the  latter  ; the  concentration  of  a solution  of  the  kind  by 
evaporation  involves  accordingly  loss  of  substance.  Solutions  so  highly 
dilute  as  to  necessitate  a recourse  to  evaporation  must  therefore  pre- 
viously be  supersaturated  with  potassa.  Hydrochloric  acid  solutions 
of  teroxide  of  antimony,  which  it  is  intended  to  dilute  with  water,,  must 
previously  be  mixed  with  tartaric  acid,  to  prevent  the  separation  of  basic 
salt.  In  diluting  an  acid  solution  of  antimonic  acid  in  hydrochloric  acid, 
the  water  must  not  be  added  gradually  and  in  small  quantities  at  a time, 
which  would  make  the  fluid  turbid,  but  in  sufficient  quantity  at  once,, 
which  will  leave  the  fluid  clear. 

b.  Determination. 

Antimony  is  weighed  either  as  tersulphide  or  as  metallic  antimony , or 

16 


DETERMINATION. 


242 


[§  125. 


as  cmtimoniate  of  ter  oxide  (Sb  04)  ; or  it  is  estimated  by  volumetric 
analysis. 

The  oxides  of  antimony,  and  their  salts  with  readily  volatile  or  de- 
composable oxygen  acids,  may  be  converted  into  antimoniate  of  teroxido 
by  simple  ignition.  Antimony  in  solution  is  almost  invariably  first  pre- 
cipitated as  sulphide,  which  is  then,  with  the  view  of  estimation,  con- 
verted into  anhydrous  sulphide,  into  the  metallic  state,  or  into  antimo- 
niate of  teroxide,  or  determined  vol  umetrically.  The  method  of  esti- 
mating antimony  with  a standard  solution  of  iodine  can  only  be  employed 
when  it  is  contained  in  the  solution  as  pure  teroxide.  Hence  it  is  only 
capable  of  limited  application. 


1.  Precipitation  as  Sulphide  of  Antimony. 

Add  to  the  antimony  solution  hydrochloric  acid,  if  not  already  pre- 
sent, then  tartaric  acid,  and  dilute  with  water,  if  necessary.  Introduce 
the  clear  fluid  into  a flask,  closed  with  a doubly  perforated  cork  ; through 
one  of  the  perforations  passes  a tube,  bent  outside  at  a right  angle,  which 
nearly  extends  to  the  bottom  of  the  flask ; through  the  other  perfora- 
tion passes  another  tube,  bent  outside  twice  at  right  angles,  which 
reaches  only  a short  way  into  the  flask ; the  outer  end  of  this  tube  dips 
slightly  under  water.  Conduct  through  the  first  tube  sulphuretted 
hydrogen  gas,  until  it  predominates  strongly ; put  the  flask  in  a mode- 
rately warm  place,  and  after  some  time  conduct  carbonic  acid  into  the 
fluid,  until  the  excess  of  the  other  gas  is  almost  completely  removed ; 
filter  now  without  intermission  through  a weighed  filter,  wash  the  pre- 
cipitate rapidly  and  thoroughly  with  water  mixed  with  a few  drops  of 
sulphuretted  hydrogen  water,  dry  at  100°,  and  weigh.  The  precipitate 
so  weighed  always  retains  some  water,  and  may,  besides,  contain  free 
sulphur  ; in  fact,  it  always  contains  the  latter  in  cases  where  the  anti- 
mony solution,  besides  teroxide  or  terchloride,  contains  antimonic  acid 
or  pentachloride  of  antimony,  since  the  precipitation  under  these  cir- 
cumstances is  preceded  by  a reduction  of  the  higher  oxide  or  chloride 
to  teroxide  or  terchloride,  accompanied  by  separation  of  sulphur.  (H. 
Rose.)  A further  examination  of  the  precipitate  is  accordingly  indis- 
pensable. 

To  this  end,  treat  a sample  of  the  weighed  precipitate  with  strong  hy- 
drochloric acid.  If 

a.  The  sample  dissolves  to  a clear  fluid,  this  is  a proof  that  the  preci- 
pitate only  contains  Sb  S3;  but  if 

b.  Sulphur  separates,  this  shows  that  free  sulphur  is  present. 

In  case  a,  the  greater  portion  of  the  dried  precipitate  is  weighed  in  a 
porcelain  boat,  which  is  then  inserted  into  a sufficiently  wide  glass  tube, 
about  2 decimetres  long ; a slow  current  of  dry  carbonic  acid  is  trans- 
mitted through  the  latter,  and  the  boat  cautiously  heated  by  means  of 
a lamp,  moved  to  and  fro  under  it,  until  the  orange  precipitate  becomes 
black ; this  operation  serves  to  expel  the  whole  of  the  water  present. 
The  precipitate  is  then  allowed  to  cool  in  the  current  of  carbonic  acid, 
and  weighed ; from  the  amount  found,  the  total  quantity  of  anhydrous 
sulphide  of  antimony  contained  in  the  entire  precipitate  is  ascertained 
by  a simple  calculation.  The  results  are  accurate.  Expt.  No.  84  gave 
99*24  instead  of  100.  But  if  the  precipitate  is  simply  dried  at  100°,  the 
results  are  about  2 per  cent,  too  high — see  the  same  experiment.  For 
the  properties  of  the  precipitate,  see  § 90. 

I 


§ 125.] 


TEROXIDE  OF  ANTIMONY. 


243 


In  case  b,  the  precipitate  is  subjected  to  the  same  treatment  as  in  a, 
with  this  difference  only,  that  the  contents  of  the  boat  are  heated  much 
more  intensely,  and  the  process  is  continued  until  no  more  sulphur  is 
expelled.  This  removes  the  whole  of  the  admixed  sulphur  ; the  residue 
consists  of  pure  tersulphide  of  antimony.  It  must  be  completely  solu- 
ble in  fuming  hydrochloric  acid  on  heating. 

According  to  Bunsen  it  is  best  to  convert  the  sulphide  of  antimony 
into  antimoniate  of  teroxide  (see  2), 

The  method  (described  in  § 148)  of  estimating  the  sulphur  in  the  pre- 
cipitate dried  at  100°,  and  calculating  the  antimony  from  the  difference, 
does  not  give  accurate  results,  since  the  precipitate,  besides  antimony 
and  sulphur,  contains  also  water.  In  cases,  therefore,  where  this  indi- 
rect method  is  resorted  to,  the  water  must  first  be  expelled,  as  direct- 
ed in  a. 

The  antimony  may  also  be  determined  in  the  direct  way,  in  the 
precipitate  dried  at  100°.  To  this  end,  an  aliquot  part  of  it  is  weighed 
in  a bulb-tube,  hydrogen  gas  transmitted  through  the  latter,  and  a very 
gentle  heat  applied,  which  is  gradually  increased,  until  no  more  sulphu- 
retted hydrogen  escapes.  It  is  hardly  possible,  however,  to  avoid  a 
slight  loss  of  antimony  in  this  process,  as  a small  portion  of  that  body 
is  but  too  apt  to  be  mechanically  carried  away  by  the  hydrogen  gas. 

For  the  method  of  estimating  the  antimony  in  the  sulphide  volu- 
metrically  and  indirectly,  see  3,  a . 

2.  Determination  as  Antimoniate  of  Teroxide, 

a.  In  the  case  of  teroxide  of  antimony  or  a compound  of  the  same  with 
an  easily  volatile  or  decomposable  oxygen  acid,  evaporate  carefully  with 
nitric  acid,  and  ignite  finally  for  some  time  till  the  weight  is  constant. 
The  experiment  may  be  safely  made  in  a platinum  crucible.  With  anti- 
monic  acid,  the  evaporation  with  nitric  acid  is  unnecessary. 

b.  If  sulphide  of  antimony  is  to  be  converted  into  antimoniate  of  ter- 
oxide, one  of  the  two  following  methods  given  by  Bunsen  * is  employed : — 

a.  Moisten  the  dry  sulphide  of  antimony  with  a few  drops  of  nitric 
acid  of  T42  sp.  gr.,  then  treat,  in  a weighed  porcelain  crucible,  with  con- 
cave lid,  with  8 — 10  times  the  quantity  of  fuming  nitric  acid,]'  and  let 
the  acid  gradually  evaporate  on  the  water-bath.  The  sulphur  separates 
at  first  as  a fine  powder,  which,  however,  is  readily  and  completely  oxidized 
during  the  process  of  evaporation.  The  white  residual  mass  in  the  cruci- 
ble consists  of  antimonic  acid  and  sulphuric  acid,  and  may  by  ignition  be 
converted,  without  loss,  into  antimoniate  of  teroxide  of  antimony.  If  the 
sulphide  of  antimony  contains  a large  excess  of  free  sulphur,  this  must  first 
be  removed  by  washing  with  bisulphide  of  carbon  (see  fi  at  the  end),  before 
proceeding  to  oxidation. 

3.  Mix  the  sulphide  of  antimony  with  30 — 50  times  its  quantity  of 
pure  oxide  of  mercury,];  and  heat  the  mixture  gradually  in  an  open  por- 
celain crucible.  As  soon  as  oxidation  begins,  which  may  be  known  by 
the  sudden  evolution  of  gray  mercurial  fumes,  moderate  the  heat.  When 

^ 

* Annal.  d.  Chem.  u.  Pharm.  106,  3. 

f Nitric  acid  of  1 ‘42  sp.  gr.  is  not  suitable  for  this  purpose,  as  its  boiling  point 
is  almost  10 J above  the  fusing  point  of  sulphur,  whereas  fuming  nitric  acid  boils 
at  86°,  consequently  below  the  fusing  point  of  sulphur.  With  nitric  acid  of  1*42 
sp.  gr. , therefore,  the  separated  sulphur  fuses  and  forms  drops,  which  obstinately 
resist  oxidation. 

X It  is  best  to  use  that  prepared  in  the  wet  way. 


244 


DETERMINATION. 


L§  125. 

the  evolution  of  mercurial  fumes  diminishes  raise  the  temperature  again, 
always  taking  care,  however,  that  no  reducing  gases  come  in  contact  with 
the  contents  of  the  crucible.  Remove  the  last  traces  of  oxide  of  mercury 
over  the  blast  gas-lamp,  then  weigh  the  residual  fine  white  powder  of 
antimoniate  of  teroxide  of  antimony.  As  oxide  of  mercury  generally  leaves 
a trifling  fixed  residue  upon  ignition,  the  amount  of  this  should  be  deter- 
mined once  for  all,  the  oxide  of  mercury  added  approximately  weighed, 
and  the  corresponding  amount  of  fixed  residue  deducted  from  the  antimo- 
niate of  teroxide  of  antimony.  The  volatilization  of  the  oxide  of  mercury 
proceeds  much  more  rapidly  when  effected  in  a platinum  crucible,  instead 
of  a porcelain  one.  But,  if  a platinum  crucible  is  employed,  it  must  be 
effectively  protected  from  the  action  of  antimony  upon  it,  by  a good  lining 
of  oxide  of  mercury.*  If  the  sulphide  of  antimony  contains  free  sulphur, 
this  must  first  be  removed  by  washing  with  bisulphide  of  carbon,  before 
the  oxidation  can  be  proceeded  with,  since  otherwise  a slight  deflagration 
is  unavoidable.  The  bisulphide  of  carbon  used  may  be  very  easily  rec- 
tified, and  then  used  again,  so  that  the  washing  of  a precipitate  may  be 
effected  with  as  little  as  10 — 15  grammes  of  bisulphide  of  carbon. 

3.  Volumetric  Methods. 

The  proposals  under  this  head  are  based,  either, 

a.  Upon  the  decomposition  of  the  sulphide  on  boiling  with  hydrochloric 
acid,  and  the  determination  of  the  sulphuretted  hydrogen  evol  ved.  (R. 
Schneider,  j*) 

h.  Upon  the  oxidation  of  the  teroxide  with  permanganate  (Kessler  J). 

a.  Volumetric  Estimation  by  determining  the  Sulphuretted,  Hydrogen 
given  up  by  the  Sulphide. 

Both  tersulphide  and  pentasulphide  yield  under  the  action  of  boiling 
hydrochloric  acid  3 eq.  of  sulphuretted  hydrogen  for  every  1 eq.  of  anti- 
mony. Hence,  if  the  amount  of  the  gas  evolved  under  such  circumstances 
is  estimated,  the  amount  of  antimony  is  known. 

For  decomposing  the  sulphide  and  absorbing  the  gas  the  same  apparatus 
serves  as  Bunsen  employs  for  his  iodimetric  analyses  (§  130,  fig.  51). 
The  size  of  the  boiling  flask  should  depend  on  the  quantity  of  sulphide  : 
for  quantities  up  to  0*4  grm.  Sb  S3,  a flask  of  100  c.  c.  is  large  enough ; 
for  *4 — 1‘0  grm.,  use  a 200  c.  c.  flask.  The  body  of  the  flask  should  be 
spherical,  the  neck  rather  narrow,  long,  and  cylindrical.  If  the  sulphide 
of  antimony  is  on  a filter,  put  both  together  into  the  flask.  The  hydro- 
chloric acid  should  not  be  too  concentrated. 

The  determination  of  the  sulphuretted  hydrogen  is  best  conducted 


* This  is  effected  best,  according-  to  Bunsen,  in  the  following-  way  : Soften  the 
sealed  end  of  a common  test-  tube  before  the  glass-blower’s  lamp  ; place  the  sof- 
tened end  in  the  centre  of  the  platinum  crucible,  and  blow  into  it,  which  will 
cause  it  to  expand  and  assume  the  exact  form  of  the  interior  of  the  crucible. 
Crack  off  the  bottom  of  the  little  flask  so  formed,  and  smooth  the  sharp  edge 
cautiously  by  fusion.  A glass  is  thus  obtained,  open  at  both  ends,  which  exactly 
fits  the  crucible.  To  effect  the  lining  by  means  of  this  instrument,  fill  the  crucible 
loosely  with  oxide  of  mercury  up  to  the  brim,  then  force  the  glass  gradually  and 
slowly  down  to  the  bottom  of  the  crucible,  occasionally  shaking  out  the  oxide  of 
mercury  from  the  interior  of  the  glass.  The  inside  of  the  crucible  is  thus  covered 
with  a layer  of  oxide  of  mercury  £—1  line  thick,  which,  after  the  removal  of  the 
glass,  adheres  with  sufficient  firmness,  even  upon  ignition. 

f Pogg.  Anna!.  110,  634.  % Zeitschrift  f.  anal.  Chem.  2,  383. 


126.] 


PROTOXIDE  AND  BINOXIDE  OF  TIN. 


245 


according  to  the  method  given  in  § 148,  b.  The  results  obtained  by 
Schneider  are  satisfactory. 

If  the  precipitate  contains  chloride  of  antimony,  the  results  are  of  course 
false,  and  this  would  actually  be  the  case  if  on  precipitation  with  sulphu- 
retted hydrogen  the  addition  of  tartaric  acid  were  omitted. 

b.  Volumetric  Determination  with  Permanganate  of  Potash. 

In  the  absence  of  organic  matter,  heavy  metallic  oxides,  and  other 
bodies  which  are  detrimental  to  the  reaction,  dissolve  the  substance  con- 
taining teroxide  of  antimony,  at  once  in  hydrochloric  acid.  The  solution 
should  contain  not  less  than  £ of  its  volume  of  hydrochloric  acid  of  1 T 2 
sp.  gr. 

The  permanganate  solution,  which  may  contain  about  T5  grm.  of  the 
crystallized  salt  in  a litre,  is  added  to  permanent  reddening.  The  end- 
reaction  is  exact,  and  the  oxidation  of  the  teroxide  of  antimony  to  anti- 
monic  acid  goes  on  uniformly,  although  the  degree  of  dilution  may  vary, 
provided  the  above  relation  between  hydrochloric  acid  and  water  is  kept 
up.  It  is  not  well  that  the  hydrochloric  acid  should  exceed  of  the  volume 
of  the  fluid,  as  in  that  case  the  end-reaction  would  be  too  transitory. 
Tartaric  acid,  at  least  in  the  proportion  to  teroxide  of  antimony  in  which 
it  exists  in  tartar  emetic,  does  not  interfere  with  the  reaction.  Hence 
the  permanganate  may  be  standardized  by  the  aid  of  solution  of  tartar 
emetic  of  known  strength. 

If  the  direct  determination  of  the  hydrochloric  acid  solution  is 
not  practicable,  precipitate  it  with  sulphuretted  hydrogen.  Wash  the 
precipitate,  transfer  it,  together  with  the  filter,  to  a small  flask  ; treat 
it  with  a sufficiency  of  hydrochloric  acid,  dissolve  by  digestion  on  the 
water-bath,  add  a sufficient  quantity  of  a nearly  saturated  solution  of 
chloride  of  mercury  in  hydrochloric  acid  of  1*12  sp.  gr.  to  remove  the 
sulphuretted  hydrogen,  make  the  fluid  up  to  a certain  volume,  allow 
to  settle,  and  use  a measured  portion  of  the  perfectly  clear  solution  for 
the  experiment. 

§ 126. 

4.  Protoxide  of  Tin,  and  5.  Binoxide  of  Tin. 

a.  Solution. 

In  dissolving  compounds  of  tin  soluble  in  water,  a little  hydrochloric 
acid  is  added  to  insure  a clear  solution.  Nearly  all  the  compounds  of 
tin  insoluble  in  water  dissolve  in  hydrochloric  acid  or  in  aqua  regia. 
The  hydrate  of  metastannic  acid  may  be  dissolved  by  boiling  with  hydro- 
chloric acid,  decanting  the  fluid,  and  treating  the  residue  with  a large 
proportion  of  water.  Ignited  binoxide  of  tin,  and  compounds  of  the 
binoxide  insoluble  in  acids,  are  prepared  for  solution  in  hydrochloric 
acid,  by  reducing  them  to  the  state  of  a fine  powder,  and  fusing  in  a sil- 
ver crucible  with  hydrate  of  potassa,  or  soda,  in  excess.  Metallic  tin  is 
dissolved  best  in  aqua  regia ; it  is  generally  determined,  however,  by 
converting  it  into  binoxide,  without  previous  solution.  Acid  solutions 
of  binoxide  of  tin,  which  contain  hydrochloric  acid,  or  a chloride,  can- 
not be  concentrated  by  evaporation,  not  even  after  the  addition  of  nitric 
acid  or  sulphuric  acid,  without  volatilization  of  bichloride  of  tin  taking 
place. 


246 


DETERMINATION-. 


[§  126. 


b.  Determination. 

Tin  is  weighed  in  the  form  of  binoxide , into  which  it  is  converted, 
either  by  the  agency  of  nitric  acid,  or  by  precipitation  as  hydrated 
binoxide,  or  by  precipitation  as  sulphide. 

A great  many  volumetric  methods  of  estimating  tin  have  been  pro- 
posed. They  all  depend  on  obtaining  the  tin  in  solution  in  the  con- 
dition of  protochloride,  and  converting  this  into  bichloride  either  in  alkar 
line  or  acid  solution.  A few  only  yield  satisfactory  results. 

We  may  convert  into 

Binoxide  of  Tin. 

a.  Dy  the  agency  of  Nitric  Acid. 

Metallic  tin,  and  those  compounds  of  tin  which  contain  no  fixed  acid, 
provided  no  compounds  of  chlorine  be  present. 

b.  By  Precipitation  as  Hydrated  Bin/oxide. 

All  compounds  of  tin  containing  volatile  acids,  provided  no  non-vola- 
tile organic  substances  nor  sesquioxide  of  iron  be  present. 

c.  By  Precipitation  as  Sulphide. 

All  compounds  of  tin  without  exception. 

In  methods  a and  c,  it  is  quite  indifferent  whether  the  tin  is  present 
in  the  state  of  protoxide  or  in  that  of  binoxide.  The  method  b requires 
the  tin  to  be  present  in  the  state  of  binoxide.  The  volumetric  methods 
may  be  employed  in  all  cases ; but  the  estimation  is  simple  and  direct 
only  where  the  tin  is  in  solution  as  protochloride  and  free  from  other 
oxidizable  bodies,  or  can  readily  be  brought  into  this  state.  For  the 
methods  of  determining  the  protoxide  and  binoxide  in  presence  of  each 
other,  I refer  to  Section  V. 

1.  Determination  of  Tin  as  Binoxide. 

a.  By  Treating  with  Nitric  Acid. 

This  method  is  resorted  to  principally  to  convert  the  metallic  tin  into 
binoxide.  For  this  purpose  the  finely-divided  metal  is  put  into  a capa- 
cious flask,  and  moderately  concentrated  pure  nitric  acid  (about  T3  sp. 
gr.)  gradually  poured  over  it ; the  flask  is  covered  with  a watch-glass. 
When  the  first  tumultuous  action  of  the  acid  has  somewhat  abated,  a 
gentle  heat  is  applied  until  the  binoxide  formed  appears  of  a pure  white 
color,  and  further  action  of  the  acid  is  no  longer  perceptible.  The  contents 
of  the  flask  are  then  transferred  to  a porcelain  dish  and  evaporated  on  a 
water-bath  to  dryness,  water  is  then  added,  and  the  precipitate  is  collected 
on  a filter,  washed,  till  the  washings  scarcely  redden  litmus  paper,  dried, 
ignited,  and  weighed.  . The  ignition  is  effected  best  in  a small  porcelain 
crucible,  according  to  the  directions  given  in  § 53  ; still  a platinum  cru- 
cible may  also  be  used.  A simple  red  heat  is  not  sufficient  to  drive  oft' 
all  the  wTater ; the  ignition  must  therefore  be  finished  over  a gas  blast- 
lamp.  Compounds  of  tin  which  contain  no  fixed  substances  may  be  con- 
verted into  binoxide  by  treating  them  in  a porcelain  crucible  with  nitric 
acid,  evaporating  to  dryness,  and  igniting  the  residue.  If  sulphuric  acid 
be  present,  the  expulsion  of  that  acid  maybe  promoted,  in  the  last  stages 
of  the  process,  by  carbonate  of  ammonia,  as  in  the  case  of  bisulphate  of 
potassa  (§  97) ; here  also  the  heat  must  be  increased  as  much  as  possi- 


§ 126-1 


PROTOXIDE  AND  BINOXIDE  OF  TIN. 


247 


ble  at  tlie  end.  For  the  properties  of  the  residue,  see  § 91.  The  results 
are  accurate. 

b.  By  Precipitation  as  Hydrate  of  Pinoxide. 

The  application  of  this  method  presupposes  the  whole  of  the  tin  to  be 
present  in  the  state  of  binoxide  or  bichloride.  Therefore,  if  a solution 
contains  protoxide,  either  mix  with  chlorine  water,  or  conduct  chlorine 
gas  into  it,  or  heat  gently  with  chlorate  of  potassa,  until  the  conversion 
of  the  protoxide  into  binoxide  is  effected.  When  this  has  been  done, 
add  ammonia  until  a permanent  precipitate  just  begins  to  form,  and 
then  hydrochloric  acid,  drop  by  drop,  until  this  precipitate  is  completely 
redissolved ; by  this  means  a large  excess  of  hydrochloric  acid  in  the 
solution  will  be  avoided.  Add  to  the  fluid  so  prepared  a concen- 
trated solution  of  nitrate  of  ammonia  (or  sulphate  of  soda),  and  apply 
heat  for  some  time,  whereupon  the  whole  of  the  tin  will  precipitate  as 
hydrate  of  binoxide.  Decant  three  times  on  to  a filter,  then  collect  the 
precipitate  on  the  latter,  wash  thoroughly,  dry,  and  ignite.  To  make 
quite  sure  that  the  whole  of  the  tin  has  separated,  you  need  simply,  be- 
fore proceeding  to  filter,  add  a few  drops  of  the  clear  supernatant  fluid 
to  a hot  solution  of  nitrate  of  ammonia,  or  sulphate  of  soda,  when  the 
formation  or  nonformation  of  a precipitate  will  at  once  decide  the  ques- 
tion. 

This  method,  which  we  owe  to  J.  Lowenthal,  has  been  repeatedly 
tested  by  him  in  my  own  laboratory,*  is  easy  and  convenient,  and  gives 
very  accurate  results.  The  decomposition  is  expressed  by  the  equation, 
SnCl2  + 2 (NH4  0,N06)  f 2 HO  = Sn  02-{-2  NH4  Cl  + 2 (N08,H0),  or, in 
precipitating  with  sulphate  of  soda:  Sn  Cl2+4  (Na  O,  S 03)fl-2  H 0= 
Sn  03  + 2 Na  Cl  + 2 (Na  O,  H O,  2 S 03).  - 

Tin  may  also,  according  to  H.  Rose,  -j-  be  completely  precipitated  from 
solutions  of  the  binoxide  or  bichloride,  by  sulphuric  acid.  If  the  solu- 
tion contains  metastannic  acid  or  metachloride  of  tin,  the  precipitation 
is  effected  without  extraordinary  dilution  ; on  the  contrary,  if  it  contains 
the  other  modification  of  the  binoxide  or  bichloride,  very  considerable 
dilution  is  necessary.  If  free  hydrochloric  acid  is  absent,  the  precipita- 
tion is  rapid;  in  other  cases  12  or  24  hours  at  least  are  required  for 
perfect  precipitation.  Allow  to  settle  thoroughly,  before  filtering,  wash 
well  (if  hydrochloric  acid  was  present,  till  the  washings  give  no  turbid- 
ity with  nitrate  of  silver),  dry  and  ignite,  at  last  intensely  with  addition 
of  some  carbonate  of  ammonia.  The  results  obtained  by  Oesten,  and 
communicated  by  H.  Rose,  are  exact. 

c.  By  Precipitation  as  Protosulphide  or  Bisulphide  of  Tin. 

Precipitate  the  dilute  moderately  acid  solution  with  sulphuretted  hy- 
drogen water  or  gas.  If  the  tin  was  present  in  the  solution  in  the  form 
of  protoxide,  and  the  precipitate  consists  accordingly  of  the  brown  pro- 
tosulphide, keep  the  solution,  supersaturated  with  sulphuretted  hydro- 
gen, standing  for  half  an  hour  in  a moderately  warm  place,  and  then 
filter ; if,  on  the  other  hand,  the  solution  contain  a salt  of  binoxide  of 
tin,  and  the  precipitate  consists  accordingly  of  the  yellow  bisulphide, 
put  the  fluid,  loosely  covered,  in  a warm  place,  until  the  odor  of  sul- 
phuretted hydrogen  has  nearly  gone  off,  and  then  filter.  The  washing 


* Journ.  f.  prakt.  Chem.  56,  366. 


f Po gg.  Anna!.  112,  164. 


248 


DETERMINATION. 


[§  126. 


of  the  bisulphide  of  tin  precipitate  which  has  a great  inclination  to  pass 
through  the  filter,  is  best  effected  with  a concentrated  solution  of  chlo- 
ride of  sodium,  the  remains  of  the  latter  being  got  rid  of  by  a solution 
of  acetate  of  ammonia  containing  a small  excess  of  acetic  acid.  If  there 
is  no  objection  to  having  the  latter  salt  in  the  filtrate,  the  washing  may 
be  entirely  effected  by  its  means  (Bunsen* * * §).  Put  the  filter,  with  the 
not  yet  quite  dry  precipitate  on  it,  into  a porcelain  crucible,  and  apply 
a very  gentle  heat,  with  free  access  of  air,  until  the  odor  of  sulphurous 
acid  is  no  longer  perceptible.  Increase  the  heat  now  gradually  to  a high 
degree  of  intensity,  and  treat  the  residue  repeatedly  with  some  carbonate 
of  ammonia  (see  «■),  in  order  to  insure  the  complete  expulsion  of  the 
sulphuric  acid  which  maybe  present.  Were  you  to  apply  a very  intense 
heat  from  the  beginning,  fumes  of  bisulphide  of  tin  would  escape,  which 
burn  to  binoxide  (H.  Bose).  For  the  properties  of  the  precipitates,  see 
§91.  The  results  are  accurate. 

2.  Volumetric  Methods. 

The  determination  of  tin  by  the  conversion  of  the  proto-  into  bichlo- 
ride with  the  aid  of  oxidizing  agents  (bichromate  of  potassa,  iodine,  per- 
manganate of  potassa,  &c.)  offers  peculiar  difficulties,  inasmuch  as  on  the 
one  hand  the  protochloride  of  tin  takes  up  oxygen  from  the  air  and  from 
the  water  used  for  dilution,  with  more  or  less  rapidity,  according  to  cir- 
cumstances ; and  on  the  other  hand,  the  energy  of  the  oxidizing  agent  is 
not  always  the  same,  being  influenced  by  the  state  of  dilution  and  the 
presence  of  a larger  or  smaller  excess  of  acid. 

In  the  following  methods,  these  sources  of  error  are  avoided  or  limited 
in  such  a manner  as  to  render  the  results  satisfactory. 

1.  Estimation  of  Protochloride  of  Tin  by  Iodine  in  Alkaline 
Solution  ( after  Lenssen  f). 

Dissolve  the  protosalt  of  tin  or  the  metallic  tin  J in  hydrochloric  acid 
(preferably  in  a stream  of  carbonic  acid),  add  Bochelle  salt,  then  bicar- 
bonate of  soda  in  excess.  To  the  clear  alkaline  solution  thus  formed 
add  some  starch-solution,  and  afterwards  the  iodine  solution  of  § 146, 
till  a permanent  blue  coloration  appears.  1 eq.  free  iodine  used  cor- 
responds to  1 eq.  tin. 

Lenssen’s  results  are  entirely  satisfactory. 

2.  Estimation  of  the  Protochloride  of  Tin , after  addition  of 
Sesquichloride  of  Iron. 

Protochloride  of  tin  in  acid  solution  is  best  oxidized  by  oxidizing 
agents  after  being  mixed  with  sesquichloride  of  iron  (Lowenthal,  § 
Stromeyeii  I). 

a.  The  given  substance  is  a proto-salt  of  tin.  Dissolve  in  pure  ses- 


* Anna!  d.  Chem.  u.  Pharm.  106,  13. 

f Joum.  f.  prakt.  Chem.  78,  200;  Anna!  d.  Chem.  u.  Pharm.  114,  113. 

x The  solution  of  metallic  tin  is  much  assisted  by  the  presence  of  platinum 
foil,  which  is  accordingly  added.  Lenssen  found  this  addition  of  platinum  to  be 
objectionable  ; but  no  other  experimenter  has  observed  that  it  interferes  with 
the  accuracy  of  the  results. 

§ Journ.  f.  prakt.  Chem.  76,  484.  1 Anna!,  d.  Chem.  u.  Pharm.  117,  261. 


§ 127.] 


ARSENIOUS  AND  ARSENIC  ACIDS. 


249 


quichlori.de  of  iron  (free  from  protochloride)  with  addition  of  hydro- 
chloric acid,  dilute  and  add  standard  permanganate  from  the  burette. 
Now  make  another  experiment  with  the  same  quantity  of  water  similarly 
colored  with  sesquichloride  of  iron  to  ascertain  how  much  permanganate 
is  required  to  tinge  the  liquid,  and  subtract  the  quantity  so  used  from 
the  amount  employed  in  the  actual  analysis,  and  from  the  remainder 
calculate  the  tin. 

The  reaction  between  the  tin  salt  and  the  iron  solution  is  SnCl  -f- 
Fe2Cl3  = SnCl2  + 2 Fe  Cl.  The  solution  thus  contains  protochloride  of 
iron  in  the  place  of  proto-salt  of  tin,  the  former  being,  as  is  well  known, 
far  less  susceptible  of  alteration  from  the  action  of  free  oxygen  than  the 
latter.  2 eq.  iron  found  correspond  to  1 eq.  tin. 

b.  The  given  substance  is  metallic  tin.  Either  dissolve  in  hydro- 
chloric acid — preferably  with  addition  of  platinum  and  in  an  atmosphere 
of  carbonic  acid — and  treat  the  solution  according  to  a,  or  place  the 
substance  at  once  in  a concentrated  solution  of  sesquichloride  of  iron, 
mixed  with  a little  hydrochloric  acid  ; under  these  circumstances  it  will, 
if  finely  divided,  dissolve  quickly  even  in  the  cold  and  without  evolu- 
tion of  hydrogen.  Gentle  warming  is  unobjectionable.  Now  add  the 
permanganate.  The  reaction  is  Sn  + 2 Fe2Cl3=Sn  Cl2  + 4 Fe  Cl, 
therefore  every  4 eq.  iron  found  reduced  correspond  to  1 eq.  tin. 
The  results  are  of  course  only  correct  when  iron  is  not  present. 
Where  this  is  the  case,  proceed  with  the  impure  tin  solution  accord- 
ing to  c. 

c.  The  given  substance  is  bichloride  of  tin,  or  binoxide  of  tin,  or  a 
compound  of  tin  containing  iron.  Dissolve  in  water  with  addition  of 
hydrochloric  acid,  place  a plate  of  zinc  in  the  solution  and  allow  to  stand 
twelve  hours,  then  remove  the  precipitated  tin  with  a brush,  wash  it, 
dissolve  in  sesquichloride  of  iron,  and  proceed  as  in  b. 

d.  The  given  substance  is  pure  bisulphide  of  tin,  precipitated  out  of 
an  acid  solution  of  binoxide  free  from  protoxide.  Mix  with  sesqui- 
chloride of  iron,  heat  gently,  filter  oft*  the  sulphur,  and  then  add  the 
permanganate.  4 eq.  iron  correspond  to  1 eq.  tin,  for  SnS2  + 2 Fe2Cl3  = 
SnCl2  + 4 FeCl  + 2 S.  The  results  obtained  by  Stromeyer  are  quite 
satisfactory. 


§ 127. 

6.  Arsenious  Acid,  and  7.  Arsenic  Acid. 

a.  Solution. 

The  compounds  of  arsenious  and  arsenic  acids  which  are  not  soluble  in 
water  are  dissolved  in  hydrochloric  acid  or  in  nitrohydrochloric  acid. 
Some  native  arseniates  require  fusing  with  carbonate  of  soda.  Metallic 
arsenic,  sulphide  of  arsenic  and  metallic  arsenides  are  dissolved  in  fuming 
nitric  acid  or  nitrohydrochloric  acid  ; those  metallic  arsenides  which  are 
insoluble  in  these  menstrua  are  fused  with  carbonate  of  soda  and  nitrate 
of  potassa,  by  which  means  they  are  converted  into  soluble  arseniates  of 
the  alkalies  and  insoluble  metallic  oxides,  or  they  may  be  suspended  in 
potassa  solution  and  treated  with  chlorine  (§164,  B,  7).  In  this  last 
manner  too,  sulphide  of  arsenic,  dissolved  in  concentrated  potassa,  may 
be  very  easily  rendered  soluble.  All  solutions  of  compounds  of  arsenic 
which  have  been  effected  by  long  heating  with  fuming  nitric  acid,  or  by 


250 


DETERMINATION. 


[§  127. 

warming  with  excess  of  nitrohydrochloric  acid,  or  chlorine,  contain 
arsenic  acid.  A solution  of  arsenious  acid  in  hydrochloric  acid  cannot 
be  concentrated  by  evaporation,  since  chloride  of  arsenic  would  escape 
with  the  hyd/ochloric  acid  fumes.  This,  however,  less  readily  takes 
place  if  the  solution  contains  arsenic  acid  ; it  is  advisable  in  all  cases 
where  a hydrochloric  acid  solution  containing  arsenic  is  to  be  concen- 
trated, previously  to  render  the  same  alkaline. 

b.  Determination. 

A rsenic  is  weighed  as  arseniate  of  lead,  or  as  arseniate  of  magnesia 
and  ammonia , or  as  arseniate  of  sesquioxide  of  iron , or  as  tersulpliide  of 
arsenic.  The  determination  as  arseniate  of  magnesia  and  ammonia  is 
sometimes  preceded  by  precipitation  as  arsenio-molybdate  of  ammonia. 
Arsenic  may  be  estimated  also  in  an  indirect  way,  and  by  volumetric  methods. 

We  may  convert  into 

1.  Arseniate  of  Lead. 

Arsenious  and  arsenic  acids  in  aqueous  or  nitric  acid  solution.  (Acids 
or  halogens  forming  fixed  salts  with  oxide  of  lead  or  metallic  lead,  must 
not  be  present.) 

2.  Arseniate  of  Magnesia  and  Ammonia. 

a.  Dy  Direct  Precipitation. 

Arsenic  acid  in  all  solutions  free  from  bases  or  acids  precipitable  by 
magnesia  or  ammonia. 

b.  Preceded  by  Precipitation  as  Arsenio-Molybdate  of  Ammonia. 

Arsenic  acid  in  all  cases  where  no  phosphoric  acid  is  present,  nor  any 

substance  by  which  molybdic  acid  is  decomposed. 

3.  Arseniate  of  Sesquioxide  of  Iron. 

Arsenic  acid  in  solutions  free  from  substances  precipitable  by  sesqui- 
chloride  of  iron  with  addition  of  ammonia  or  carbonate  of  baryta. 

4.  Tersulphide  of  Arsenic. 

All  compounds  of  arsenic  without  exception. 

Arsenic  may  be  determined  volumetrically  in  a simple  and  exact  man- 
ner, whether  present  in  the  form  of  arsenious  acid  or  an  alkaline  arsenite, 
or  as  arsenic  acid  or  an  alkaline  arseniate.  The  volumetric  methods  have 
now  almost  entirely  superseded  the  indirect  gravimetric  methods  formerly 
employed  to  effect  the  estimation  of  arsenious  acid. 

1.  Determination  as  Arseniate  of  Lead. 

a.  Arsenic  Acid  in  Aqueous  Solution. 

A weighed  portion  of  the  solution  is.  put  into  a platinum  or  porcelain 
dish,  and  a weighed  amount  of  recently  ignited  pure  oxide  of  lead  added 
(about  five  or  six  times  the  supposed  quantity  of  arsenic  acid  present)  ; 
the  mixture  is  cautiously  evaporated  to  dryness,  and  the  residue  heated 
to  gentle  redness,  and  maintained  some  time  at  this  temperature.  The 
residue  is  arseniate  of  lead -{-oxide  of  lead.  The  quantity  of  arsenic  acid 
is  now  readily  found  by  subtracting  from  the  weight  of  the  residue  that 
of  the  oxide  of  lead  added. 


ARSENIOUS  AND  ARSENIC  ACIDS. 


251 


§ 127.] 

For  the  properties  of  arseniate  of  lead,  see  § 92.  The  results  are  per- 
fectly accurate,  provided  the  residue  he  not  heated  beyond  gentle  redness. 

b.  Arsenious  Acid  in  Solution. 

Mix  the  solution  with  nitric  acid,  evaporate  to  a small  bulk,  add  a 
weighed  quantity  of  oxide  of  lead  in  excess,  evaporate  to  dryness,  and 
ignite  the  residue  most  cautiously  in  a covered  crucible,  until  the  whole 
of  the  nitrate  of  lead  is  decomposed.  The  residue  consists  here  also  of 
arsenic  acid  + oxide  of  lead.  This  method  requires  considerable  care  to 
guard  against  loss  by  decrepitation  upon  ignition  of  the  nitrate  of  lead. 

2.  Estimation  as  Arseniate  of  Magnesia  and  Ammonia . 

a.  By  Direct  Precipitation. 

This  method,  which  was  first  recommended  by  Levol,  presupposes 
that  the  whole  of  the  arsenic  is  contained  in  the  solution  in  the  form  of 
arsenic  acid.  Where  this  is  not  the  case,  the  solution  is  gently  heated, 
in  a capacious  flask,  with  hydrochloric  acid,  and  chlorate  of  potassa  added 
in  small  portions,  until  the  fluid  emits  a strong  smell  of  chlorous  acid ; it 
is  then  allowed  to  stand  at  a gentle  heat  until  the  odor  of  this  gas  is  nearly 
gone  off. 

The  arsenic  acid  solution  is  now  mixed  with  ammonia  in  excess,  which 
must  not  produce  turbidity,  even  after  standing  some  time ; a solution 
of  sulphate  of  magnesia  is  then  added,  containing  chloride  of  ammonium 
in  sufficient  quantity  to  prevent  its  being  rendered  turbid  by  ammonia. 
(The  best  way  is  to  keep  a solution  of  sulphate  of  magnesia  mixed  with 
chloride  of  ammonium  and  ammonia  ready  prepared  in  the  laboratory — 
see  § 62,  6.)  The  fluid,  which  smells  strongly  of  ammonia,  is  allowed  to 
stand  12  hours  in  the  cold,  and  then  filtered  through  a weighed  filter. 
The  precipitate  is  then  transferred  to  the  filter,  with  the  aid  of  portions 
of  the  filtrate  so  as  to  use  no  more  washing  water  than  necessary,  and 
washed  with  small  quantities  of  a mixture  of  three  parts  water  and 
one  part  ammonia,  till  the  washings  on  being  mixed  with  nitric  acid 
and  nitrate  of  silver  show  only  a slight  opalescence.  The  precipitate  is 
dried  at  105  to  110°,  and  weighed.  It  has  the  formula,  2 Mg  O,  N II4 
O,  As  05-}-aq.* 

For  its  properties,  see  § 92.  This  process  yields,  it  is  true,  satisfac- 
tory results,  but  they  are  still  always  somewhat  too  low,  as  the  precipi- 
tate is  perceptibly  soluble  even  in  ammoniacal  water.  The  error  may 
be  diminished  by  measuring  the  filtrate  (without  the  washings)  and  add- 
ing for  every  16  c.  c.  1 mgrm.  to  the  weight  found  of  the  precipitate. 
To  extend  the  correction  to  the  washings  is  inadmissible,  since  they 
cannot  be  regarded  as  a saturated  solution. 

b.  Preceded  by  Precipitation  as  Arsenio-Molybdate  of  Ammonia. 

Mix  the  acid  solution,  which  must  be  free  from  phosphoric  and  silicic 

acids,  with  an  excess  of  solution  of  molybdate  of  ammonia.  The  molyb- 
date of  ammonia  solution  should  have  been  previously  mixed  with 
nitric  acid  in  excess,  and  the  whole  process  is  conducted  exactly  as  in  the 
case  of  phosphoric  acid — see  § 134,  5,  j3.  Treat  the  arseniate  of  mag- 
nesia and  ammonia  thrown  down  from  the  ammoniacal  solution  of  the 


* If  it  is  dried  in  a water-bath,  the  drying  must  be  extremely  prolonged,  or  other- 
wise more  than  1 aq.  will  be  left.  After  brief  drying  in  the  water-bath  the  com- 
pound contains  between  1 and  3 eq.  water. 


DETERMINATION. 


252 


[§  127. 


arsenio-molybdate  of  ammonia  with  a mixture  of  sulphate  of  magnesia 
and  chloride  of  ammonium,  as  in  a.  Results  satisfactory. 

3.  Estimation  as  Arseniate  of  Sesquioxide  of  Iron . 

(Berthier  and  v.  Ko  bell’s  method.) 

a.  The  Solution  contains  no  other  fixed  Eases  besides  Alkalies. 

Add  to  the  solution  a measured  quantity  of  solution  of  sesquioxide  of 
iron  of  known  strength,  and  precipitate  with  ammonia.  (The  preci- 
pitate must  be  reddish  brown  : if  not  of  that  color,  it  is  a sign  that  a 
sufficient  quantity  of  the  solution  of  sesquioxide  of  iron  has  not  been 
added.)  Allow  to  stand  some  time  at  a gentle  heat ; filter,  wash,  and 
dry  the  precipitate ; then  expose  first  to  a very  gentle  heat,  to  insure 
the  expulsion  of  the  ammonia  at  a temperature  at  which  it  cannot  exer- 
cise a reducing  action  upon  the  arsenic  acid  ; after  a time,  increase  the 
heat  gradually,  at  last  subjecting  the  residue  to  intense  ignition,  till  the 
weight  remains  constant.  The  residue  is  basic  arseniate  of  sesquioxide 
of  iron  -(-  sesquioxide  of  iron,  or  in  other  words,  sesquioxide  of  iron 
arsenic  acid.  Deduct  from  the  weight  of  the  residue  the  weight  of  the 
sesquioxide  of  iron  added : the  difference  expresses  the  quantity  of 
arsenic  acid  contained  in  the  analyzed  solution.  A solution  of  sesqui- 
oxide of  iron  of  known  strength  for  the  above  purpose  is  best  prepared 
by  dissolving  fine  iron  wire  in  nitric  acid  by  the  aid  of  heat,  diluting 
suitably,  and  determining  the  sesquioxide  of  iron  in  10  c.  c.  by  precipi- 
tation with  ammonia  (see  § 113,  1,  a ).  The  presence  of  a small  amount 
of  silicic  acid  in  the  solution  of  sesquioxide  of  iron  is  then  without 
injurious  influence,  since  the  same  is  weighed  with  the  iron  both 
in  the  determination  of  the  strength  of  the  solution  and  in  the  arsenic- 
estimation. 

b.  The  Solution  contains  other  fixed  Eases  besides  Alkalies. 

The  preceding  method  of  Berthier  is  modified  by  v.  Kobell  as  fol- 
lows, provided  the  bases  present  in  the  solution  are  not  precipitated  by 
carbonate  of  baryta  in  the  cold.  The  solution  is  mixed  with  solution  of 
sesquioxide  of  iron  of  known  strength,  as  in  a,  but  instead  of  ammonia, 
carbonate  of  baryta  is  added  in  excess  (should  the  fluid  contain  a large 
excess  of  free  acid,  it  is  advisable  to  nearly  neutralize  this  previously 
with  carbonate  of  soda;  the  fluid  must,  however,  still  remain  clear). 
The  mixture  is  then  allowed  to  stand  several  hours  in  the  cold,  and  the 
precipitate,  which  contains  the  whole  of  the  sesquioxide  of  iron,  the 
whole  of  the  arsenic  acid,  and  the  excess  of  carbonate  of  baryta,  is  washed 
with  cold  water,  first  by  decantation,  then  upon  the  filter,  dried,  gently 
ignited  for  some  time , and  weighed.  The  residue  is  dissolved  in  hydro- 
chloric acid,  the  amount  of  baryta  contained  in  it  determined  by  means 
of  sulphuric  acid,  the  sulphate  of  baryta  obtained  calculated  to  car- 
bonate, and  the  calculated  weight,  together  with  the  known  weight  of 
the  sesquioxide  of  iron,  subtracted  from  the  weight  of  the  original  resi- 
due : the  difference  expresses  the  quantity  of  arsenic  acid  contained  in 
the  analyzed  solution.  This  method  presupposes  the  absence  of  sulphuric 
acid.  In  cases,  therefore,  where  that  acid  is  present,  it  must  be  removed 
before  the  carbonate  of  baryta  can  be  added  ; which  is  effected  by  preci- 
pitating with  chloride  of  barium,  and  filtering  off  the  precipitate. 


§ 127.] 


ARSENIOUS  AND  ARSENIC  ACIDS. 


253 


4.  Determination  as  Tersulphide  of  Arsenic. 

a.  In  Solutions  of  Arsenious  Acid  or  Arsenites , free  from  Arsenic 
Acid. 

Precipitate  with  sulphuretted  hydrogen,  and  expel  the  excess  of  the 
precipitant  by  carbonic  acid,  conducting  the  process  in  the  same  way  as 
with  antimony — see  § 125,  1.  Wash  the  precipitated  tersulphide  of 
arsenic,  dry  at  100°,  and  weigh.  Particles  of  the  precipitate  adhe- 
ring so  firmly  to  the  glass  tube  that  mechanical  means  fail  to  remove 
them  are  dissolved  in  ammonia,  and  then  reprecipitated  by  hydrochloric 
acid.  For  the  properties  of  the  precipitate,  see  § 92.  The  results  are 
accurate. 

If  the  solution  contains  a substance  which  decomposes  sulphuretted 
hydrogen,  such  as  sesquioxide  of  iron,  chromic  acid,  &c.,  the  free  sul- 
phur which  precipitates  with  the  tersulphide  of  arsenic  destroys  the 
accuracy  of  the  results.  In  such  cases  the  precipitate  is  dissolved  in 
solution  of  potassa,  and  chlorine  transmitted  through  the  solution  (§ 
148,  II.  2,  b).  In  the  solution  produced,  which  contains  the  sulphur 
as  sulphuric  acid,  the  arsenic  as  arsenic  acid,  the  latter  is  determined  as 
in  2,  a ; or  the  sulphuric  acid  is  estimated,  the  quantity  found  calculated 
to  sulphur,  and  the  calculated  weight  of  the  latter  subtracted  from  that 
of  the  mixed  precipitate  of  tersulphide  of  arsenic  and  sulphur.  No  loss 
of  arsenic  by  volatilization  of  the  chloride  takes  place  in  this  method  of 
oxidizing  the  sulphide  of  arsenic,  since  the  solution  remains  alkaline. 
The  object  may  also  be  conveniently  attained  by  the  use  of  nitric  acid.  A 
very  strong  fuming  acid,  of  86°  boiling  point,  is  employed ; an  acid  of 
T42  sp.  gr.  which  boils  at  a higher  temperature  does  not  answer  the  pur- 
pose, as  the  separated  sulphur  would  fuse,  and  its  oxidation  would  be  much 
retarded.  The  well-dried  precipitate  is  shaken  into  a small  porcelain  dish, 
treated  with  a tolerably  large  excess  of  the  fuming  nitric  acid,  the  dish  im- 
mediately covered  with  a clock-glass,  and  as  soon  as  the  turbulence  of  the 
first  action  has  somewhat  abated,  heated  on  a water-bath,  till  all  the 
sulphur  has  disappeared,  and  the  nitric  acid  has  evaporated  to  a small 
volume.  The  filter  to  which  the  unremovable  traces  of  sulphide  of 
arsenic  adhere  is  treated  separately  in  the  same  manner,  the  complete 
destruction  of  the  organic  matter  being  finally  effected  by  gently  warm- 
ing the  somewhat  dilute  solution  with  chlorate  of  potassa  (Bunsen*). 
Or  the  filter  may  instead  be  extracted  with  ammonia,  the  solution 
evaporated  in  a separate  dish,  and  the  residual  tersulphide  treated  as 
above.  In  the  mixed  solution  the  arsenic  acid  is  finally  precipitated  as 
arseniate  of  magnesia  and  ammonia  (§  127,  2).  Treatment  of  the  impure 
precipitate  with  ammonia,  whereby  the  sulphide  is  dissolved,  and  the 
sulphur  is  supposed  to  remain  behind,  only  gives  approximate  results,  as 
the  ammoniacal  solution  of  tersulphide  of  arsenic  takes  up  a little  sul- 
phur. Small  quantities  of  admixed  free  sulphur  may  be  also  removed 
without  difficulty  by  bisulphide  of  carbon ; but  I cannot  recommend 
this  method  where  large  quantities  of  sulphur  are  to  be  extracted.  If 
the  precipitate  is  moist,  before  using  this  solvent,  the  water  should  bo 
got  rid  of  by  twice  treating  with  absolute  alcohol. 

b.  In  Solutions  of  Arsenic  Acid  or  Arseniates , or  of  a mixture  of  the 
two  Oxides  of  Arsenic. 


* Anna!,  d.  Chem.  u.  Pharm.  106,  10. 


254 


DETERMINATION. 


[§127. 

Heat  the  solution  in  a flask  (preferably  on  an  iron  plate)  to  about  70°, 
and  conduct  sulphuretted  hydrogen  at  the  same  time  into  the  fluid,  as 
long  as  precipitation  take  place.  The  precipitate  formed  is  always  a 
mixture  of  sulphur  and  tersulphide  of  arsenic,  since  the  arsenic  acid  is 
first  reduced  to  arsenious  acid  with  separation  of  sulphur,  and  then  the 
former  is  decomposed  (H.  Rose*). 

Only  in  the  case  wdien  a sulphosalt  containing  pentasulphide  of  arsenic 
is  decomposed  with  an  acid,  is  the  precipitate  actually  pentasulphide, 
and  not  merely  a mixture  of  sulphur  with  tersulphide  (A.  Fuchs  f). 
Whichever  may  be  the  constitution  of  the  precipitate,  either  the  arsenic 
or  the  sulphur  in  it  must  be  determined,  after  drying  and  weighing, 
by  one  of  the  methods  given  in  4,  a. 

5.  'Volumetric  Methods. 

a.  Method  which  presupposes  the  presence  of  Arsenious  Acid. 

Bunsen’s  method.];  If  bichromate  of  potassa  is  boiled  with  concen- 
trated hydrochloric  acid,  3 eq.  chlorine  are  disengaged  to  every  2 eq. 
chromic  acid  (2  Cr  03  + 6 H Cl=Cr2  Cl3  + 3 Cl + 6 H O).  But  if 
arsenious  acid  is  present  (not  in  excess)  there  is  not  the  quantity  of 
chlorine  disengaged  corresponding  to  the  chromic  acid,  but  so  much  less 
of  that  element  as  is  required  to  convert  the  arsenious  into  arsenic  acid 
(As  03H~2  Cl-f-2  H 0=As  05-f2  H Cl).  Consequently,  for  every  2 
eq.  chlorine  waqting  is  to  be  reckoned  1 eq.  arsenious  acid.  The  quan- 
tity of  chlorine  is  estimated  as  directed  130,  I.  d , 3. 

b.  Method , which  presupposes  the  presence  of  Arsenic  Acid. 

This  method  depends  on  the  precipitation  of  the  arsenic  acid  by  uranium 
solution  and  the  recognition  of  the  end  of  the  reaction  by  means  of  ferro- 
cyanide  of  potassium.  It  is  therefore  the  same  as  was  suggested  for  phos- 
phoric acid  by  Leconte,  and  brought  into  use  by  Neubauer,  § and  after- 
wards by  Pincus.  || 

Bodeker,®[  who  first  employed  the  process  for  arsenic  acid,  recommends 
the  employment  of  a solution  of  nitrate  of  sesquioxide  of  uranium,  as  this 
is  more  permanent  than  the  hitherto  used  acetate,  which  is  gradually 
decomposed  by  the  action  of  light. 

The  uranium  solution  has  the  correct  degree  of  dilution,  if  it  contains 
about  20  grm.  sesquioxide  of  uranium  in  1 litre.  It  should  contain  as  little 
free  acid  as  possible.  The  determination  of  its  value  may  be  effected 
with  the  aid  of  pure  arseniate  of  soda  or  by  means  of  arsenious  acid, — the 
latter  is  converted  into  arsenic  acid  by  boiling  with  fuming  nitric  acid. 
The  solution  is  rendered  strongly  alkaline  with  ammonia,  and  then  dis- 
tinctly acid  with  acetic  acid.  The  uranium  solution  is  now  run  in  from 
the  burette  slowly,  the  liquid  being  well  stirred  all  the  while,  till  a drop  of 
the  mixture  spread  out  on  a porcelain  plate,  gives  with  a drop  of  ferro- 
cyanide  of  potassium  placed  in  its  centre,  a distinct  reddish  brown  line 
where  the  two  fluids  meet.  The  height  of  the  fluid  in  the  burette  is  now 
read  off,  the  level  of  the  mixture  in  the  beaker  is  marked  with  a strip  of 
gummed  paper,  and  the  beaker  is  emptied  and  washed,  filled  with  water 

* Pogg.  Anna!.  107,  186.  f Zeitschmft  f.  anal.  Chem.  1,  189. 

X Anna!  d.  Chem.  u.  Pharm.  86,  290. 

§ Archiv.  fur  wissenschaftliche  Heilkunde,  Bd.  iv.  S.  228. 

U Journ.  f.  prakt.  Chem.  76,  104.  Tf  Anna!,  d.  Chem.  u.  Pharm.  117,  195. 


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§ 128-.l 


MOLYBDIC  ACID. 


255 


with  addition  of  about  as  much  ammonia  and  acetic  acid  as  was  before 
employed,  and  the  uranium  solution  is  cautiously  dropped  in  from  the 
burette,  till  a drop  taken  out  of  the  beaker  and  tested  as  above,  gives  an 
equally  distinct  border-line.  The  quantity  of  uranium  solution  used  in 
this  last  experiment  is  the  excess,  which  must  be  added  to  make  the  end- 
reaction  plain  for  the  dilution  adopted.  This  amount  is  subtracted  from 
that  used  in  the  first  experiment,  and  we  then  know  the  exact  value  of 
the  uranium  solution  with  reference  to  arsenic  acid. 

In  an  actual  analysis,  the  arsenic  is  first  brought  into  the  form  of  arsenic 
acid,  a clear  solution  is  obtained  containing  acetate  of  ammonia  and  some 
free  acetic  acid,*  and  the  process  is  conducted  exactly  as  in  determining 
the  value  of  the  standard  solution.  The  experiment  to  ascertain  the  cor- 
rection must  not  be  omitted  here,  otherwise  errors  are  sure  to  arise  from 
the  different  degrees  of  dilution  of  the  arsenic  acid  solutions  used  in  the 
determination  of  the  value  of  the  standard  solution  and  in  the  actual 
analyses.  The  results  of  two  determinations  of  arsenic  given  by  Bodeker 
are  satisfactory.  To  execute  the  method  well  requires  practice. 

6.  Estimation  of  Arsenious  Acid  by  Indirect  Gravimetric  Analysis. 

a.  Rose’s  method.  Add  to  the  hydrochloric  acid  solution,  in  the  pre- 
paration of  which  care  must  be  taken  to  exclude  oxidizing  substances,  a 
solution  of  sodio-  or  ammonio-terchloride  of  gold  in  excess,  and  digest  the 
mixture  for  several  days,  in  the  cold,  or,  in  the  case  of  dilute  solutions, 
at  a gentle  warmth  ; then  weigh  the  separated  gold  as  directed  in  § 123. 
Keep  the  filtrate  to  make  quite  sure  that  no  more  gold  will  separate.  2 
eq.  gold  correspond  to  3 eq.  arsenious  acid. 

b.  VoHL’sf  method.  Mix  the  solution  under  examination  with  a 
weighed  quantity  of  bichromate  of  potassa,  and  free  sulphuric  acid ; 
estimate  the  chromic  acid  still  present  by  the  method  given  in  § 130,  c, 
and  deduce  from  the  quantity  of  that  acid  consumed  in  the  process,  i.  e ., 
reduced  bv  the  arsenious  acid,  the  quantity  of  the  latter,  after  the  for- 
mula 3 As  03  + 4 Cr  03=3  As  06  + 2 Cr2  03. 

Supplement  to  the  Sixth  Group . 

§ 128. 

8.  Molybdic  Acid. 

Molybdic  acid  is  converted,  for  the  purpose  of  its  estimation,  either 
into  binoxide  of  molybdenum,  or  into  molybdate  of  lead,  or  into  bisul- 
phide of  molybdenum. 

a.  Pure  molybdic  acid  (Mo  03),  and  also  molybdate  of  ammonia,  may 
be  reduced  to  binoxide  by  heating  in  a current  of  hydrogen  gas.  This 
may  be  done  either  in  a porcelain  boat,  placed  in  a wide  glass  tube,  or 
in  a platinum  or  porcelain  crucible  with  perforated  cover  (§  108,  fig.  47, 
p.  181).  The  operation  is  continued  till  the  weight  remains  constant. 
The  temperature  must  not  exceed  a gentle  redness,  otherwise  the  binox- 
ide itself  might  lose  oxygen  and  become  partially  converted  into  metal. 


* Alkalies,  alkaline  earths  and  oxide  of  zinc  may  be  present,  but  not  such  metala 
as  yield  colored  precipitates  with  ferrocyanide  of  potassium,  as,  for  instance, 
copper. 

f Anal.  d.  Chem.  u.  Pharm.  94,  219. 


DETERMINATION. 


256 


L§  129. 


In  the  case  of  molybdate  of  ammonia  the  heat  must  be  very  low  at  first  on 
account  of  the  frothing. 

b.  The  following  is  the  best  method  of  precipitating  molybdic  acid  from 
an  alkaline  solution.  Dilute  the  solution,  if  necessary,  neutralize  the 
free  alkali  with  nitric  acid,  and  allow  the  carbonic  acid,  which  may  be 
liberated  in  the  process,  to  escape,  then  add  solution  of  neutral  nitrate 
of  suboxide  of  mercury.  The  yellow  precipitate  formed  appears  at  first 
bulky,  but  after  several  hours’  standing  it  shrinks ; it  is  insoluble  in  the 
fluid,  which  contains  an  excess  of  nitrate  of  suboxide  of  mercury.  Col- 
lect the  precipitate  on  a filter,  and  wash  with  a dilute  solution  of  nitrate 
of  suboxide  of  mercury,  as  it  is  slightly  soluble  in  pure  water.  Dry, 
remove  the  dry  precipitate  as  completely  as  practicable  from  the  filter, 
and  determine  the  molybdenum  in  it  as  directed  in  a (H.  Rose)  ; or  mix 
the  precipitate,  together  with  the  filter-ash,  with  a weighed  quantity  of 
ignited  oxide  of  lead,  and  ignite  until  all  the  mercury  is  expelled  ; then  add 
some  nitrate  of  ammonia,  ignite  again  and  weigh.  The  excess  obtained, 
over  and  above  the  weight  of  the  oxide  of  lead  used,  is  molybdic  acid 
(Seligsohn*). 

c.  The  precipitation  of  molybdenum  as  sulphide  is  always  a difficult 
operation.  If  the  acid  solution  is  supersaturated  with  sulphuretted 
hydrogen,  warmed,  and  filtered,  the  filtrate  and  washings  are  generally 
still  colored.  They  must,  accordingly,  be  warmed,  and  sulphuretted 
hydrogen  again  added,  and  the  operation  must  afterwards,  if  necessary, 
be  repeated  until  the  washings  appear  almost  colorless.  The  precipita- 
tion succeeds  better  when  the  sulphide  of  molybdenum  is  dissolved  in  a 
relatively  large  excess  of  sulphide  of  ammonium,  and,  after  the  fluid  has 
acquired  a reddish-yellow  tint,  precipitated  with  hydrochloric  acid. 
Zenker  f advises  then  to  boil,  until  the  sulphuretted  hydrogen  is  ex- 
pelled, and  to  wash  with  hot  water,  at  first  slightly  acidified.  The  brown 
sulphide  of  molybdenum  is  collected  on  a weighed  filter,  and  the  molyb- 
denum determined  in  an  aliquot  part  of  it,  by  gentle  ignition  in  a cur- 
rent of  hydrogen  gas,  as  in  a.  The  brown  sulphide  of  molybdenum 
changes  in  this  process  to  the  gray  bisulphide  (H.  Rose). 


II.  DETERMINATION  OF  ACIDS  IN  COMPOUNDS  CONTAINING 
ONLY  ONE  ACID,  FREE  OR  COMBINED AND  SEPARATION  OF 
ACIDS  FROM  BASES. 

FIRST  GROUP. 

First  Division. 

Arsenious  Acid — Arsenic  Acid — Chromic  Acid — (Selenious  Acid, 
Sulphurous  and  Hyposulphurous  Acids,  Iodic  Acid,  Nitrous  Acid). 

§129. 

1.  Arsenious  and  Arsenic  Acids. 

These  have  been  already  treated  of  among  the  bases  (§  127)  on  ac- 
count of  their  behavior  with  sulphuretted  hydrogen ; they  are  merely 


* Joum.  f . prakt.  Chem.  67,  472. 


f Ibid.  58,  259. 


CHROMIC  ACID. 


257 


§ 130.] 

mentioned  here  to  indicate  the  place  to  which  they  properly  belong. 
The  methods  of  separating  them  from  the  bases  will  be  found  in  Sec- 
tion V. 


§ 130. 

2.  Chromic  Acid. 

1.  Determination. 

Chromic  acid  is  determined  either  in  the  form  of  sesquioxide  of  chro- 
mium,,  or  in  that  of  chromate  of  lead . But  it  may  be  estimated  also 
from  the  quantity  of  carbonic  acid  disengaged  by  its  action  upon  oxalic 
acid  in  excess,  and  also  by  volumetric  analysis.  In  employing  the  first 
method,  it  must  be  borne  in  mind  that  1 eq.  sesquioxide  of  chromium 
corresponds  to  2 eq.  chromic  acid. 

a . Determination  as  Sesquioxide  of  Chromium. 

a.  The  chromic  acid  is  reduced  to  the  state  of  sesquioxide,  and  the 
amount  of  the  latter  determined  (§  106).  The  reduction  is  effected  either 
by  heating  the  solution  with  hydrochloric  acid  and  alcohol ; or  by  mixing 
hydrochloric  acid  with  the  solution,  and  conducting  sulphuretted  hydrogen 
into  the  mixture  ; or  by  adding  a strong  solution  of  sulphurous  acid,  and 
applying  a gentle  heat.  With  concentrated  solutions  the  first  method  is 
generally  resorted  to,  with  dilute  solutions  one  of  the  two  latter.  With 
respect  to  the  first  method,  I have  to  remark  that  the  alcohol  must  be 
expelled  before  the  sesquioxide  of  chromium  can  be  precipitated  with 
ammonia ; and  with  respect  to  the  second,  that  the  solution  supersaturated 
with  sulphuretted  hydrogen  must  be  allowed  to  stand  in  a moderately 
warm  place,  until  the  separated  sulphur  has  completely  subsided.  The 
results  are  accurate. 

j3.  The  neutral  or  slightly  acid  (nitric  acid)  solution  is  precipitated 
with  nitrate  of  suboxide  of  mercury,  the  red  precipitate  of  chromate  of 
suboxide  of  mercury  filtered  off,  washed  with  a dilute  solution  of  nitrate 
of  suboxide  of  mercury,  dried,  ignited,  and  the  residuary  sesquioxide  of 
chromium  weighed  (H.  Rose). 

b.  Determination  as  Chromate  of  Lead. 

The  solution  is  mixed  with  acetate  of  soda  in  excess,  and  acetic  acid 
added  until  the  reaction  is  strongly  acid  ; the  solution  is  then  precipitated 
with  neutral  acetate  of  lead.  The  washed  precipitate  is  either  collected 
on  a weighed  filter,  dried  in  the  water-bath,  and  weighed  ; or  it  is  gently 
ignited  as  directed  § 53,  and  then  weighed.  For  the  properties  of  the 
precipitate,  see  § 93,  2.  The  results  are  accurate. 

c.  Determination  by  means  of  Oxalic  Acid  (after  Voiil). 

When  chromic  acid  and  oxalic  acid  are  brought  together,  the  former 
yields  oxygen  to  the  latter  : sesquioxide  of  chromium  is  formed,  and  car- 
bonic acid  escapes  (2  Cr  03  -f  3 C2  03  = Cr3  03  -f  6 C 03).  Three  eq. 
carbonic  acid  (66)  correspond  accordingly  to  one  eq.  chromic  acid  (50*24). 
The  modus  operandi  is  the  same  as  in  the  analysis  of  manganese  ores 
(§215).  1 part  of  chromic  acid  requires  2\  parts  of  oxalate  of  soda.  If 

it  is  intended  to  determine  in  the  residue  the  alkali  which  was  combined 
with  the  chromic  acid,  oxalate  of  ammonia  is  used. 

17 


258 


DETERMINATION'. 


d.  Determination  by  Volumetric  Analysis. 

a.  Schwarz’s  method. 

The  principle  of  this  very  accurate  method  is  identical  with  that  upon 
which  Penny’s  method  of  determining  iron  is  based  (§  112,  2,  b).  The 
execution  is  simple  : acidify  the  not  too  dilute  solution  of  the  chromate 
with  sulphuric  acid,  add  in  excess  a measured  quantity  of  solution  of  prot- 
oxide of  iron,  the  strength  of  which  you  have  previously  ascertained, 
according  to  the  directions  of  § 1 12,  2,  a , or  6,  or  the  solution  of  a weighed 
quantity  of  sulphate  of  protoxide  of  iron  and  ammonia,  free  from  sesqui- 
oxide,  and  then  determine  in  the  manner  directed  § 112,  2,  a,  or  6,  the 
quantity  of  protoxide  of  iron  remaining.  The  difference  shows  the  amount 
of  iron  that  has  been  converted  by  the  chromic  acid  from  the  state  of  prot- 
oxide to  that  of  sesquioxide.  1 grm.  of  iron  corresponds  to  0*5981  of 
chromic  acid.  To  determine  the  chromic  acid  in  chromate  of  lead,  the 
latter  is,  after  addition  of  the  sulphate  of  protoxide  of  iron  and  ammonia, 
most  thoroughly  triturated  with  hydrochloric  acid,  water  added,  and  the 
analysis  then  proceeded  with. 

j3.  Bunsen’s  method.* 

If  a chromate  is  boiled  with  an  excess  of  fuming  hydrochloric  acid, 
there  are  disengaged  for  every  2 eq.  chromic  acid  3 eq.  chlorine ; for 
instance,  K O,  2 Cr  03  -f  7 H Cl  = K 01  + Cr2  Cl3  + 7 H O + 3 Cl.  If  the 
escaping  gas  is  conducted  into  solution  of  iodide  of  potassium  in  excess, 
the  3 eq.  chlorine  set  free  3 eq.  iodine.  By  determining  the  quantity  of 
the  latter  element  in  the  manner  described  in  § 146,  we  find  the  quantity 
of  the  chromic  acid;  381  of  iodine  corresponding  to  100*48  of  chromic 
acid. 

The  analytical  process  is  conducted  as  follows : — Put  the  weighed 
sample  of  the  chromate  (say  *3  to  *4  grm.)  into  the  little  flask  d,  fig.  51, 
(blown  before  the  lamp,  and  holding  only  from  36  to  40  c.  c.),  fill  the 

flask  to  two-thirds  with  pure 
fuming  hydrochloric  acid 
(free  from  Cl  and  S 02)  and 
connect  the  bulbed  evolution 
tube  a with  the  neck  of  the 
flask  by  means  of  a stout 
tight-closing  vulcanized  in- 
dia-rubber tube  c.  As  shown 
in  the  engraving,  a is  a bent 
pipette,  drawn  out,  at  the 
lower  end,  into  an  upturned 
point.  A loss  of  chlorine 
need  not  be  apprehended  on 
adding  the  hydrochloric  acid,  as  the  disengagement  of  that  gas  begins  only 
upon  the  application  of  heat.  Insert  the  evolution  tube  into  the  neck  of 
the  retort,  which  is  one-third  filled  with  solution  of  iodide  of  potassium,  f 
This  retort  holds  about  160  c.  c.  The  neck  presents  two  small  expan- 
sions, blown  before  the  lamp,  and  intended,  the  lower  one,  to  receive  the 
liquid  which  is  forced  up  during  the  operation,  the  upper  one,  to  serve  as 


* Anna!  d.  €hem.  u.  Pharm.  86,  279. 

f 1 part  of  pure  iodide  of  potassium,  free  from  iodic  acid,  dissolved  in  10  parts  of 
water.  The  fluid  must  show  no  brown  tint  immediately  after  addition  of  hydro- 
chloric acid. 


CHROMIC  ACID. 


259 


§ 130.] 

an  additional  guard  against  spirting.  Apply  heat  now,  cautiously,  to  the 
little  flask.  After  two  or  three  minutes’  ebullition,  the  whole  of  the 
chlorine  has  passed  over,  and  liberated  its  equivalent  quantity  of  iodine  in 
the  iodide  of  potassium  solution.  When  the  ebullition  is  at  an  end,  take 
hold  of  the  caoutchouc  tube  c with  the  left  hand,  and,  whilst  steadily 
holding  the  lamp  under  the  flask  with  the  right,  lift  a so  far  out  of  the 
retort  that  the  curved  point  is  in  the  bulb  b.  Now  remove  first  the  lamp, 
then  the  flask,  dip  the  retort  in  cold  water,  to  cool  it,  and  shake  the  fluid 
in  it  about  to  effect  the  complete  solution  of  the  separated  iodine  in  the 
excess  of  iodide  of  potassium  solution.  When  the  fluid  is  quite  cold, 
transfer  it  to  a beaker,  rinsing  the  retort  into  the  beaker,  and  proceed  as 
directed  § 146.  The  method  gives  very  satisfactory  results.  The  appa- 
ratus here  recommended  differs  slightly  from  that  used  by  Bunsen,  the 
retort  of  the  latter  having  only  one  bulbous  expansion  in  the  neck,  and 
the  evolution  tube  no  bulb,  being  closed  instead,  at  the  lower  end,  by  a 
glass  or  caoutchouc  valve,  which  permits  the  exit  of  the  gas  from  the  tube, 
but  opposes  the  entrance  of  the  fluid  into  it.  I think  the  modifications 
which  I have  made  in  Bunsen’s  apparatus  are  calculated  to  facilitate  the 
success  of  the  operation. 

II.  Separation  of  Chromic  Acid  from  the  Bases. 
a.  Of  the  First  Group 

a.  Reduce  the  chromic  acid  as  directed  in  I.,  and  separate  the  sesqui- 
oxide  of  chromium  from  the  alkalies  as  directed  in  § 155. 

£.  Mix  the  chromate  of  potassa  or  soda  with  about  2 parts  of  dry 
pulverized  chloride  of  ammonium,  and  heat  the  mixture  cautiously. 
The  residue  contains  the  chlorides  of  the  alkali  metals  and  sesquioxide 
of  chromium,  which  may  be  separated  by  means  of  water. 

y.  Chromate  of  ammonia  is  reduced  to  sesquioxide  of  chromium  by 
cautious  ignition.  The  ammonia  is  estimated  in  a separate  portion  ac- 
cording to  § 99,  3. 

6.  Of  the  Second  Group. 

a.  Fuse  the  compound  under  examination  with  4 parts  of  carbonate 
of  soda  and  potassa,  and  treat  the  fused  mass  with  hot  water,  which  dis- 
solves the  chromic  acid  in  the  form  of  an  alkaline  chromate.  The  resi- 
due contains  the  alkaline  earths  in  the  form  of  carbonates ; but  as  they 
contain  alkali,  they  cannot  be  weighed  directly.  The  chromic  acid  in  the 
solution  is  determined  as  in  I.  Chromate  of  baryta  (and  doubtless  also 
the  chromates  of  strontia  and  lime)  may,  as  shown  by  H.  Rose,*  be 
readily  and  completely  decomposed  by  simple  boiling  with  an  excess  of 
solution  of  carbonate  of  potassa  or  soda. 

j3.  Dissolve  in  hydrochloric  acid,  reduce  the  chromic  acid  according  to 
the  directions  of  I.,  a , and  separate  the  sesquioxide  of  chromium  from 
the  alkaline  earth  according  to  § 156. 

y.  Chromate  of  magnesia  as  well  as  other  chromates  of  the  alkaline 
earths  soluble  in  water  may  be  easily  decomposed  also,  by  determining 
the  chromic  acid  according  to  I.,  a , f3,  or  I.,  b,  and  separating  the  mag- 
nesia, <fcc.,  in  the  filtrate  from  the  excess  of  the  salt  of  mercury  or  lead 
as  directed  8 162. 


* Joum.  f.  prakt.  Chem.  66,  166. 


260 


DETERMINATION. 


[§  130- 


8.  Chromates  of  baryta,  strontia,  and  lime  may  also  be  decomposed  by 
the  method  described  II.,  a , j3.  Compare  Bahr,  analysis  of  bichromate 
of  baryta,  lime,  &c.* 

c.  Of  the  Third  Group. 

a.  From  Alumina. 

Precipitate  the  alumina  by  ammonia  or  carbonate  of  ammonia  (§  105), 
and  determine  the  chromic  acid  in  the  filtrate  according  to  the  directions 
given  in  I.  (compare  also  § 157). 

ft.  From  Sesquioxide  of  Chromium. 

an.  Determine  in  one  portion  the  quantity  of  the  chromic  acid  accord- 
ing to  I.,  c,  or  I.,  <7,  a,  or  ,3,  and  in  another  portion  the  total  amount  of 
the  chromium,  by  converting  it  all  into  either  sesquioxide  or  chromic 
acid.  The  entire  conversion  of  the  substance  into  sesquioxide  may  be 
effected  either  by  cautious  ignition  with  chloride  of  ammonium,  or  ac- 
cording to  I.,  a , — into  chromic  acid  according  to  § 106,  2. 

bb.  In  many  cases  the  chromic  acid  may  be  precipitated  according  to 
I.,  a , |3,  or  I.,  b.  The  sesquioxide  of  chromium  and  suboxide  of  mercury, 
or  oxide  of  lead,  in  the  filtrate,  are  separated  as  directed  § 162. 

cc.  The  hydrated  compounds  of  sesquioxide  of  chromium  with  chromic 
acid,  such  as  are  obtained  by  precipitating  a solution  of  sesquioxide  of 
chromium  with  a solution  of  chromate  of  potassa,  &c.,  may  also  be  ana- 
lyzed by  ignition  in  a stream  of  dry  air,  the  apparatus,  fig.  25,  p.  45, 
being  employed.  The  loss  of  weight  of  the  bulb-tube  represents  the 
joint  amount  of  oxygen  and  water  that  have  escaped.  If  the  increment 
of  the  Ca  Cl  tube  is  deducted,  we  shall  have  the  oxygen.  Now  every 
3 eq.  oxygen  correspond  to  2 eq.  of  chromic  acid.  The  amount  of  the 
latter  being  thus  calculated,  we  have  only  to  subtract  its  equivalent 
quantity  of  sesquioxide  from  the  weight  of  residue  after  the  ignition, 
and  the  remainder  is  the  quantity  of  sesquioxide  originally  present. 
Vogel  f and  also  Storer  and  Elliot  J have  employed  this  method. 

d.  Of  the  Fourth  Group. 

a.  Proceed  as  directed  in  b , a.  Upon  treating  the  fused  mass  with 
hot  water,  the  metals  are  left  as  oxides.  In  the  case  of  manganese  the 
fusion  must  be  effected  in  an  atmosphere  of  carbonic  acid  gas.  Appara- 
tus, fig.  47  in  § 108. 

|3.  Deduce  the  chromic  acid  as  directed  in  I.,  a , and  separate  the  ses- 
quioxide of  chromium  from  the  metals  in  question,  as  directed  in  § 160. 

e.  Of  the  Fifth  and  Sixth  Groups. 

a.  Acidify  the  solution,  and  precipitate,  either  at  once  or  after  pre- 
vious reduction  of  the  chromic  acid  by  sulphurous  acid,  with  sulphuret- 
ted hydrogen.  The  metals  of  the  fifth  and  sixth  groups  precipitate  in 
eonj unction  with  free  sulphur  (§§  115  to  127),  the  chromic  acid  is 
reduced.  Flter  and  determine  the  sesquioxide  of  chromium  in  the  fil- 
trate, as  directed  in  I.,  a. 

(3.  Chromate  of  lead  may  be  conveniently  decomposed  by  heating 


* Joum.  f.  prakt.  Chem.  60,  60. 
f Ibid.  77,  484. 

X Proceedings  of  the  American  Academy,  vol.  v.  p.  198. 


SELENIOUS  ACID. 


261 


§ 131.] 


with  hydrochloric  acid  and  some  alcohol ; the  chloride  of  lead  and  ses- 
quichloride  of  chromium  formed  are  subsequently  separated  by  means 
of  alcohol  (compare  § 162).  The  alcoholic  solution  ought  always  to  be 
tested  with  sulphuric  acid ; should  a precipitate  of  sulphate  of  lead  form, 
this  must  be  filtered  off,  weighed,  and  taken  into  account  (compare  also 
§130,  l.,d). 


Supplement  to  the  First  Division. 

§ 131- 

1.  Selenious  Acid. 

From  aqueous  or  hydrochloric  acid  solutions  of  selenious  acid,  the  sele- 
nium is  precipitated  by  sulphurous  acid  gas  or,  in  presence  of  an  excess 
of  acid,  by  sulphite  of  soda,  or  sulphite  of  ammonia.  If  the  solution 
contains  nitric  acid,  this  must  be  removed  first  by  evaporation  with 
hydrochloric  acid.  The  precipitated  liquid  is  heated  to  boiling  for  £ 
hour,  which  changes  the  precipitate  from  its  original  red  color  to  black, 
and  makes  it  dense  and  heavy.  The  liquid  is  tested  by  a further  addi- 
tion of  the  reagent  to  see  whether  any  more  selenium  will  separate ; the 
precipitate  is  finally  collected  on  a weighed  filter,  dried  at  a temperature 
somewhat  below  100°,  and  weighed.  Since  H.  Rose  * has  shown  that 
the  presence  of  hydrochloric  acid  is  an  essential  condition  to  the  com- 
plete reduction  of  the  selenious  acid,  the  former  acid  must  be  added,  if 
not  already  present.  To  make  quite  sure  that  all  the  selenium  has 
been  removed,  the  filtrate  is  evaporated  to  a small  volume,  boiled  with 
strong  hydrochloric  acid,  so  as  to  reduce  any  selenic  acid  to  selenious 
acid,  and  tested  once  more  with  sulphurous  acid. 

As  regards  the  separation  of  selenious  acid  from  the  bases,  the  follow- 
ing brief  directions  will  suffice : — ■ 

a.  If  the  bases  are  not  liable  to  be  altered  by  the  action  of  sulphurous 
acid  and  hydrochloric  acid,  the  selenium  may  be  at  once  precipitated  in 
the  way  just  given;  the  filtrate,  when  evaporated  with  sulphuric  acid, 
yields  the  base  as  sulphate. 

b.  From  bases  which  are  not  thrown  down  from  acid  solution  by 
hydrosulphuric  acid,  the  selenious  acid  may  be  separated  by  sulphuretted 
hydrogen.  The  precipitate  is,  according  to  H.  Rose,  a mixture  of  1 eq. 
selenium  with  2 eq.  sulphur.  If  it  is  dried  at  or  a little  below  100°, 
the  weight  of  the  selenium  may  be  accurately  ascertained.  Should,  how- 
ever, extra  sulphur  be  mixed  with  the  precipitate,  the  latter  is  oxidized 
while  still  moist  with  hydrochloric  acid  and  chlorate  of  potassa,  or  by 
treatment  with  potassa  solution  with  simultaneous  heating  and  trans- 
mission of  chlorine.  It  is  necessary  here  to  oxidize  the  sulphur  com- 
pletely, as  it  may  inclose  selenium.  The  solution  now  containing  selenic 
acid  is  heated  until  it  smells  no  longer  of  chlorine,  hydrochloric  acid  is 
added,  and  the  mixture  is  reheated.  The  selenic  acid  is  hereby  reduced 
to  selenious  acid,  and  when  the  solution  has  again  ceased  to  smell  of 
chlorine,  the  selenium  is  precipitated  with  sulphurous  acid. 

c.  In  many  selenites  or  selenates  the  selenium  may  also  be  determined, 
by  converting  first  into  selenocyanide  of  potassium,  and  precipitating 
the  aqueous  solution  of  the  latter  with  hydrochloric  acid  (Oppenheim  f). 


* Zeitschrift  f.  analyt.  Chem.  1,  73. 


f Journ  f.  prakt.  Chem.  71,  280. 


262 


DETERMINATION. 


To  this  end  the  substance  is  mixed  with  7 or  8 times  its  quantity  of  ordi- 
nary cyanide  of  potassium  (containing  cyanic  acid),  the  mixture  is  put 
into  a long-necked  flask,  or  a porcelain  crucible,  covered  with  a layer  of 
cyanide  of  potassium,  and  fused  in  a stream  of  hydrogen.  The  tempera- 
ture is  kept  so  low  that  the  glass  or  porcelain  is  not  attacked,  and  while 
cooling  care  must  be  taken  to  exclude  atmospheric  air.  When  cold,  the 
brown  mass  is  treated  with  water,  and  the  colorless  solution  filtered,  if 
necessary.  The  liquid  should  be  somewhat  but  not  immoderately  diluted. 
Now  boil  some  time  (in  order  to  convert  the  small  quantity  of  selenide 
of  potassium  that  may  be  present  into  selenocyanide  of  potassium  by  the 
excess  of  cyanide  of  potassium),  allow  to  cool,  supersaturate  with  hydro- 
chloric acid,  and  heat  again  for  some  time.  At  the  end  of  12  or  24 
hours  all  selenium  will  have  separated,  filter,  dry  at  100°,  and  weigh. 
The  results  obtained  by  this  process  are  accurate  (H.  Rose  *). 

If  the  selenium  agglomerates  together  on  heating,  it  may  inclose  salts. 
In  such  cases,  by  way  of  control,  it  should  be  redissolved  in  nitric  acid, 
and,  after  addition  of  hydrochloric  acid,  precipitated  with  sulphurous  acid. 
The  fluid  filtered  off  from  the  selenious  precipitate  is,  as  a rule,  free  from 
selenium  ; it  is,  however,  always  well  to  satisfy  one’s  self  on  this  point 
by  the  addition  of  sulphurous  acid. 

d.  From  many  bases  the  selenious  acid  (and  also  the  selenic  acid)  may 
be  separated  by  fusing  the  compound  with  2 parts  of  carbonate  of  soda 
and  1 part  of  nitrate  of  potassa,  extracting  the  fused  mass  thoroughly 
by  boiling  with  water,  saturating  the  filtrate,  if  necessary,  with  carbonic 
acid,  to  free  it  from  lead  which  it  might  contain,  then  boiling  down  with 
hydrochloric  acid  in  excess  (to  reduce  the  selenic  acid  and  drive  off 
the  nitric  acid),  and  precipitating  finally  with  sulphurous  acid. 

Selenium,  if  pure,  must  volatilize  without  residue  when  heated  in  a 
tube. 

2.  Sulphurous  Acid. 

To  estimate  free  sulphurous  acid  in  a fluid  which  may  contain  also 
other  acids  (sulphuric  acid,  hydrochloric  acid,  acetic  acid),  a weighed 
quantity  of  the  fluid  is  diluted  with  water,  absolutely  free  from  air,f 
until  the  diluted  liquid  contains  not  more  than  0'05  per  cent,  by  weight 
of  sulphurous  acid  ; some  starch-paste  is  now  added,  and  then  standard 
solution  of  iodide,  until  the  iodide  of  starch  reaction  makes  its  appear- 
ance. The  reaction,  which,  under  these  circumstances,  takes  place  is 
represented  by  the  equation 

1 + II  O-fS  02=H  I+S  03  (Bunsen). 

1 equivalent  of  iodine  added  corresponds  accordingly  to  1 equivalent  of 
sulphurous  acid.  For  the  details  of  the  process  I refer  to  § 146.  In 
the  case  of  sulphites  soluble  in  water  or  acids,  water  perfectly  free  from 
air  is  poured  over  the  substance  under  examination,  in  sufficient  quan- 
tity to  attain  the  degree  of  dilution  stated  above,  sulphuric  or  hydro- 
chloric acid  added  in  excess,  and  then  starch-paste  and  solution  of  iodine 
as  above.  The  greatest  care  must  be  taken  in  this  method,  to  use,  for 
the  purpose  of  dilution,  water  absolutely  from  air. 

Sulphurous  acid  may  also  be  determined  in  the  gravimetric  way,  by 

* Zeitschrift  f.  analyt.  Chem.  1,  73. 

T Prepared  by  long-continued  boiling  and  subsequent  cooling  with  exclusion 
of  air. 


NITROUS  ACID. 


263 


§ 131.] 

conversion  into  sulphuric  acid,  and  precipitation  of  the  latter  with 
baryta,  according  to  the  directions  of  § 132.  This  method  is  especially 
applicable  in  the  case  of  sulphites  quite  free  from  sulphuric  acid.  The 
conversion  of  the  sulphurous  into  sulphuric  acid  is  effected  in  the  wet 
way  best  by  saturating  the  fluid  with  chlorine,  and  warming ; in  the  dry 
way,  by  heating  the  salt,  in  a platinum  crucible,  with  4 parts  of  a mix- 
ture of  equal  parts  of  carbonate  of  soda  and  nitrate  of  potassa. 

3.  Hyposulphurous  Acid. 

Hyposulphurous  acid,  in  form  of  soluble  hyposulphites,  may  be  deter- 
mined by  means  of  iodine,  in  a similar  way  to  sulphurous  acid.  The 
reaction  is  represented  by  the  equation 

2 (Na  0,S2  02)  + I=rNaO,  S405+Nal. 

The  salt  under  examination  is  dissolved  in  a large  amount  of  water, 
starch-paste  added,  and  then  solution  of  iodine  until  the  blue  color 
makes  its  appearance.  That  this  method  can  give  correct  results  only 
in  cases  where  no  other  substances  acting  upon  iodine  are  present, 
need  hardly  be  mentioned.  In  the  case  of  dilute  fluids  the  results  do  not 
vary,  if  the  fluid  is  acidified  before  adding  the  solution  of  iodine,  and 
the  operation  proceeded  with  so  quickly  that  no  time  is  left  for  the  free 
hyposulphurous  acid  to  decompose  into  sulphur  and  sulphurous  acid 
(Fr.  Mohr  *).  Hyposulphurous  may  be  converted  into  sulphuric  acid 
and  then  determined  : the  process' is  the  same  as  for  sulphurous  acid. 

4.  Iodic  Acid. 

Iodic  acid  may  be  determined  by  the  following  easy  method  : — distil 
the  acid,  in  the  free  state  or  in  combination  with  a base,  with  an  excess  of 
pure  fuming  hydrochloric  acid,  in  the  apparatus  described  in  § 130,  d , j3 
(chromic  acid),  receive  the  disengaged  chlorine  in  solution  of  iodide  of 
potassium,  and  determine  the  separated  iodine  as  directed  in  § 130,  d , p. 
As  1 eq.  iodic  acid  sets  free  4 eq.  chlorine,  and  consequently  4 eq.  iodine, 
you  have  to  reckon  167  of  iodic  acid  for  508  of  iodine.  The  decompo- 
sition of  iodic  acid  by  hydrochloric  acid  is  represented  by  the  equation 
I 05  + 5 H Cl  = IC1  + 5 H O 4-  4 Cl  (Bunsen  f). 

5.  Nitrous  Acid. 

Nitrous  acid  may  be  determined  very  satisfactorily  with  a solution  of 
pure  permanganate  of  potassa,  provided  the  fluid  be  sufficiently  diluted  to 
prevent  the  nitrous  acid,  which  is  liberated  by  the  addition  of  a stronger 
acid,  being  decomposed  by  water  with  formation  of  nitric  acid  and  nitric 
oxide.  For  1 part  of  anhydrous  nitrous  acid,  at  least  5000  parts  of  water 
should  be  present.  The  decomposition  is  represented  by  the  following 
equation : — 5 NOa  4-  2 Mn2  07  = 5 N 05  -f  4 Mn  O.  If  the  permanganate 
be  standardized  with  iron  dissolved  to  protoxide,  4 eq.  iron  correspond  to 
1 eq.  N03,  since  both  of  these  require  2 eq.  oxygen.  Nitrites  are  dis- 
solved in  very  slightly  acidulated  water,  the  permanganate  is  added  till  the 
oxidation  of  the  nitrous  acid  is  nearly  completed,  the  solution  is  then  made 
strongly  acid,  and  finally  permanganate  is  added  to  light-red  coloration. 

To  determine  hyponitric  acid  in  red  fuming  nitric  acid,  transfer  a few  c.  c. 
to  about  500  c.  c.  cold  pure  distilled  water  with  stirring,  and  determine  the 


* Lehrbuch  der  Titrirmethode,  Nachtriige,  S.  384. 
f Annal.  d.  Chem.  u.  Pharm.  86,  285. 


264 


DETERMINATION. 


[§  132. 


nitrous  acid  produced.  1 eq.  nitrous  acid  found  corresponds  to  2 eq.  hypo- 
nitric  acid,  for  the  latter — when  mixed  with  such  a large  quantity  of  water 
as  is  indicated  above — is  decomposed  in  accordance  with  the  following 
equation : — 2 N 04  + 2 H O — HO,  N05  + HO,NOs  (Sig.  Feldhaus  *). 

As  regards  the  estimation  of  nitrous  acid  with  binoxide  of  lead,  comp. 
op.  cit.  p.  431 ; also  Lang’s  observations,  idem,  p.  484. 

Second  Division  of  the  First  Group  of  the  Acids . 

Sulphuric  Acid  ; (Hydrofluosilicic  Acid). 

§ 132. 

Sulphuric  Acid. 

I.  Determination. 

Sulphuric  acid  is  usually  determined  in  the  gravimetric  way  as  sulphate 
of  baryta.  The  acid  may,  however,  be  estimated  also  by  certain  volu- 
metric methods,  based  upon  the  insolubility  of  this  salt  (and  the  sulphate 
of  lead). 

1.  Gravimetric  Method. 

Add  to  the  sufficiently  dilute  solution,  if  necessary,  some  hydrochloric 
acid  to  acid  reaction,  heat  to  near  ebullition,  add  chloride  of  barium  in 
slight  excess,  and  proceed  as  directed  § 101,  1,  a.  The  washing  is  always 
best  effected  by  decantation  first.  Should  the  analyzed  solution  contain 
nitric  acid,  some  nitrate  of  baryta  is  likely  to  precipitate  in  conjunction 
with  the  sulphate ; the  removal  of  this  admixture  of  nitrate  of  baryta 
from  the  precipitate  requires  protracted  washing  with  hot  water.  It  is, 
under  all  circumstances,  necessary  to  continue  the  washing  of  the  pre- 
cipitate until  the  last  washings  remain  perfectly  clear  upon  testing  with 
sulphuric  acid.  In  cases  where  perfect  accuracy  is  desirable  I would  re- 
commend the  following  proceeding.  After  igniting  the  precipitate  accord- 
ing to  the  directions  of  § 53,  and  weighing,  moisten  it  with  a few  drops 
of  hydrochloric  acid,  add  hot  water,  stir  with  a very  thin  glass  rod  or  with 
a platinum  wire,  rinse  the  rod  or  wire,  and  warm  gently  for  some  time. 
Pour  the  almost  clear  fluid  on  to  a small  filter,  and  test  the  filtrate  with 
sulphuric  acid.  If  this  produces  turbidity  or  a precipitate,  which  is  a 
sign  that  the  sulphate  contains  an  admixture  of  another  baryta  salt,  wash 
the  residue  again  with  hot  water,  until  the  washings  are  no  longer  ren- 
dered turbid  by  sulphuric  acid.  Dry  now  the  precipitate  in  the  crucible, 
together  with  the  small  filter,  burn  the  latter  on  the  lid,  heat  to  redness, 
and  weigh.  If  the  sulphuric  acid  has  been  precipitated  from  a solution 
containing  much  nitric  acid  or  much  alkaline  salt,  the  testing  of  the 
ignited  precipitate  is  not  merely  to  be  recommended,  but  it  is  absolutely 
necessary,  since  in  such  cases  it  is  by  no  means  unlikely  that  the  sulphate 
of  baryta  will  contain  1 per  cent,  or  more  of  nitrate  of  baryta  or  alkaline 
salt.  The  results  are  not  always  so  exact  as  used  to  be  believed.  If 
precipitated  in  very  acid  solutions  a little  of  the  sulphate  of  baryta  remains 
dissolved.  If  precipitated  in  very  saline  solutions,  ofi  the  other  hand,  the 
results  are  generally  too  high,  since  it  is  difficult  in  this  case  to  obtain  a 
pure  precipitate. 

The  sulphate  of  baryta  has  a great  tendency  to  carry  salts  (especially 


Zeitschrift  f.  analyt.  Chem.  1,  426. 


SULPHURIC  ACID. 


265 


§ 132.] 

nitrates  and  chlorides)  down  with  it,  which  cannot  be  removed  at  all  by 
washing,  and  are  removed  but  imperfectly  often  when  the  ignited  precipi- 
tate is  treated  with  hydrochloric  acid  and  water.* * * §  Fr.  Stolba  \ recom- 
mends treatment  with  a solution  of  acetate  of  copper  for  the  purification  of 
impure  sulphate  of  baryta,  and  demonstrates  the  accuracy  of  his  process 
by  numerous  analyses,  which  were  performed  purposely  under  disadvan- 
tageous circumstances,  ^.e.,  in  the  presence  of  much  alkali-  and  baryta- 
salt.  The  solution  of  acetate  of  copper  is  prepared  from  the  crystallized 
salt  of  the  shops ; if  it  contains  no  sulphuric  acid,  add  2 drops  of  the 
dilute  acid.  Dissolve  it  with  addition  of  a little  acetic  acid  in  hot  water, 
add  a few  drops  of  solution  of  chloride  of  barium,  enough  to  give  a slight 
baryta  reaction,  boil  a short  time  and  filter.  The  solution  on  cooling  de- 
posits crystals  ; the  supernatant  cold  saturated  solution  is  employed.  The 
small  addition  of  chloride  of  barium  to  the  solution  of  copper  containing 
a little  sulphuric  acid,  is  for  the  purpose  of  incapacitating  the  fluid  for 
taking  up  any  sulphate  of  baryta,  by  saturating  it,  so  to  speak,  with  that 
substance. 

After  the  precipitation  of  the  sulphuric  acid  has  been  effected  in  the 
usual  manner  in  the  fluid  acidified  with  hydrochloric  acid  and  the  precipi- 
tate has  been  washed  by  decantation  combined  with  filtration,  till  the 
filtrate  ceases  to  give  a reaction  for  baryta  and  chlorine  (at  least  for  baryta), 
trea/t  the  precipitate  still  in  the  beaker  with  40  or  50  c.  c.  of  the  copper 
solution,  add  some  water  and  acetic  acid,  and  digest  at  a temperature  near 
the  boiling  point  for  10  or  15  minutes,  with  constant  agitation.  The 
acetic  acid  added  should  be  sufficient  to  prevent  the  precipitation  of  basic 
salt  during  this  operation.  If,  notwithstanding  the  precaution  taken,  basic 
salt  is  precipitated,  it  must  be  redissolved  by  addition  of  acetic  acid  (not 
hydrochloric  acid).  After  the  precipitate  has  been  filtered  off  and  washed 
with  hot  water,  drop  a few  drops  of  hydrochloric  acid  on  it,  continue 
washing,  lastly  dry,  ignite,  and  weigh. 

[Sulphate  of  baryta  may  be  purified,  when  its  bulk  is  not  too  large,  by 
dissolving  in  the  crucible,  after  ignition,  in  pure  concentrated  and  hot 
sulphuric  acid.  On  diluting  copiously  with  water,  the  sulphate  sepa- 
rates and  may  be  washed  with  hot  water. J] 

2.  Volumetric  Methods. 

a.  After  Carl  Mohr.§  Make  a standard  solution  by  dissolving  1 eq. 
(i.e.,  12T96  grm.)  pure  cystallized  chloride  of  barium  (Ba  Cl  + 2 aq.) 
to  1 litre.  Add  to  the  fluid  to  be  examined  for  sulphuric  acid — which, 
should  it  contain  much  free  acid,  is  previously  to  be  nearly  neutralized 
with  pure  carbonate  of  soda — a measured  quantity  of  fhis  solution,  best 
a round  number  of  cubic  centimetres,  in  more  than  sufficient  proportion 
to  precipitate  the  sulphuric  acid,  but  not  in  too  great  excess.  Digest  the 
mixture  for  some  time  in  a warm  place,  then  precipitate,  without  previous 
filtration,  the  excess  of  chloride  of  barium  with  carbonate  of  ammonia 
and  a little  caustic  ammonia,  filter  off  the  precipitate  consisting  of 
sulphate  and  carbonate  of  baryta,  wash  uutil  the  water  running  off  acts 
no  longer  upon  sensitive  red  litmus  paper,  and  then  determine  the  carbo* 


* Comp.  Zeitschrift  f.  analyt.  Chem.  1,  80. 

f Ding,  polyt.  Journ.  168,  43  ; Zeitschrift  f.  analyt.  Chem.  2,  390. 

% [The  Ed.  cannot  name  the  originator  of  this  method,  having  mislaid  his  refe- 
rence. ] 

§ Anna!,  d.  Chem.  u.  Pharm.  90,  165. 


266 


DETERMINATION. 


[§  132. 

nate  of  baryta  in  tbe  precipitate  by  the  alkalimetric  method  given  in 
§ 210.  By  deducting  the  quantity  of  baryta  found  in  the  state  of  carbo- 
nate from  that  corresponding  to  the  chloride  of  barium  added,  you  find 
the  amount  of  baryta  equivalent  to  the  sulphuric  acid  present.  Suppose 
you  have  added  to  the  fluid  under  examination — 

10  c.  c.  of  chloride  of  barium  solution  = 0*765  Ba  O, 
and  found,  at  the  end  of  the  process, 

0*300  of  carbonate  of  baryta  = 0*233  “ 

the  remainder,  0*532  Ba  O, 

will  give  you  the  quantity  of  the  sulphuric  acid  by  means  of  the  pro- 
portion : 

76*5  : 40  : : 0*532 : a ; cc  =0*278  (S  03). 

This  calculation  may  be  considerably  simplified,  by  estimating  the  car- 
bonate of  baryta,  as  stated  in  § 210,  by  means  of  a normal  solution  of 
nitric  acid  ; of  which  it  consequently  takes  a volume  equal  to  that  of  the 
chloride  of  barium  solution  to  neutralize  the  carbonate  of  baryta  precipi- 
tated from  the  latter,  if  no  sulphuric  acid  is  present;  if,  on  the  other  hand, 
that  acid  is  present,  less  of  the  nitric  acid  solutionis  required,  the  difference 
expressing  the  quantity  of  sulphuric  acid.  In  the  above  example  it  took 
3*04  c.  c.  to  neutralize  the  carbonate  of  baryta  formed ; deducting  these 
from  the  10  c.  c.  used,  we  have  left  6*96  c.  c. 

1000  : 6*96  : : 40  : x;  a =0*278  (S  03). 

The  results  of  this  method  are  quite  satisfactory,  if  the  solution  does 
not  contain  too  much  free  acid ; but  in  presence  of  a large  excess  of 
free  acid,  the  action  of  the  salt  of  ammonia  will  retain  carbonate  of 
baryta  in  solution,  which,  of  course,  will  make  the  amount  of  sulphuric 
acid  appear  higher  than  is  really  the  case.  That  this  method  is  alto- 
gether inapplicable  in  presence  of  phosphoric  acid,  oxalic  acid,  or  any 
other  acid  precipitating  baryta  salt  from  neutral  solutions,  need  hardly  be 
mentioned. 

b.  After  It.  Wildenstein  (second  process*).  Of  all 
the  methods  for  the  volumetric  estimation  of  sulphuric 
acid,  the  simplest,  and  that  which  is  capable  of  the  most 
general  application,  is  to  drop  into  the  solution  con- 
taining excess  of  hydrochloric  acid,  standard  chloride  of 
barium  solution,  till  the  exact  point  is  reached  when 
no  more  precipitation  takes  place.  This  point  is  diffi- 
cult to  hit,  and  hence  the  method  has  only  found  a very 
limited  use. 

Wildenstein  has  given  this  method  a practical  form 
which  renders  it  possible  to  complete  an  analysis  in  about 
half  an  hour,  and  at  the  same  time  to  obtain  satisfactory 
results.  He  employs  the  apparatus,  fig.  68.  A is  a 
bottle  of  white  glass  whose  bottom  has  been  removed, 
it  contains  900 — 950  c.  c.  J3  is  a strong  funnel  tube, 
with  bell-shaped  funnel,  and  bent  as  shown,  provided  below  with  a 
piece  of  india-rubber  tube,  a screw  compression-cock,  and  a small  piece 


Fig.  68. 


* Zeitschrift  f.  analyt.  Chem.  1,  432. 


§ 132.] 


SULPHUKIC  ACID. 


267 


of  tubing  not  drawn  out.  The  length  from  c to  d is  about  7^-8,  from 
d to  e about  12  cm.  The  opening  of  the  funnel-tube/*,  which  may  with 
advantage  have  a diameter  of  2*5  to  3 cm.  is  covered  as  follows  : — Take 
a piece  of  fine  new  woollen  stuff  or  muslin,  free  from  sulphuric  acid, 
and  about  6 cm.  square,  lay  on  it  two  pieces  of  Swedish  paper  of  the 
same  size,  and  then  another  piece  of  stuff  like  the  first,  now  bind  these 
all  together  over  the  opening  f,  carefully  and  without  injuring  the  paper, 
by  means  of  a strong  linen  thread  which  has  been  drawn  a few  times 
over  wax,  and  cut  it  off  even  all  round.  We  have  now  a small  syphon- 
filter,  which  enables  us  to  filter  off  a portion  of  fluid  contained  in  A,  and 
turbid  from  sulphate  of  baryta,  clear  and  with  comparative  rapidity. 

On  gradually  adding  chloride  of  barium  to  the  dilute  acid  solution  of 
a sulphate  a point  occurs  which  may  be  compared  to  the  neutral  point 
in  precipitating  silver  with  chloride  of  sodium  (see  p.  211) ; i.  e .,  there 
is  a certain  moment,  when  a portion  filtered  off  will  give  a turbidity 
both  with  sulphuric  acid  and  chloride  of  barium  after  the  lapse  of  a few 
minutes.  On  this  account  we  must  either  proceed  on  the  principle 
recommended  for  the  estimation  of  silver,  i.  e.,  disregarding  the  quantity 
of  chloride  of  barium  in  the  solution,  to  standardize  it  by  adding  it  to 
a known  amount  of  a sulphate,  till  a precipitate  ceases  to  be  formed  ; or 
else  we  must — and  Wildenstein  recommends  this  latter  course — con- 
sider as  the  end-point  of  the  reaction  the  point  at  which  chloride  of 
barium  ceases  to  produce  a distinctly  visible  precipitation  in  the  clear 
filtrate  after  a lapse  of  two  minutes. 

The  chloride  of  barium  solution  is  prepared  by  dissolving  61  grm.  Ba  Cl 
+ 2 aq.  in  a litre  of  water  ; 1 c.  c.  corresponds  to  *02  sulphuric  acid. 

First  prepare  the  solution  of  the  sulphate  to  be  analyzed  (using 
about  3 or  4 grm.),  then  fill  A with  warm  water,  open  the  cock  with 
the  screw  or  by  the  aid  of  a glass  rod,  and  wait  till  the  syphon  13  is 
quite  full  of  water.  If  the  water  runs  down  the  tube  c e without  filling 
it  entirely,  close  and  open  the  cock  a few  times,  and  this  inconvenience 
will  be  removed.  (It  is  not  allowable  to  suck  at  e,  or  to  fill  the  syphon 
with  the  wash-bottle  at  e,  as  either  proceeding  would  inevitably  lead  to 
injuring  the  filter.)  Now  close  the  cock  and  pour  out  the  warm  water, 
replace  it  by  400  c.  c.  of  boiling  water,  add  the  ready-prepared  solution 
of  the  sulphate,  and  a suitable  quantity  of  hydrochloric  acid,  if  necessary, 
and  run  in  the  chloride  of  barium  solution,  at  first  in  rather  large  por- 
tions, at  last  in  ^ c.  c.  Before  each  fresh  addition  of  chloride  of  barium 
open  the  cock  and  allow  rather  more  liquid  to  flow  into  a beaker  than 
corresponds  to  the  contents  of  the  syphon.  This  quantity  should  be  pre- 
viously ascertained,  and  a mark  indicating  it  made  on  the  beaker.  Now 
close  the  cock  and  pour  the  filtrate  without  loss  back  into  A.  (As  the 
beaker  is  used  over  and  over  again  for  the  same  purpose  it  need  not  be 
rinsed  out.)  Now  run  some  of  the  fluid  into  a test  tube,  so  as  to  one- 
third  fill  it,  add  to  the  clear  fluid  2 drops  of  chloride  of  barium  from  the 
burette  and  shake.  If  a precipitate  or  turbidity  is  produced  return  the 
portion  to  the  main  quantity.  The  experiment  is  finished  when  the  last 
portion  tested  shows  after  the  lapse  of  exactly  two  minutes  no  distinctly 
visible  turbidity.  The  drops  of  chloride  of  barium  used  for  the  last 
testing  are  of  course  not  reckoned.  The  slight  error  involved  from 
the  fact  that  the  small  quantity  of  fluid  in  the  syphon  is  finally  unacted 
on,  is  too  small  to  be  noticed.  During  the  experiment  the  filter  must 
not  be  injured  by  the  stirring.  In  case  the  point  has  been  overstepped. 


268 


DETERMINATION. 


[§  132. 

add  1 c.  c.  of  dilute  sulphuric  acid  (equivalent  to  the  chloride  of  barium) 
to  A , and  endeavor  to  hit  the  end-point  again.  Here  1 c.  c.  will  have  to 
be  subtracted  from  the  c.  c.  of  chloride  of  barium  used. 

The  results  obtained  by  Wildenstein  are  of  sufficient  accuracy  for 
technical  purposes.  Some  experiments  made  in  my  own  laboratory 
were  also  quite  satisfactory. 

II.  Separation  of  Sulphuric  Acid  from  the  Bases. 

a . From  those  Bases  with  which  the  Acid  forms  Compounds  solu- 

ble in  Water  or  in  Hydrochloric  Acid. 

Precipitate  the  sulphuric  acid  as  in  I.  The  filtrate  which  contains, 
besides  the  bases  originally  combined  with  the  sulphuric  acid,  also  the 
excess  of  the  chloride  of  barium  used,  is  treated  by  the  methods  given  in 
Section  V.  to  effect  the  separation  of  the  bases  in  question  from  baryta. 

b.  From  those  Bases  with  which  the  Acid  forms  Compounds  in- 

soluble or  difficultly  soluble  in  Water  or  in  Hydrochloric 
Acid. 

a.  From  Baryta , Strontia , and  Lim,e. 

Fuse  the  finely  pulverized  compound  under  examination  in  a pla- 
tinum crucible,  with  5 parts  of  mixed  carbonates  of  soda  and  potassa.  Put 
the  crucible,  with  its  contents,  into  a beaker,  or  into  a platinum  or  por- 
celain dish,  pour  water  over  it,  and  apply  heat  until  the  alkaline  sul- 
phates and  carbonates  are  completely  dissolved  ; filter  the  hot  solution 
from  the  residuary  carbonates  of  the  earths,  wash  the  latter  thoroughly 
with  water,  to  which  a little  ammonia  and  carbonate  of  ammonia  has 
been  added,  and  determine  according  to  §§  101  to  103.  If  the  precipi- 
tates have  been  well  washed,  it  is  perfectly  admissible  to  ignite  and 
weigh  at  once.  Precipitate  the  sulphuric  acid  from  the  filtrate,  as  in  I. 
Finely  pulverized  sulphate  of  lime  and  sulphate  of  strontia  may  be  com- 
pletely decomposed  also  by  boiling  with  a solution  of  carbonate  of  potas- 
sa ; * the  same  process  will  answer  also  for  sulphate  of  baryta;  but  the 
operation  is  far  more  difficult,  and  complete  decomposition  is  effected 
only  by  boiling  the  precipitate,  after  decanting  the  fluid  repeatedly  with 
an  excess  of  solution  of  carbonated  alkali  (H.  Bose  f).  [Sulphate  of  lime 
may  be  dissolved  in  moderately  dilute  hydrochloric  acid,  and  the  sul- 
phuric acid  precipitated  with  chloride  of  barium.] 

j 3.  From  Oxide  of  Lead. 

The  simplest  way  of  effecting  the  decomposition  of  sulphate  of  lead 
consists  in  digesting  it,  at  the  common  temperature,  with  a solution  of 
bicarbonate  of  soda  or  potassa,  filtering,  washing  the  precipitate,  deter- 
mining the  sulphuric  acid  in  the  filtrate,  as  in  I.,  dissolving  the  precipi- 
tate, which  contains  alkali,  in  nitric  acid  or  acetic  acid,  and  determin- 
ing the  lead  in  the  solution  by  one  of  the  methods  given  in  § 162. 

Presence  of  strontia  and  lime  necessitates  no  alteration  in  this 
method ; but  if  baryta  also  is  present,  and  it  is  accordingly  necessary  to 
ignite  J the  mixture  with  carbonated  alkalies  (or  to  boil  repeatedly 
with  fresh  portions  of  solution  of  the  same),  a small  portion  of  lead  al- 
ways remains  in  solution  in  the  alkaline  fluid ; this  must  be  precipitated 
by  passing  carbonic  acid  before  filtering. 


* Carbonate  of  soda  does  not  answer  as  well. 

f Joum.  f.  prakt.  Chem.  64,  382,  and  65,  316. 

if  This  ignition  is  most  safely  effected  in  a porcelain  crucible. 


§§  133,  134.] 


PHOSPHORIC  ACID. 


269 


Supplement  to  the  Second  Division . 


§ 133. 

Hydrofluosilicic  Acid. 

If  you  have  hydrofluosilicic  acid  in  solution,  add  solution  of  chloride 
of  potassium,  or  chloride  of  sodium,  then  a volume  of  strong  alcohol 
equal  to  the  fluid  present,  collect  the  precipitated  silicofluoride  of  potas- 
sium or  sodium  on  a weighed  filter,  and  wash  with  a mixture  of  equal 
volumes  of  spirit  of  wine  and  water.  Dry  the  washed  precipitate  at 
100°,  and  weigh.  Mix  the  alcoholic  filtrate  with  hydrochloric  acid, 
evaporate  to  dryness,  and  treat  the  residue  with  hydrochloric  acid  and 
water.  If  this  leaves  an  undissolved  residue  of  silicic  acid,  this  is  a sign 
that  the  examined  acid  contained  an  excess  of  silicic  acid ; the  weight 
of  the  residue  shows  the  amount  of  the  excess. 

Silicofluoride  of  potassium  has  the  formula  K FI,  Si  FL,  silicofluoride 
of  sodium,  Na  FI,  Si  Fl2.  Both  compounds  are  anhydrous  at  100°. 
They  dissolve  with  difficulty  in  water,  and  are  insoluble  in  dilute  spirit 
of  wine.  The  analysis  of  silicofluorides  of  metals  is  best  effected  by  heat- 
ing in  platinum  vessels,  with  concentrated  sulphuric  acid ; fluoride  of 
silicon  and  hydrofluoric  acid  volatilize,  the  bases  are  left  behind  in  the 
form  of  sulphates,  and  may,  in  many  cases,  after  volatilization  of  the  ex- 
cess of  sulphuric  acid,  be  weighed  as  such.  If  the  metallic  silicofluo- 
rides to  be  analyzed  contain  water,  mix  them  most  intimately  with  6 
parts  of  recently  ignited  oxide  of  lead  (H.  Bose),  cover  the  mixture,  in 
a small  retort,  with  a layer  of  pure  oxide  of  lead,  weigh  the  retort,  heat 
cautiously  until  the  contents  begin  to  fuse  together,  remove  the  aque- 
ous vapor  still  remaining  in  the  vessel  by  suction,  and  weigh  the  retort 
again  when  cold.  The  diminution  of  weight  shows  the  quantity  of  water 
expelled.  Do  not  neglect  testing  the  drops  of  the  escaping  water  with 
litmus  paper  ; the  result  is  accurate  only  if  they  have  no  acid  reaction ; 
compare  § 35,  ft. 

Third  Division  of  the  First  Group  of  the  A.cids. 

Phosphoric  Acid — Boracic  Acid — Oxalic  Acid — Hydrofluoric 

Acid. 

§ 134. 

1.  Phosphoric  Acid. 

I.  Determination. 

Tribasic  phosphoric  acid  may  be  determined  in  a great  variety  of 
ways.  The  forms  in  which  this  determination  may  be  effected  have 
been  given  already  in  § 93,  4.  The  most  appropriate  forms  for  the  pur- 
pose, however,  are  pyrophosphate  of  magnesia  and  phosphate  of  sesqui- 
oxide  of  uranium .,  because  they  are  in  themselves  well  worthy  of  recom- 
mendation and  can  be  employed  in  almost  all  cases.  The  determination 
as  pyrophosphate  of  magnesia  is  frequently  preceded  by  precipitation  in 
another  way,  especially  as  phospho-molybdate  of  ammonia,  occasionally  as 
phosphate  of  binoxide  of  tin.  The  other  forms  in  which  phosphoric 


DETERMINATION. 


270 


[§  134. 


acid  may  be  determined  give  also,  in  part,  very  good  results,  but  admit 
only  of  a more  limited  application. 

With  regard  to  meta-  and  pyro-phosphoric  acids,  I have  simply  to 
remark  here  that  these  acids  cannot  be  determined  by  any  of  the 
methods  given  below.  The  best  way  to  effect  their  determination  is  to 
convert  them  into  tribasic  phosphoric  acid  ; as  follows  : — 

a.  In  the  dry  way.  By  protracted  fusion  with  from  4 to  6 parts  of 
mixed  carbonates  of  soda  and  potassa.  This  method  is,  however,  appli- 
cable only  in  the  case  of  meta-  and  pyro-phosphates  of  the  alkalies,  and 
of  those  meta-  or  pyro-phosphates  of  metallic  oxides  which  are  completely 
decomposed  by  fusion  with  alkaline  carbonates  ; it  fails,  accordingly,  for 
instance,  with  the  salts  of  alkaline  earths,  magnesia  excepted. 

/3.  In  the  wet  way.  The  salt  is  heated  for  some  time  with  a strong 
acid,  best  with  concentrated  sulphuric  acid  (Weber*).  This  method 
leads  only  to  the  attainment  of  approximate  results,  in  the  case  of  all 
salts  whose  bases  form  soluble  compounds  with  the  acid  added,  since  in 
these  cases  the  meta-  or  pyro-phosphoric  acid  is  never  completely  liber- 
ated ; but  the  desired  result  may  be  fully  attained  by  the  use  of  any 
acid  which  forms  insoluble  compounds  with  the  bases  present.  Respect- 
ing the  partial  conversion  in  the  former  case,  I have  found  that  it  ap- 
proaches the  nearer  to  completeness  the  greater  the  quantity  of  free  acid 
added,  f and  that  the  ebullition  must  be  long-continued  (comp.  Expt. 
No.  36). 

It  must  be  borne  in  mind  that  tribasic  phosphoric  acid  changes,  at  a 
temperature  still  below  150°,  to  pyro-phosphoric  acid ; thus,  for  instance, 
upon  evaporating  common  phosphate  of  soda  with  hydrochloric  acid  in 
excess,  and  drying  the  residue  at  150°,  we  obtain  Na  01+  Na  O,  H O,  P 06. 

a.  Determination  as  Phosphate  of  Lead. 

Proceed  as  with  arsenic  acid,  § 127,  1 ( i.e .,  evaporate  with  a weighed 
quantity  of  oxide  of  lead,  and  ignite).  This  method  presupposes  that  no 
other  acid  is  present  in  the  aqueous  or  nitric  acid  solution  ; it  has  this 
great  advantage  that  it  gives  correct  results,  no  matter  whether  the  phos- 
phoric acid  present  is  mono-,  bi-,  or  tribasic. 

b.  Determination  as  Pyrophosphate  of  Magnesia. 

a.  Direct  determination  (suitable  in  all  cases  in  which  it  is  quite  certain 
that  the  acid  is  present  in  the  tribasic  state,  either  free  or  combined  with 
an  alkali). 

Add  to  the  solution  a clear  mixture  of  sulphate  of  magnesia,  chloride 
of  ammonium,  and  ammonia  (see  § 63,  6),  as  long  as  a precipitate  continues 
to  form  ; should  the  solution  not  yet  evolve  a strong  ammoniacal  odor,  add 
some  more  ammonia ; let  the  mixture  stand  1 2 — 24  hours,  without  applying 
heat,  the  glass  being  covered,  filter,  wash  the  crystalline  precipitate  with 
a mixture  of  3 parts  of  water  and  1 part  of  solution  of  ammonia,  until  the 
washings,  after  the  addition  of  nitric  acid,  are  no  longer  rendered  turbid 
by  nitrate  of  silver,  and  proceed  afterwards  exactly  as  directed  in  § 104,  2. 
The  results  are  very  accurate  (Expt.  No.  89).  The  loss  sustained  from  the 
slight  solubility  of  the  basic  phosphate  of  magnesia  and  ammonia  is  very 
trifling  (Expt.  No.  32),  and  may  even  be  altogether  corrected  by  measuring 


* Pogg.  Annal.  73,  137. 

\ There  are,  however,  other  considerations  which  forbid  going  too  far  in  this 
respect. 


PHOSPHORIC  ACID. 


£71 


§ 134-1 

the  fill, rate,  and  adding  for  every  54  c.  c.  0*001  grm.  pyiophosphate  of 
magnesia.  For  the  properties  of  the  precipitate  and  residue,  see  § 74. 
If  the  solution  contains  pyrophosphoric  acid,  the  precipitate  is  flocculent, 
and  dissolves  in  ammoniated  water  (Weber). 

1 3 . Indirect  determination , with  previous  precipitation  as  phospho- 
molybdate  of  ammonia,  Sonnestschein.*  (Applicable  in  all  cases  in  which 
the  phosphoric  acid  is  present  in  the  tribasic  state,  even  in  presence  of 
alkaline  earths,  alumina,  sesquioxide  of  iron,  &c.  Tartaric  acid,  however, 
and  similarly  acting  organic  substances  must  be  absent.) 

The  molybdenum  solution  described  in  the  “ Qual.  Anal.,”  p.  66,  is 
employed  as  the  precipitant.  The  fluid  to  be  examined  for  phosphoric  acid 
should  be  concentrated,  it  may  contain  free  nitric  acid  or  sulphuric  acid. 
Hydrochloric  acid  and  chlorides,  if  present,  must  be  removed  by  repeated 
evaporation  with  strong  nitric  acid.  Transfer  it  to  a beaker  and  add  a 
considerable  quantity  of  the  molybdenum  solution, — about  40  parts  molyb- 
dic  acid  must  be  added  for  every  1 part  phosphoric  acid, — stir,  without 
touching  the  sides,  and  keep  covered  12  or  24  hours  in  a warm  place  (not 
hotter  than  40°).  Then  remove  a portion  of  the  clear  supernatant  fluid 
with  a pipette,  mix  it  with  an  equal  volume  of  molybdenum  solution,  and 
allow  it  to  stand  some  time  at  40°.  If  a further  precipitation  takes  place, 
return  the  portion  to  the  main  quantity,  add  more  molybdenum  solution, 
allow  to  stand  again  12  to  24  hours  and  test  again. \ When  complete  pre- 
cipitation has  been  effected,  transfer  the  precipitate  to  a small  filter,  remove 
the  rest  from  the  beaker  by  means  of  portions  of  the  filtrate,  and  wash  the 
precipitate  with  a mixture  of  100  parts  of  molybdenum  solution,  20  of  nitric 
acid,  sp.  gr.  1*2,  and  80  of  water,  which  should  be  dropped  on  in  small 
quantities.  Then  dissolve  the  precipitate  in  ammonia  on  the  filter,  wash 
the  latter,  neutralize  a portion  of  the  ammonia  in  the  filtrate  with  hydro- 
chloric acid  (the  solution  must  of  course  still  remain  strongly  ammoniacal 
and  clear),  and  precipitate  with  magnesia  mixture  (compare  a).  The 
results  are  accurate. 

As  this  method  requires  so  large  a quantity  of  molybdic  acid,  it  is  usually 
resorted  to  only  in  cases  where  methods  b , a,  and  c are  inapplicable  ; and 
the  amount  of  phosphoric  acid  in  the  quantity  of  substance  taken  to  operate 
upon  is  not  allowed  to  exceed  0*  1 grm.  Arsenic  acid  and  silicic  acid,  J if  pre- 
sent, must  first  be  removed.  Of  all  the  methods  for  determining  phosphoric 
acid  in  the  presence  of  sesquioxide  of  iron  and  alumina,  this  is  the  best. 

y.  Indirect  determination , with  previous  precipitation  as  phosphate  of 
binoxide  of  tin. 

After  Girard. § Dissolve  the  substance  in  which  the  phosphoric  acid 

* Journ.  f.  prakt  Chem.  53,  343. 

f [If  the  molybdic  solution  contain,  as  it  should,  5 per  cent,  of  molybdic  acid, 
the  addition  of  12  c.  c.  for  every  centigramme  of  phosphoric  acid  (60  parts  of 
molybdic  to  1 part  of  phosphoric  acid)  will  insure  complete  precipitation.  ] 

\ Silicic  acid  may  also  be  thrown  down,  in  form  of  a yellow  precipitate,  by  acid 
solution  of  molybdate  of  ammouia,  especially  in  presence  of  much  chloride  of 
ammonium  (W.  Knop,  Chem.  Centralb.  1857,  691).  Mr.  Grundmann,  who  repeated 
Knop’s  experiments  in  my  laboratory,  obtained  the  same  results.  The  precipitate 
dissolves  in  ammonia.  If  the  solution,  after  addition  of  some  chloride  of  ammo- 
nium, is  allowed  to  stand  for  some  time,  the  silicic  acid  separates,  and  the  phos- 
phoric acid  may  then  be  precipitated  from  the  filtrate  with  magnesia-mixture  ; it 
is,  however,  always  the  safer  way  to  remove  silicic  acid  first. 

S [ This  is  a modification  of  the  method  of  Reissig  (Ann.  Chem.  u.  Ph.  98,  339) 
founded  upon  that  of  Reynoso  (Joum.  f.  prakt.  Chem.  54,  261).  The  observa 
tions  of  Baeber  (Fres.  Zeit.  iv. , 122)  have  been  regarded.] 


272 


DETERMINATION. 


[§  134. 

is  to  be  estimated  in  highly  concentrated  nitric  acid,  remove  all  chlorine, 
either  by  precipitation  with  nitrate  of  silver,  or  by  repeated  evaporation 
with  nitric  acid,  add  at  least  eight  times  as  much  tinfoil  as  there  is 
phosphoric  acid  present,  and  warm  the  mixture  for  five  or  six  hours, 
until  the  precipitate  has  completely  subsided,  leaving  the  supernatant 
fluid  clear.  Wash  with  hot  water  by  decantation  8 to  10  times,  and 
finally  by  filtration. 

The  precipitate,  consisting  of  metastannic  acid  and  phosphate  of  binoxide 
of  tin,  together  with  a little  phosphate  of  sesquioxide  of  iron  and  of  alumina, 
is  heated  with  sulphide  of  ammonium  in  excess,  digested  about  two  hours, 
and  then  filtered ; the  precipitate,  consisting  of  sulphide  of  iron  and  hy- 
drate of  alumina,  is  washed  with  water  to  which  a little  sulphide  of  am- 
monium has  been  added,  dissolved  in  nitric  acid,  and  the  solution  thus 
formed  mixed  with  the  filtrate  from  the  tin  precipitate  which  contains 
the  principal  quantity  of  the  bases.  From  the  sulphide  of  ammonium 
filtrate,  which  contains  bisulphide  of  tin  and  phosphate  of  ammonia,  the 
phosphoric  acid  is  at  once  precipitated  by  magnesia-mixture.  I may  add 
that  Girard  considers  4 to  5 parts  tin  sufficient  for  1 part  phosphoric 
acid.  The  results  afforded  by  his  test  analyses  are  unexceptionable. 

c.  Determination  as  Phosphate  of  Sesquioxide  of  Uranium. 

After  Leconte,  A.  Arendt,  and  W.  Knop  * (very  suitable  in  pres- 
ence of  alkalies  and  alkaline  earths,  but  not  in  presence  of  any  notable 
amount  of  alumina ; in  presence  of  sesquioxide  of  iron,  the  method  can 
be  applied  only  with  certain  modifications,  see  § 135,  g,  y).  Where  it 
is  possible,  prepare  an  acetic  acid  solution  of  the  salt.  If  you  have  a 
nitric  or  hydrochloric  acid  solution,  remove  the  greater  portion  of  the 
free  acid  by  evaporation,  add  ammonia  until  red  litmus  paper  dipped  in- 
to it  turns  very  distinctly  blue,  and  then  redissolve  the  precipitate 
formed  in  acetic  acid.  If  mineral  acids  were  present,  add  also  some  ace- 
tate of  ammonia.  Mix  the  fluid  now  with  solution  of  acetate  of  sesqui- 
oxide of  uranium,  and  heat  the  mixture  to  boiling,  which  will  cause  the 
phosphoric  acid  to  separate,  in  form  of  yellow  phosphate  of  sesquioxide 
of  uranium  and  ammonia. 

Wash  the  precipitate,  first  by  decantation,  boiling  up  each  time,  then 
by  filtration ; the  operation  may  be  materially  facilitated  by  adding, 
immediately  after  precipitation,  as  soon  as  the  liquid  has  cooled  a little, 
2 or  3 drops  of  chloroform,  and  giving  the  mixture  a vigorous  shake,  or 
boiling  it  once  or  twice.  Dry  the  precipitate,  and  ignite  as  directed 
§ 53.  It  is  advisable  to  evaporate  small  quantities  of  nitric  acid  on  the 
ignited  precipitate  repeatedly,  and  to  re-ignite.  The  residue  must  have 
the  color  of  the  yolk  of  an  egg.  For  the  properties  of  the  precipitate 
and  residue,  see  § 93,  4,  e.  Should  it  be  necessary  to  dissolve  the 
ignited  residue  again,  for  the  purpose  of  reprecipitating  it,  this  can  be 
done  only  after  fusing  it  with  a large  excess  of  mixed  carbonates 
of  soda  and  potassa,  and  thereby  converting  the  pyrophosphoric  into  tri- 
basic  phosphoric  acid.  Results  accurate  ; compare  the  proofs  given  by 
the  authors,  and  Expt.  No.  90. 

* Leconte  was  the  first  to  recommend  the  method  of  precipitating  phosphoric 
acid  from  acetic  acid  solutions  by  means  of  a salt  of  uranium  ( Jahresb.  von  Lie- 
big und  Kopp,  far  1853,  642) ; A.  Arendt  and  W.  Knop  have  subsequently  sub- 
jected it  to  a careful  and  searching  examination  (Chem.  Centralbl.  1856,  769, 
803  ; and  1857,  177). 


PHOSPHORIC  ACID. 


273 


§ 134.] 

d.  Determination  as  Dasic  Phosphate  of  Sesquioxide  of  Iron. 

a.  Proceed  exactly  as  in  the  determination  of  arsenic  acid,  by  v. 
Kobell’s  modification  of  Berthier’s  method  (§  127,  3,  b).  The  results 
are  accurate. 

3.  Mix  the  acid  fluid  containing  the  phosphoric  acid  with  an  excess 
of  solution  of  sesquichloride  of  iron  of  known  strength,  or  with  a weighed 
quantity  of  ammonia  iron-alum,  add,  if  necessary,  sufficient  alkali  to  neu- 
tralize the  greater  portion  of  the  free  acid,  mix  with  acetate  of  soda  in 
excess,  and  boil.  If  the  quantity  of  solution  of  sesquichloride  of  iron 
added  was  sufficient,  the  precipitate  must  be  brownish-red.  This  pre- 
cipitate consists  of  basic  phosphate  and  basic  acetate  of  sesquioxide  of 
iron,  and  contains  the  whole  of  the  phosphoric  acid  and  of  the  sesquiox- 
ide of  iron.  Filter  off  boiling,  wash  with  boiling  water  mixed  with 
some  acetate  of  ammonia,  dry  carefully,  and  ignite  in  a platinum  cruci- 
ble with  access  of  air  (§  53).  Moisten  the  residue  left  upon  ignition 
with  strong  nitric  acid,  evaporate  this  at  a gentle  heat,  and  ignite  again. 
Should  this  operation  have  increased  the  weight,  which,  however,  is  not 
usually  the  case,  it  must  be  repeated,  until  the  weight  remains  constant. 
Deduct  from  the  weight  of  the  residue  that  of  the  sesquioxide  of  iron 
contained  in  the  solution  added  ; the  difference  is  the  phosphoric  acid. 

y.  ( J.  Weeren’s  method,  suitable  for  the  estimation  of  the  phosphoric 
acid  in  phosphates  of  the  alkalies  and  alkaline  earths.* * * §)  Mix  the  nitric 
acid  solution  of  the  phosphate  under  examination,  which  must  contain  no 
other  strong  acid,  with  a solution  of  nitrate  of  sesquioxide  of  iron  of  known 
strength,  in  sufficient  proportion  to  insure  the  formation  of  a basic  salt ; 
evaporate  the  mixture  to  dryness,  heat  the  residue  to  160°,  until  no  more 
nitric  acid  fumes  escape,  treat  with  hot  water  until  all  nitrates  of  the  alkalies 
and  alkaline  earths  are  removed, j-  collect  the  yellow-ochreous  precipitate 
on  a filter,  dry,  ignite  (see  § 53),  weigh,  and  deduct  from  the  weight  the 
quantity  of  sesquioxide  of  iron  added. 

e.  Determination  as  Dasic  Phosphate  of  Magnesia  (3  Mg  O,  P 05). 

(Fr.  Schulze’s  method,  suitable  more  particularly  to  effect  the  sepa- 
ration of  phosphoric  acid  from  alkalies. J) 

Mix  the  solution  of  the  alkaline  phosphate,  which  contains  chloride  of 
ammonium,  with  a weighed  excess  of  pure  magnesia,  evaporate  to  dryness, 
ignite  the  residue  until  the  chloride  of  ammonium  is  expelled,  and  separate 
the  magnesia,  which  is  still  present  in  form  of  chloride  of  magnesium,  by 
ignition  with  oxide  of  mercury.  Treat  the  ignited  residue  with  water,  fil- 
ter the  solution  of  the  chlorides  of  the  alkali  metals,  wash  the  precipitate, 
dry,  ignite,  and  weigh.  The  excess  of  weight  over  that  of  the  magnesia 
used  shows  the  quantity  of  the  phosphoric  acid.  Results  satisfactory. 

f Determination  by  Volumetric  Analysis. 

1.  With  Uranium  Solution. 

The  employment  of  this  solution  was  recommended  twelve  years  ago  by 
Leconte.  § Neubauer  |J  improved  the  method  and  described  it  in  detail, 

* Joum.  f.  prakt.  Chem.  67,  8. 

f In  presence  of  magnesia,  warming  with  a solution  of  nitrate  of  ammonia  ia 
advisable. 

X Journ.  f.  prakt.  Chem.  63,  440. 

§ Jahresber.  von  Liebig  u.  Kopp,  fiir  1853,  642. 

| Archiv  fiir  wissenschaftliche  Ileilkunde,  iv.  228. 

18 


274 


DETERMINATION. 


and  afterwards  it  was  recommended  again  by  Pincus,*  and  subsequently 
by  BoDEKER.f  The  principle  of  the  method  is  as  follows : acetate  of  ses- 
quioxide  of  uranium  precipitates  from  solutions  rendered  acid  by  acetic 
acid,  phosphate  of  sesquioxide  of  uranium,  or — in  the  presence  of  considera- 
ble quantities  of  ammoniacal  salts — phosphate  of  sesquioxide  of  uranium 
and  ammonia.  The  proportion  between  the  uranium  and  the  phosphoric 
acid  is  the  same  in  both  compounds.  Both  compounds  when  freshly  pre- 
cipitated and  suspended  in  water  are  left  unchanged  by  ferrocyanide  of 
potassium ; acetate  of  sesquioxide  of  uranium,  on  the  other  hand,  is  indica- 
ted by  this  reagent  with  great  delicacy,  insoluble  reddish-brown  ferrocya- 
nide of  uranium  being  precipitated. 

According  to  Neubauer  J the  following  solutions  are  employed  : — 

a.  A Solution  of  Phosphoric  Acid  of  known  strength. 

Prepared  by  dissolving  10*085  grm.  pure,  crystallized,  uneffloresced, 
powdered,  and  pressed  phosphate  of  soda  in  water  to  1 litre.  50  c.  c. 
contain  0*1  grm.  P05. 

h.  An  Acid  Solution  of  Acetate  of  Soda. 

Prepared  by  dissolving  100  grm.  acetate  of  soda  in  900  water,  and 
adding  ordinary  acetic  acid  to  1 litre. 

c.  A Solution  of  Acetate  of  Sesquioxide  of  Uranium  (§  63,  3)  in  water. 

This  is  standardized  by  means  of  the  phosphate  of  soda  solution.  1 c.c. 
indicates  *005  grm.  P G5.  The  solution  is  made  at  first  a little  stronger 
than  necessary,  so  that  it  may  contain  in  the  litre  say  22  grm.  Ur2  03 
(corresponding  to  32*5  grm.  Ur2  03,  A + 2 aq.  or  34  grm.  Ur2  03,  A + 3 
aq.),  its  value  is  determined,  and  it  is  diluted  accordingly.  To  determine 
its  value  proceed  as  follows  : transfer  50  c.  c.  of  the  a solution  to  a beaker, 
add  5 c.  c.  of  the  b solution,  and  heat  in  a water-bath  to  90 — 100°.  Now 
run  in  uranium  solution,  at  first  a large  quantity,  at  last  in  ^ c.  c.,  testing 
after  each  addition  whether  the  precipitation  is  finished  or  not.  For  this 
purpose  spread  out  one  or  two  drops  of  the  mixture  on  a white  porcelain 
surface  and  introduce  into  the  middle,  by  means  of  a thin  glass  rod,  a 
small  drop  of  ferrocyanide  of  potassium  solution.  As  soon  as  a trace  of 
excess  of  acetate  of  uranium  is  present,  a reddish-brown  spot  forms  in 
the  drop,  which,  surrounded  as  it  is  by  the  colorless  or  almost  colorless 
fluid,  may  be  very  distinctly  perceived.  When  the  final  reaction  has  just 
appeared,  heat  a few  minutes  in  the  water-bat^  and  repeat  the  testing 
on  the  porcelain.  If  now  the  reaction  is  still  plain  the  experiment  is 
concluded.  If  the  uranium  solution  had  been  exactly  of  the  required 
strength,  20  c.  c.  would  have  been  used ; but  'it  is  actually  too  concen- 
trated,, hence  less  than  20  c.  c.  must  have  been  used.  Suppose  it  was  18 
c.  c.,  then  the  solution  will  be  right,  if  for  every  18  c.  c.  we  add  2 c.  c. 
of  water.  If  in  this  first  experiment  we  find  that  the  solution  is  much 
too  strong,  the  solution  is  diluted  with  somewhat  less  water  than  is 
properly  speaking  required,  another  experiment  is  made,  and  it  is  then 
diluted  exactly. 

The  actual  analysis  must  be  made  under  as  nearly  as  possible  similar 
circumstances  to  those  under  which  the  standardizing  of  the  uranium  solu- 
tion was  performed,  especially  as  regards  the  acetate  of  soda.  This  salt 
retards  the  precipitation  of  uranium  by  ferrocyanide  of  potassium,  hence 


* Journ.  f.  prakt.  Chem.  76,  104.  f Annal.  d.  Chem.  u.  Pharm.  117,  195. 
% Anleitunjr  zur  Harnanalyse,  4 Aufl.  S.  148. 


§ 135-1 


PHOSPHORIC  ACID. 


275 


the  test  drop  on  the  porcelain  plate  becomes  darker  and  darker.  The 
analyst  should  accustom  himself  to  observing  the  first  appearance  of  the 
slightest  brownish  coloration  in  the  middle  of  the  drop,  and  should  take 
this  as  the  end-reaction.  It  need  hardly  be  added  that  the  same  person 
must  make  the  analysis  who  has  standardized  the  solution  (Neubauer). 

The  method  is  applicable  to  solutions  of  free  phosphoric  acid,  and  to 
alkaline  and  alkaline  earthy  phosphates,  but  cannot  be  employed  in 
presence  of  sesquioxide  of  iron  and  alumina.  Dissolve  the  substance  in 
water  or  the  least  possible  quantity  of  acetic  acid,  add  5 c.  c.  of  b solution, 
dilute  to  50  c.  c.,  proceed  with  the  addition  of  uranium  as  above,  and 
count  *005  grm.  P 05  for  every  c.  c.  used.  The  results  are  satisfactory. 

II.  Separation  of  Phosphoric  Acid  from  the  Bases. 

§ 135. 

a.  From,  the  Alkalies  (see  also  d,  h,  k). 

a.  Add  chloride  of  ammonium,  then  acetate  of  lead,  exactly,  till  no 
more  precipitate  is  produced,  filter  off  the  precipitate  consisting  of  phos- 
phate and  chloride  of  lead,  wash,  precipitate  from  the  filtrate  the  slight 
excess  of  lead  by  sulphuretted  hydrogen,  filter  and  evaporate  with  hy- 
drochloric acid  (except  in  the  case  of  lithia,  when  sulphuric  acid  is  sub- 
stituted for  the  hydrochloric  acid).  If  the  phosphoric  acid  is  to  be 
estimated  in  the  same  portion,  proceed  with  the  first  precipitate  (after 
washing  to  remove  the  larger  quantity  of  chloride),  according  to  b. 

(3.  (Only  applicable  in  the  case  of  fixed  alkalies.)  Separate  the  phos- 
phoric acid  as  phosphate  of  sesquioxide  of  iron,  according  to  one  of  the 
methods  given  § 134,  d , or  as  basic  phosphate  of  magnesia,  according  to 
§ 134,  e.  The  alkalies  are  contained  in  the  filtrate  as  nitrates  or  metal- 
lic chlorides. 

b.  From  Baryta , Strontia , Lim,e,  and  Oxide  of  Lead, 

The  compound  under  examination  is  dissolved  in  hydrochloric  or 
nitric  acid,  and  the  solution  precipitated  with  sulphuric  acid  in  slight 
excess.  In  the  separation  of  phosphoric  acid  from  strontia,  lime,  and 
oxide  of  lead,  alcohol  is  added  with  the  sulphuric  acid.  The  phosphoric 
acid  in  the  filtrate  is  determined  according  to  § 134,  5,  a (after  removal 
of  the  alcohol  by  evaporation).  The  determination  of  the  phosphoric 
acid  is  effected  most  accurately  by  saturating  the  fluid  with  carbonate 
of  soda,  evaporating  to  dryness,  and  fusing  the  residue  with  the  carbonates 
of  soda  and  potassa.  The  fused  mass  is  then  dissolved  in  water,  and  the 
further  process  conducted  as  in  § 134,  6,  a. 

c.  From  Magnesia  (see  also  d,  h , k ). 

The  phosphoric  acid  is  separated  as  in  § 134,  d,  a ; and  the  magnesia 
and  baryta  in  the  filtrate  are  separated  in  the  manner  described  § 154. 

d.  From  the  whole  of  the  Alkaline  Earths  and  fixedy  Alkalies  (comp. 

M)-  . 

a.  Dissolve  in  the  least  possible  quantity  of  nitric  acid,  add  a little 
chloride  of  ammonium,  precipitate  exactly  with  basic  acetate  of  lead,  pre- 
cipitate the  excess  of  lead  rapidly  from  the  filtrate  by  means  of  a little 
sulphuretted  hydrogen,  filter  and  determine  the  bases  in  the  filtrate. 
Besults  good. 

(3,  Dissolve  in  water,  and — in  the  case  of  alkaline  earthy  phosphates 


276 


DETERMINATION. 


[§  135. 


— the  least  possible  nitric  acid,  add  neutral  nitrate  of  silver  and  then 
carbonate  of  silver,  till  the  fluid  reacts  neutral.  All  phosphoric  acid 
now  separates  as  3 Ag  O,  P 05.  Warming  is  unnecessary.  Filter,  wash 
the  precipitate,  dissolve  it  in  dilute  nitric  acid,  precipitate  the  silver 
with  hydrochloric  acid,  and  determine  the  phosphoric  acid  in  the  filtrate 
according  to  § 134  6,  a.  The  filtrate  from  the  phosphate  of  silver  is 
freed  from  silver  by  hydrochloric  acid,  and  the  bases  are  then  deter- 
mined according  to  the  methods  already  given  (G.  Chancel*).  A 
good  and  convenient  method.  (If  the  substance  contains  alumina  or 
sesquioxide  of  iron,  these  bases  are  completely  precipitated  by  the  car- 
bonate of  silver,  and  are  found  mixed  with  the  phosphate  of  silver.) 

y.  Separate  the  phosphoric  acid  as  phosphate  of  sesquioxide  of  uranium 
(§  134,  c),  and  the  excess  of  sesquioxide  of  uranium  from  the  alkaline 
earths,  &c.,  in  the  filtrate,  according  to  § 161,  Supplement.  Results  good. 

8.  Separate  the  phosphoric  acid  according  to  § 134,  d,  j3  or  y.  The 
alkaline  earths  are  obtained  in  solution,  in  the  first  case,  as  metallic 
chlorides  together  with  alkaline  acetate  and  alkaline  metallic  chloride ; 
in  the  second  case  as  nitrates.  Results  good. 

e.  From  Alumina  (see  also  h and  k). 

a.  (Otto  and  Fresenius,  applicable  in  presence  of  sesquioxide  of 
iron.)  Dissolve  in  hydrochloric  or  nitric  acid,  dilute  a little,  add  a tol- 
erable quantity  of  tartaric  acid,  and  then  ammonia  in  excess.  If  you 
have  added  sufficient  tartaric  acid,  the  fluid  must  now  appeair  clear. 
Add  magnesia-mixture  in  slight  excess,  and  allow  to  stand  at  rest  for  24 
hours  in  a covered  vessel  without  warming,  then  filter,  and  wash  the 
precipitate  with  dilute  solution  of  ammonia ; to  free  it  completely  from 
alumina,  sesquioxide  of  iron,  and  basic  tartrate  of  magnesia,  redissolve 
it  in  hydrochloric  acid,  add  a very  little  tartaric  acid,  and  reprecipitate 
with  ammonia.  Treat  the  precipitate  now  as  directed  in  § 134,  b,  a.  To 
obtain  the  alumina  contained  in  the  filtrate,  add  some  nitrate  of  potassa 
and  a sufficient  quantity  of  carbonate  of  soda  to  effect  the  decomposition 
of  the  chloride  of  ammonium,  f evaporate  to  dryness,  and  ignite  the  resi- 
due in  a platinum  vessel.  Dissolve  in  nitric  or  hydrochloric  acid  by 
continued  application  of  heat,  and  separate  the  alumina  from  the  magne- 
sia as  directed  in  § 156.  This  method  is  only  to  be  recommended  when 
the  quantity  of  the  alumina,  of  the  sesquioxide  of  iron,  and  of  the  free 
acid  is  not  too  large,  since  [phosphate  of  magnesia  and  ammonia  is  con- 
siderably soluble  in  solutions  of  sesquisalts  of  iron  | and  alumina.  §]. 

3.  (Wackenroder  and  Fresenius.)  Precipitate  the  not  too  acid 
solution  with  ammonia,  taking  care  not  to  use  a great  excess  of  that 
reagent,  and  add  chloride  of  barium  as  long  as  a precipitate  continues 
to  form.  Digest  for  some  time,  and  then  filter.  The  precipitate  con- 
tains the  whole  of  the  alumina  and  the  whole  of  the  phosphoric  acid ; 
the  latter  combined  partly  with  alumina,  partly  with  baryta.  Filter  it 
off,  wash  it  a little,  and  dissolve  in  the  least  possible  quantity  of  hydro- 
chloric acid.  Warm,  saturate  the  solution  with  carbonate  of  baryta,  add 
pure  hydrate  of  potassa  in  excess,  apply  heat,  precipitate  the  baryta 

* Compt.  rend.  49,  997. 

f The  ignition  of  alumina  in  presence  of  chloride  of  ammonium  would  entail 
loss  by  the  escape  of  chloride  of  aluminium  (H.  Eose). 

[1;  Dick,  Memoirs  of  Geological  Surveys  of  Great  Britain,  1,  54. 1 

[§  Knapp,  Fres.  Zeitschrift,  iv.,  151.] 


§ 135.] 


PHOSPHORIC  ACID. 


277 


which  the  solution  may  contain  with  carbonate  of  soda,  and  filter.  You 
have  now  the  whole  of  the  alumina  in  the  solution,  the  whole  of  the 
phosphoric  acid  in  the  precipitate.  Acidify  the  solution  with  hydro- 
chloric acid,  boil  with  some  chlorate  of  potassa,  and  precipitate  as 
directed  § 105.  Dissolve  the  precipitate  in  hydrochloric  acid,  precipi- 
tate the  baryta  with  dilute  sulphuric  acid,  filter,  and  determine  the 
phosphoric  acid  in  the  filtrate  by  precipitation  with  solution  of  magne- 
sia in  the  manner  described  in  § 134,5,  a.  (Hermann  has  applied  a per- 
fectly similar  method  in  his  analysis  of  [impure]  gibbsite.) 

f From  Sesquioxide  of  Chromium  (see  also  h , X’). 

Fuse  with  carbonate  and  nitrate  of  soda,  and  separate  the  chromic 
acid  and  phosphoric  acid  in  the  manner  described  § 166. 

g.  From  the  Metallic  Oxides  of  the  Fourth  Group  (see  also  5,  k) . 

a.  Fuse  with  carbonate  of  soda.  Keep  in  fusion  for  some  time,  and  then 
boil  the  fused  mass  with  water.  Filter  and  wash  the  undissolved  residue. 
The  filtrate  contains  the  phosphoric  acid  combined  with  soda ; determine 
the  acid  as  directed  in  § 134,  5,  a.  Dissolve  the  residue,  which  generally 
retains  alkali,  in  acid,  and  determine  the  metal  by  the  appropriate  method. 

Should  a small  portion  of  manganic  acid  have  got  into  the  solution, 
this  is  removed  by  a little  sulphuretted  hydrogen  water. 

p.  Dissolve  in  hydrochloric  acid,  add  tartaric  acid,  chloride  of  ammo- 
nium, and  ammonia,  and  finally,  in  a flask  which  is  to  be  closed  after- 
wards, sulphide  of  ammonium,  put  the  flask  in  a moderately  warm  place, 
allowing  the  mixture  to  deposit  until  the  fluid  appears  of  a yellow  color, 
without  the  least  tint  of  green  ; filter,  and  determine  the  metals  as  di- 
rected in  §§  108  to  114.  The  phosphoric  acid  is  found  from  the  loss,  or 
determined  according  to  § 134,  b,  a.  The  magnesia-mixture  may  imme- 
diately be  added  to  the  filtrate,  which  contains  sulphide  of  ammonium. 
The  washed  precipitate  is  once  more  dissolved,  and  the  solution  repre- 
cipitated as  in  e,  a.  This  method  is  not  well  adapted  for  the  analysis 
of  the  phosphate  of  nickel. 

y.  (Special  method  for  effecting  the  separation  of  phosphoric  acid 
'from  the  oxides  of  iron.  it.  Arendt  and  W.  Knop  *).  Dissolve  in 
hydrochloric  acid  to  the  least  possible  volume  of  fluid,  add  to  the  clear 
solution  protocliloride  of  uranium  f,  until  the  color  inclines  distinctly  to 
green,  and  a drop  of  sulphocyanide  of  potassium  no  longer  produces  a 
red  tint  in  the  fluid.  Add  now  ammonia  to  distinct  alkaline  reaction, 
then  acetate  of  sesquioxide  of  uranium,  and  free  acetic  acid,  together 
with  a few  drops  of  solution  of  acetate  of  protoxide  of  uranium,  J and 

* Chem.  Centralbl.  1857,  182. 

4 Preparation  of  the  Protochloride  of  Uranium. — Dissolve  carbonate  of  sesqui- 
oxide of  uranium  and  ammonia  in  double  the  quantity  of  hydrochloric  acid  re- 
quired to  effect  solution,  add  a few  drops  of  solution  of  bichloride  of  platinum, 
and  throw  into  the  mixture  an  excess  of  fine  copper  turnings.  Heat,  and  let  the 
mixture  boil  from  10  to  15  minutes.  The  fluid  speedily  acquires  a green  color, 
and  the  conversion  of  chloride  to  subchloride  is  soon  effected.  To  separate  the 
dissolved  subchloride  of  copper,  let  the  mixture  boil  until  water  produces  a 
copious  precipitate  in  a sample  of  it.  When  this  point  is  attaint'd,  dilute  the  en- 
tire solution,  allow  it  to  cool,  filter  off  the  subchloride  of  copper,  transmit 
through  the  filtrate  sulphuretted  hydrogen  in  excess  ; filter  off  the  precipitated 
subsulphide  of  copper,  mix  the  solution  with  chloride  of  ammonium,  and  boil  un- 
til all  sulphuretted  hydrogen  has  escaped.  R.  Arendt  and  W.  Knop,  Chem.  Cen- 
tralbl., 1857,  164. 

X Preparation  of  Acetate  of  Protoxide  of  Uranium. — Precipitate  solution  of 


278 


DETERMINATION. 


L§  135. 


heat  to  boiling.  The  color  of  the  mixture  must  appear  distinctly  green- 
ish, and  not  dirty.  Let  the  solid  particles  completely  subside,  and  then 
decant  on  to  a filter  ; boil  the  precipitate  with  water  and  some  chloride 
of  ammonium,  and  decant  again.  Repeat  this  operation  once  more,  and 
then  treat  the  precipitate  as  directed  in  § 134,  c.  Separate  the  uranium 
and  iron  in  the  filtrate  as  directed  § 161,  Supplement.  The  results  are 
satisfactory.  The  addition  of  the  protochloride  of  uranium  has  for  its 
object  the  reduction  of  the  sesquichloride  of  iron  to  protochloride. 

S.  (Special  method  for  effecting  the  separation  of  phosphoric  acid  from 
the  oxides  of  iron,  Fresenius.)  Reduce  the  sesquioxide  of  iron  in  the 
solution,  if  necessary,  with  sulphite  of  soda,  add  pure  hydrate  of  potassa 
in  excess,  boil  until  the  precipitate  has  become  black  and  granular,  filter, 
and  wash  with  boiling  water.  The  precipitate  on  the  filter  is  protoses- 
quioxide  of  iron,  free  from  phosphoric  acid.  The  phosphoric  acid  in  the 
filtrate  is  determined  as  directed  in  § 134,  5,  a. 

h.  From  Metallic  Oxides  of  the  Second , Third , and  Fourth  Groups. 

More  especially  from  the  alkaline  earths,  alumina,  the  protoxides  of 

manganese,  nickel,  and  cobalt,  and  oxide  of  zinc ; also  from  sesquioxide 
of  iron,  if  the  quantity  of  the  latter  is  not  too  considerable. 

The  phosphoric  acid  is  precipitated  as  phosphate  of  binoxide  of  tin, 
according  to  the  directions  of  § 134,  b , y.  The  filtrate  contains  the 
bases  free  from  any  foreign  body  requiring  removal,  which,  of  course, 
greatly  facilitates  their  estimation. 

i.  From  the  Metcds  of  the  Fifth  and  Sixth  Groups. 

Dissolve  in  hydrochloric  or  nitric  acid,  precipitate  with  sulphuretted 
hydrogen,  filter,  determine  the  bases  by  the  methods  given  in  §§  115  to 
127,  and  the  phosphoric  acid  in  the  filtrate  by  the  method  described 
§ 134,  5,  a.  From  oxide  of  silver  the  phosphoric  acid  is  separated  in  a 
more  simple  way  still,  by  adding  hydrochloric  acid  to  the  nitric  acid  solu- 
tion ; from  oxide  of  lead  it  is  separated  most  readily  by  the  method  described 
in  b. 


h.  From  all  JBases  without  exception. 

Apply  Sonnenschein’s  method  (§  134,  5,  3),  and  in  the  filtrate  from 
the  phospho-molybdate  of  ammonia  separate  the  bases  from  the  molybdic 
acid.  As  molybdic  acid  comports  itself  with  sulphuretted  hydrogen 
and  sulphide  of  ammonium  like  a metal  of  the  sixth  group,  it  is  best  to 
precipitate  metals  of  the  sixth  and  also  of  the  fifth  group  from  acid 
solution  with  sulphuretted  hydrogen,  before  proceeding  to  precipitate  the 
phosphoric  acid  with  molybdic  acid  ; the  latter  will  then  have  to  be  sepa- 
rated only  from  the  metals  of  the  first  four  groups.  This  is  done  in  the 
following  manner  : mix  the  acid  fluid,  in  a flask,  with  ammonia  till  it 
acquires  an  alkaline  reaction,  add  sulphide  of  ammonium  in  sufficient 
excess,  close  the  mouth  of  the  flask,  and  digest  the  mixture.  As  soon  as 
the  solution  appears  of  a reddish-yellow  color,  without  the  least  tint  of 
green,  filter  off  the  fluid,  which  contains  sulphide  of  molybdenum  and 
ammonium,  wash  the  residue  with  water  mixed  with  some  sulphide  of 
ammonium,  and  separate  the  remaining  metallic  sulphides  and  hydrated 
oxides  of  the  fourth  and  third  groups  by  the  methods  which  will  be  foimd 
in  Section  Y.  Mix  the  filtrate  cautiously  with  hydrochloric  acid  in  mode- 


protochloride  of  uranium  with  ammonia,  and  dissolve  the  precipitate  in  acetic 
acid,  best  at  a high  temperature. 


BORACIC  ACID. 


279 


§ 136.1 


rate  excess,  remove  the  sulphide  of  molybdenum  according  to  the  directions 
of  § 128,  c,  and  determine  the  alkaline  earths  and  alkalies  in  the  filtrate. 

This  method  of  separating  the  phosphoric  acid  from  the  bases  is  highly 
to  be  recommended ; especially  in  cases  where  a small  quantity  of  phos- 
phoric acid  has  to  be  determined  in  presence  of  a very  large  quantity  of  ses- 
quioxide  of  iron  and  alumina,  as,  for  example,  in  iron  ores,  soils,  &c.  As 
arsenic  acid  and  silicic  acid  give,  with  molybdic  acid  and  ammonia,  similar 
yellow  precipitates,  it  is  necessary,  if  these  acids  are  present,  to  remove 
them  first.  However,  even  if  a little  silico-molybdate  of  ammonia  is  mixed 
with  the  phospho-molybdate,  the  estimation  of  the  phosphoric  acid  may 
yet  be  accurately  effected  (comp.  § 134,  b , ,3). 

As  the  separation  of  the  bases  from  the  large  excess  of  molybdic  acid 
used  is  somewhat  tedious,  the  best  way  is  to  arrange  matters  so  that  this 
process  may  be  altogether  dispensed  with.  Supposing,  for  instance,  you 
have  a fluid  containing  sesquioxide  of  iron,  alumina,  and  phosphoric  acid, 
estimate,  in  one  portion,  by  cautious  precipitation  with  ammonia,  the  total 
amount  of  the  three  bodies  ; in  another  portion  the  phosphoric  acid,  by 
means  of  molybdic  acid  ; and  in  a third,  the  sesquioxide  of  iron,  in  the 
volumetric  way.  The  difference  gives  the  alumina. 

§ 136. 

2.  Boracic  Acid. 

I.  Determination . 

The  determination  of  the  boracic  acid  in  an  aqueous  or  alcoholic  solution 
cannot  be  effected  by  simply  evaporating  the  fluid  and  weighing  the  residue, 
as  a notable  portion  of  the  acid  volatilizes  and  is  carried  off  with  the 
aqueous  or  alcoholic  vapor.  This  is  the  case  also  when  the  solution  is 
evaporated  with  oxide  of  lead  in  excess. 

Boracic  acid  is  estimated  either  indirectly  or  in  form  of  borojluoride 
of  potassium. 

1.  Indirect  Determination . 

a.  Mix  the  solution  of  the  boracic  acid  with  a weighed  quantity  of  pure 
carbonate  of  soda,*  in  amount  about  1^-  times  the  supposed  quantity  of  the 
boracic  acid  present.  Evaporate  the  mixture  to  dryness,  heat  the  residue 
to  fusion  and  weigh.  The  residue  contains  a known  amount  of  soda,  and 
unknown  quantities  of  carbonic  acid  and  boracic  acid.  Determine  the 
carbonic  acid  by  one  of  the  methods  given  in  § 139,  and  find  the  boracic 
acid  from  the  difference  (H.  Bose). 

b.  In  the  method  a , if  between  1 and  2 eq.  carbonate  of  soda  are  used  to 
1 eq.  boracic  acid — and  this  can  easily  be  done  if  one  knows  approximately 
the  amount  of  the  latter  present — all  the  carbonic  acid  is  expelled  by  the 
boracic  acid.  Hence  we  have  only  to  deduct  the  NaO  from  the  residue  to 
find  the  BO;3.  As  the  tumultuous  escape  of  carbonic  acid  may  lead  to 
loss,  it  is  well,  after  having  thoroughly  dried  the  residual  saline  mass, 
to  proj  ect  it  in  small  portions  cautiously  into  the  red  hot  crucible.  Besults 
good  (F.  Gr.  Schaffgotsch  f). 

c.  If  a solution  contains  alkalies  besides  boracic  acid,  the  latter  may  be 
determined,  according  to  C.  MARiGNAC,|in  the  following  manner: — Heu- 


* Fused  carbonate  of  soda  answers  the  purpose  best, 
f Pogg.  Ann.  107,  427.  X Zeitschrift  f.  analyt.  Chem.  1,  405. 


280 


DETERMINATION. 


[§  136. 

tralize  the  solution  with  hydrochloric  acid,  add  double  chloride  of  magne- 
sium and  ammonium  in  such  quantity  that  1 part  of  boracic  acid  may  have 
at  least  2 parts  of  magnesia,  then  add  ammonia  and  evaporate  to  dryness. 
If  a precipitate  is  formed  on  adding  the  ammonia  which  does  not  redissolve 
readily  on  warming,  add  more  chloride  of  ammonium.  The  evaporation 
is  conducted,  at  least  towards  the  end,  in  a platinum  dish,  a few  drops  of 
ammonia  being  added  from  time  to  time.  Ignite  the  dry  mass,  treat  with 
boiling  water,  collect  the  insoluble  precipitate  (consisting  of  borate  of 
magnesia  mixed  with  excess  of  magnesia)  on  a filter,  and  wash  with  boiling 
water  till  the  washings  remain  clear  with  nitrate  of  silver.  The  filtrate 
and  washings  are  mixed  with  ammonia,  evaporated  to  dryness,  ignited,  and 
washed  with  boiling  water  as  before. 

The  two  insoluble  residues  are  ignited  together  in  the  platinum  dish 
before  used,  as  strongly  as  possible,  and  for  a sufficiently  long  time,  in 
order  to  decompose  the  slight  traces  of  chloride  of  magnesium  that  might 
still  be  present.  After  weighing  determine  the  magnesia  and  find  the 
boracic  acid  from  the  difference.  The  estimation  of  the  magnesia  may  be 
made  by  dissolving  the  residue  in  hydrochloric  acid  and  precipitating  as 
phosphate  of  magnesia  and  ammonia,  or  more  quickly,  and  almost  as 
accurately,  by  dissolving  in  a known  quantity  of  standard  sulphuric  acid 
at  a boiling  temperature  and  determining  the  excess  of  acid  with  standard 
soda  (comp.  Alkalimetry). 

Should  a little  platinum  remain  behind  on  dissolving  the  residue,  it 
must  be  weighed  and  subtracted  from  the  weight  of  the  whole  (unless  the 
dish  was  weighed  first).  Results  satisfactory.  Marignac  obtained  in  two 
experiments  0*276  instead  of  0*280. 

2.  If  boracic  acid  is  to  be  determined  as  borojluoride  of  potassium.,  alka- 
lies oidy  (preferably  only  potash)  may  be  present.  The  process  is  conducted 
as  follows  : — Mix  the  fluid  with  pure  solution  of  potassa,  adding  for  each 
eq.  boracic  acid  supposed  to  be  present,  at  least  1 eq.  potassa  ; add  pure 
hydrofluoric  acid  (free  from  silicic  acid)  in  excess,  and  evaporate,  in  a 
platinum  dish,  on  the  water-bath,  to  dryness.  The  fumes  from  the  evapo- 
rating fluid  should  redden  litmus  paper,  otherwise  there  is  a deficiency  of 
hydrofluoric  acid.  The  residue  consists  now  of  K FI,  B Fl3  and  K FI, 
H FI.  Treat  the  dry  saline  mass,  at  the  common  temperature,  with  a 
solution  of  1 part  of  acetate  of  potassa  in  4 parts  of  water,  let  it  stand  a 
few  hours,  with  frequent  stirring,  then  decant  the  fluid  portion  on  to  a 
weighed  filter,  and  wash  the  precipitate  repeatedly  in  the  same  way, 
finally  on  the  filter,  with  solution  of  acetate  of  potassa,  until  the  last 
rinsings  are  no  longer  precipitated  by  chloride  of  calcium.  By  this  course 
of  proceeding  the  hydrofluate  of  fluoride  of  potassium  is  removed,  without 
a particle  of  the  borofluoride  of  potassium  being  dissolved.  To  remove 
the  acetate  of  potassa,  wash  the  precipitate  now  with  spirit  of  wine  of  0*85 
sp.  gr.,  dry  at  100°  and  weigh.  As  chloride  of  potassium,  nitrate  and 
phosphate  of  potassa,  salts  of  soda,  and  even,  though  with  some  difficulty, 
sulphate  of  potassa,  dissolve  in  solution  of  acetate  of  potassa,  the  presence 
of  these  salts  does  not  interfere  with  the  estimation  of  the  boracic  acid  ; 
however,  salts  of  soda  must  not  be  present  in  considerable  proportion,  as 
fluoride  of  sodium  dissolves  with  very  great  difficulty.  The  results  ob- 
tained by  this  method  are  satisfactory.  Stromeyer’s  experiments  gave 
from  97*5  to  100*7,  instead  of  100.  For  the  composition  and  properties 
of  borofluoride  of  potassium,  see  § 93,  5.  As  the  salt  is  very  likely  to 
contain  silicofiuoride  of  potassium  it  is  indispensable  to  test  it  for  that  sul> 


BORACIC  ACID. 


281 


§ 136.1 

stance ; tins  is  done  by  placing  a small  sample  of  it  on  moist  blue  litmus 
paper,  and  putting  another  sample  into  cold  concentrated  sulphuric  acid. 
If  the  blue  paper  turns  red,  and  effervescence  ensues  in  the  sulphuric  acid, 
the  salt  is  impure,  and  contains  silicofluoride  of  potassium.  To  remove 
this  impurity,  dissolve  the  remainder  of  the  salt,  after  weighing  it,  in 
boiling  water,  add  ammonia,  and  evaporate,  redissolve  in  boiling  water, 
add  ammonia,  &c.,  repeating  the  same  operation  at  least  six  times.  Finally, 
after  warming  once  more  with  ammonia,  filter  off  the  silicic  acid,  evaporate 
to  dryness,  and  treat  again  with  solution  of  acetate  of  potassa  and  alcohol 
(A.  Stromeyer*).  I was  obliged  to  modify  Stromeyer’s  method  for 
effecting  the  separation  of  the  silicic  acid,  the  results  of  my  experiments 
having  convinced  me  that  treating  the  salt  only  once  with  ammonia,  as 
recommended  by  that  chemist,  is  not  sufficient  to  effect  the  object  in  view. 

II.  Separation  of  Bor  acic  Acid  from  the  Bases. 

a.  From  the  Alkalies. 

Dissolve  a weighed  quantity  of  the  borate  in  water,  add  an  excess  of 
hydrochloric  acid,  and  evaporate  the  solution  on  the  water-bath.  To- 
wards the  end  of  the  operation  add  a few  more  drops  of  hydrochloric 
acid,  and  keep  the  residue  on  the  water-bath,  until  no  more  hydrochloric 
acid  vapors  escape.  Determine  now  the  chlorine  in  the  residue  (§  141), 
calculate  from  this  the  alkali,  and  you  will  find  the  boracic  acid  from  the 
difference. 

E.  Schweizer,  with  whom  this  methocToriginated,  states  that  it  gave 
him  very  satisfactory  results  in  the  analysis  of  borax.  It  will  answer 
also  for  the  estimation  of  the  bases  in  the  case  of  some  other  borates.  It 
is  self-evident  that  the  boracic  acid  may  be  estimated,  in  another  portion 
of  the  salt,  by  I.,  1,  c,  or  2.  If  you  have  to  estimate  boracic  acid  in 
presence  of  large  proportions  of  alkaline  salts,  make  the  fluid  alkaline 
with  potassa,  evaporate  to  dryness,  extract  the  residue  with  alcohol  and 
some  hydrochloric  acid,  add  solution  of  potassa  to  strongly  alkaline  re- 
action, distil  off  the  spirit  of  wine,  and  then  proceed  as  in  I.,  1,  c,  or  2 
(Aug.  Stromeyer,  loc.  cit.). 

h.  From  almost  all  other  Bases. 

The  compounds  are  decomposed  by  boiling  or  fusing  with  carbonate 
or  hydrate  of  potassa ; the  precipitated  base  is  filtered  off,  and  the  bora- 
cic acid  determined  in  the  filtrate,  according  to  the  directions  of  I.,  1,  c, 
or  2.  If  magnesia  was  present,  a little  of  this  is  very  likely  to  get  into 
the  filtrate,  and — if  process  I.,  2,  is  employed — upon  neutralizing  with 
hydrofluoric  acid,  this  separates  as  insoluble  fluoride  of  magnesium, 
which  may  either  be  filtered  off  at  once,  or  removed  subsequently,  by 
treating  the  boro-fluoride  of  potassium  with  boiling  water,  in  which  that 
salt  is  soluble,  and  the  fluoride  of  magnesium  insoluble. 

c.  From,  the  Metallic  Oxides  of  the  Fourth , Fifth  and  Sixth  Groups. 

The  metallic  oxides  are  precipitated  by  sulphuretted  hydrogen,  or,  as 
the  case  may  be,  sulphide  of  ammonium,  and  determined  by  the  appro- 
priate methods.  The  quantity  of  boracic  acid  may  often  be  inferred 
from  the  loss.  If  it  has  to  be  estimated  in  the  direct  way,  the  filtrate, 
after  addition  of  solution  of  potassa  and  some  nitrate  of  potassa,  is  eva- 


* Anna!,  d.  Chem.  u.  Pkarm.  100,  82. 


232 


DETERMINATION. 


porated  to  dryness,  the  residue  ignited,  and  the  boracic  acid  estimated  by 
I.,  1 c,  or  2.  In  cases  where  the  metal  has  been  precipitated  by  sul- 
phuretted hydrogen  from  acid  or  neutral  solutions,  the  boracic  acid  may 
also  be  determined  in  the  filtrate — in  the  absence  of  other  acids — by 
I.,  1 a or  b,  after  the  complete  removal  of  the  sulphuretted  hydrogen 
by  transmitting  carbonic  acid  through  the  fluid. 

d.  From  the  whole  of  the  Fixed  Bases. 

A portion  of  the  very  finely  pulverized  compound  under  examination 
is  weighed,  put  into  a capacious  platinum  dish,  and  digested  with  a suf- 
ficient quantity  of  hydrofluoric  acid  ; pure  concentrated  sulphuric  acid  is 
then  gradually  added,  drop  by  drop,  and  the  mixture  heated,  gently  at 
first,  then  more  strongly,  until  the  excess  of  the  sulphuric  acid  is  com- 
pletely expelled.  In  this  operation  the  boracic  acid  goes  off  in  the  form 
of  fluoride  of  boron  (B  03  + 3 H FI— B Fl3  + 3 H O).  The  residue  con- 
tains the  bases  in  the  form  of  sulphates ; the  bases  are  determined  by 
the  appropriate  methods,  and  the  quantity  of  the  boracic  acid  is  inferred 
from  the  difference  between  the  weight  of  the  separated  base  and  that  of 
the  analyzed  borate.  The  application  of  this  method  presupposes,  of 
course,  that  the  analyzed  compound  is  decomposable  by  sulphuric  acid. 

§ 137. 

3.  Oxalic  Acid. 

I.  Determination . 

Oxalic  acid  is  either  precipitated  as  oxalate  of  lime , and  the  latter 
determined  as  carbonate  of  lim,e  / or  the  amount  contained  in  a com- 
pound is  inferred  from  the  quantity  of  solution  of  permanganate  of 
potassa  required  to  effect  the  conversion  into  carbonic  acid  ; or  from  the 
quantity  of  gold  which  it  reduces ; or  from  the  amount  of  carbonic  acid 
which  it  yields  upon  accession  of  1 eq.  oxygen. 

a.  Determination  as  Carbonate  of  Lime . 

Precipitate  with  solution  of  acetate  of  lime,  added  in  moderate  excess, 
and  treat  the  precipitated  oxalate  of  lime  as  directed  in  § 103.  If  this 
method  is  to  yield  accurate  results,  the  solution  must  be  neutral  or  slightly 
acid  with  acetic  acid  / it  must  not  contain  alumina,  sesquioxide  of  chro- 
mium, or  oxides  of  the  heavy  metals,  more  especially  sesquioxide  of  iron 
or  oxide  of  copper ; therefore,  where  these  conditions  do  not  exist,  they 
must  first  be  supplied. 

b.  Determination  by  means  of  Solution  of  Permanganate  of  Potassa. 

Determine  the  strength  of  the  solution  of  permanganate  of  potassa,  as 

directed  p.  196,  cc,  by  means  of  oxalic  acid  ; then  dissolve  the  compound 
in  which  the  oxalic  acid  is  to  be  estimated,  and  which  must  be  free  from 
all  other  bodies  that  might  act  on  solution  of  permanganate  of  potassa, 
in  400  or  500  parts  of  water,  or,  as  the  case  may  be,  acid  and  water ; 
add,  if  necessary,  a further,  not  too  small,  quantity  of  sulphuric  acid, 
heat  to  about  60°,  and  then  add  the  permanganate,  drop  by  drop,  with 
constant  stirring,  until  the  fluid  just  shows  a red  tint  (compare  p.  196). 
Knowing  the  quantity  of  oxalic  acid  which  100  c.  c.  of  the  standard  per- 
manganate will  oxidize,  a simple  calculation  will  give  the  quantity  of 
oxalic  acid  corresponding  to  the  c.  c.  of  permanganate  used  in  the  ex- 
periment. The  results  are  very  accurate. 


OXALIC  ACID. 


283 


§ 137.] 

c.  Determination  from  the  reduced  Gold  (H.Rose). 

a.  In  Compounds  soluble  in  Water. 

Add  to  the  solution  of  the  oxalic  acid  or  the  oxalate  a solution  of 
sodio-terchloride,  or  ammonio-terchloride  of  gold,  and  digest  for  some 
time  at  a temperature  near  ebullition,  with  exclusion  of  direct  sunlight. 
Collect  the  precipitated  gold  on  a filter,  wash,  dry,  ignite,  and  weigh. 
1 eq.  gold  (196)  corresponds  to  3 eq.  C2  03  (3x36=108). 

|3.  In  Compounds  insoluble  in  Water. 

Dissolve  in  the  least  possible  amount  of  hydrochloric  acid,  dilute 
with  a very  large  quantity  of  water,  in  a capacious  flask,  cleaned  pre- 
viously with  solution  of  soda ; add  solution  of  gold  in  excess,  boil  the 
mixture  some  time,  let  the  gold  subside,  taking  care  to  exclude  sunlight, 
and  proceed  as  in  a. 

d.  Determination  as  Carbonic  Acid. 

This  may  be  effected  either, 

a.  By  the  method  of  organic  analysis  (§  174) ; or, 

|3.  By  mixing  the  oxalic  acid  or  oxalate  with  finely  pulverized  binox- 
ide  of  manganese  in  excess,  and  adding  sulphuric  acid  to  the  mixture,  in 
an  apparatus  so  constructed  that  the  disengaged  carbonic  acid  passes  off 
perfectly  dry. 

The  theory  of  this  method  may  be  illustrated  by  the  following  equa- 
tion : 

C2  03+Mn  02+S  03=Mn  O,  S 03  + 2 C O, 

For  each  1 eq.  oxalic  acid  we  obtain  accordingly  2 eq.  carbonic  acid. 
For  the  apparatus  and  process,  I refer  to  the  chapter  on  the  examination 
of  manganese  ores,  in  the  special  part  of  this  work.  Here  I may  remark 
that  free  oxalic  acid  must  first  be  prepared  for  the  process  by  slight 
supersaturation  with  ammonia,  and  also  that  9 parts  of  anhydrous  ox- 
alic acid  require  theoretically  1 1 parts  of  (pure)  binoxide  of  manganese. 
Since  an  excess  of  the  latter  substance  does  not  interfere  with  the  accu- 
racy of  the  results,  it  is  easy  to  find  the  amount  to  be  added.  The 
binoxide  of  manganese  need  not  be  pure,  but  it  must  contain  no  carbon- 
ate. This  method  is  expeditious,  and  gives  very  accurate  results,  if 
the  process  is  conducted  in  an  apparatus  sufficiently  light  to  admit  of 
the  use  of  a delicate  balance. 

Instead  of  binoxide  of  manganese,  chromate  of  potassa  may  be  used ; 
(compare  § 130,  c .) 

II.  Separation  of  Oxalic  Acid  from  the  Dases. 

The  most  convenient  way  of  analyzing  oxalates  is,  in  all  cases,  to 
determine  in  one  portion,  the  acid,  by  one  of  the  methods  given  in  I.,  in 
another  portion,  the  base,  particularly  as  the  latter  object  may  be  gene- 
rally effected  by  simple  ignition  in  the  air,  which  reduces  the  salt  either 
to  the  metallic  state  {e.  g.f  oxalate  of  silver),  or  to  pure  oxide  (e.  g.  oxa- 
late of  lead),  or  to  carbonate  ( e . g .,  the  oxalates  of  the  alkalies  and  alka- 
line earths.) 

If  acid  and  base  have  to  be  determined  in  one  and  the  same  portion 
of  the  oxalate,  the  following  methods  may  be  resorted  to : 

a.  The  oxalic  acid  is  determined  by  I.,  c,  and  the  gold  separated  from 
the  bases  in  the  filtrate  by  the  methods  given  in  Section  Y. 


284 


DETERMINATION-. 


b.  In  many  soluble  salts  the  oxalic  acid  may  be  determined  by  the 
method  I.,  a\  separating  the  bases  afterwards  from  the  excess  of  the 
salt  of  lime  by  the  methods  given  in  Section  V. 

c.  Many  oxalates  whose  bases  are  precipitated  by  carbonate  of  potassa 
or  carbonate  of  soda,  and  are  insoluble  in  an  excess  of  the  precipitant, 
may  be  decomposed  by  boiling  with  an  excess  of  solution  of  carbonate 
of  potassa  or  carbonate  of  soda,  oxide  or  carbonate  being  formed  on  the 
one,  and  alkaline  oxalate  on  the  other  side. 

d.  All  salts  of  oxalic  acid  with  the  oxides  of  the  fourth,  fifth,  and 
sixth  groups,  may  be  decomposed  with  sulphuretted  hydrogen,  or  sul- 
phide of  ammonium. 

§ 138. 

4.  Hydrofluoric  Acid. 

I.  Determination. 

Free  hydrofluoric  acid  in  aqueous  solution  is  best  determined  as 
Jiuoride  of  calcium.  For  this  purpose,  carbonate  of  soda  is  added 
in  moderate  excess,  then  a solution  of  chloride  of  calcium  as  long  as  a 
precipitate  continues  to  form  ; when  the  precipitate,  which  consists  of 
fluoride  of  calcium  and  carbonate  of  lime,  has  subsided,  it  is  washed,  first 
by  decantation,  afterwards  on  the  filter,  and  dried ; when  dry,  it  is  ignited 
in  a platinum  crucible  (§  53)  ; water  is  then  poured  over  it,  in  a platinum 
or  porcelain  dish,  acetic  acid  added  in  slight  excess,  the  mixture  evaporated 
to  dryness  on  the  water-bath,  and  heated  on  the  latter  until  all  odor  of 
acetic  acid  disappears.  The  residue,  which  consists  of  fluoride  of  calcium 
and  acetate  of  lime,  is  heated  with  water,  the  fluoride  of  calcium  filtered 
off,  washed,  dried,  ignited  (§  53),  and  weighed.  If  the  precipitate  of 
fluoride  of  calcium  and  carbonate  of  lime  were  treated  with  acetic  acid, 
without  previous  ignition,  the  washing  of  the  fluoride  would  prove  a 
difficult  operation.  Presence  of  nitric  or  hydrochloric  acid  in  the  aque- 
ous solution  of  the  hydrofluoric  acid  does  not  interfere  with  the  process 
(H.  Rose). 

II.  Separation  of  F luorine  from  the  Metals, 
a.  Soluble  Fluorides. 

If  the  solutions  have  an  acid  reaction,  carbonate  of  soda  is  added  in 
excess.  If  this  produces  no  precipitate,  the  fluorine  is  determined  by 
the  method  given  in  I.,  and  the  bases  in  the  filtrate  are  separated  from 
the  excess  of  lime,  and  from  the  soda,  by  the  methods  given  in  Section 
V.  But  if  the  carbonate  of  soda  produces  a precipitate,  the  mixture  is 
heated  to  boiling,  then  filtered,  and  the  fluorine  determined  in  the  fil- 
trate by  the  method  given  in  I. ; the  base  is  in  the  residue,  which  must, 
however,  first  be  tested,  to  make  sure  that  it  contains  no  fluorine.  Neu- 
tral solutions  are  mixed  with  a sufficient  quantity  of  chloride  of  calcium, 
and  the  mixture  heated  to  boiling  in  a platinum  dish,  or,  but  less  ap- 
propriately, in  a porcelain  dish ; the  precipitate  of  fluoride  of  calcium  is 
allowed  to  subside,  thoroughly  washed  with  hot  water  by  decantation, 
transferred  to  the  filter,  dried,  ignited,  and  weighed.  The  bases  in  the 
filtrate  are  then  separated  from  the  excess  of  the  salt  of  lime  by  the 
usual  methods.  That  the  bases  may  be  determined  also  in  separate  por- 
tions by  the  methods  given  in  b,  need  hardly  be  stated. 


CARBONIC  ACID. 


285 


§ 139.] 


b.  Insoluble  Fluorides . 

a.  Anhydrous  insoluble  Fluorides. 

The  finely  pulverized  and  accurately  weighed  substance  is  heated  for 
some  time  with  pure  concentrated  sulphuric  acid,  and  finally  ignited  until 
the  free  sulphuric  acid  is  completely  expelled.  The  residuary  sulphate  is 
weighed,  and  the  metal  contained  in  it  calculated.  The  difference  between 
the  calculated  weight  of  the  metal  and  that  of  the  original  fluoride  shows 
the  amount  of  fluorine  originally  present  in  the  analyzed  compound.  In 
cases  where  we  have  to  deal  with  a metal  whose  sulphate  gives  off  part  of 
the  sulphuric  acid  upon  ignition,  or  where  the  residue  contains  several 
metals,  it  is  necessary  to  subject  the  residue  to  analysis  before  this  cal- 
culation can  be  made. 

f3.  Hydrated  insoluble  Fluorides. 

A sample  of  the  compound  under  examination  is  heated  in  a tube. 

aa.  The  Water  expelled  does  not  redden  Litmus  Paper. 

In  this  case  the  amount  of  water  present  is  ascertained  by  igniting  the 
hydrated  compound,  and  the  fluorine  and  metal  are  subsequently  deter- 
mined as  directed  in  II.,  b.  a. 

bb.  The  Water  expelled  has  an  acid  reaction. 

The  fluoride  under  examination  is,  in  the  first  place,  treated  with  sul- 
phuric acid,  as  directed  in  IT.,  b , a,  to  determine  the  metal  on  the  one  hand, 
and  the  water  -f-  fluorine  on  the  other.  Another  weighed  portion  is  then 
mixed,  in  a small  retort,  with  about  6 parts  of  recently  ignited  oxide  of 
lead  ; the  mixture  is  covered  with  a layer  of  oxide  of  lead,  the  retort 
weighed,  and  the  water  expelled  by  the  application  of  heat,  increased 
gradually  to  redness.  No  hydrofluoric  acid  escapes  in  this  process.  The 
■weight  of  the  expelled  water  is  inferred  from  the  loss.  The  first  operation 
having  given  us  the  water  + fluorine,  and  the  second,  the  water  alone,  the 
difference  is  consequently  the  fluorine. 

In  the  fifth  section  we  shall  have  occasion  to  speak  of  another  method  of 
determining  fluorine  (in  the  chapter  on  the  separation  of  fluorine  from 
silicic  acid). 

Fourth  Division  of  the  First  Group  of  the  Acids . 

Carbonic  Acid — Silicic  Acid. 


§ 139. 

1.  Carbonic  Acid. 

I.  Determination, 
a.  In  a mixture  of  Gases. 

After  thoroughly  drying  the  gases  with  a ball  of  chloride  of  calcium, 
measure  them  accurately,  in  a graduated  tube  over  mercury,  insert  a 
moistened  ball  of  hydrate  of  potassa,  cast  on  a platinum  wire  in  a pistol 
bullet-mould,  and  leave  this  in  the  tube  for  24  hours,  or  until  the  volume 
of  the  gas  ceases  to  show  further  diminution  ; withdraw  the  ball,  and 
measure  the  gas  remaining,  re-insert  the  same  or  a fresh  moistened  ball  of 
potassa  and  repeat  till  no  further  absorption  takes  place.  The  carbonic 
acid  gas  is  inferred  from  the  difference,  provided  the  gaseous  mixture  con- 
tained no  other  gas  liable  to  absorption  by  potassa  (compare  §§  12-16). 


286 


DETERMINATION. 


[§  139. 


If  the  amount  of  carbonic  acid  is  very  small,  this  process  does  not  yield 
sufficiently  accurate  results.  In  such  cases  one  of  the  methods  recom- 
mended for  the  estimation  of  carbonic  acid  in  atmospheric  air  (see  § 241) 
should  be  employed. 

b.  In  Aqueous  Solution, 
a.  With  Hydrate  of  Lime. 

Into  a flask,  holding  about  300  c.  c.  and  provided  with  a good  india- 
rubber  cork,  put  2 to  3 grm.  hydrate  of  lime  perfectly  free  from  carbon- 
ate,* tare  or  weigh  exactly,  add  the  carbonic  acid  water,  cork  immedi- 
ately and  weigh  again.  (If  the  water  is  measured  with  a plunging 
syphon,  of  course  this  mode  of  ascertaining  the  amount  of  water  em- 
ployed is  superfluous.)  Heat  the  contents  of  the  flask  for  some  time 
in  a water-bath  (raising  the  cork  every  now  and  then)  to  hasten  the  con- 
version of  the  amorphous  carbonate  of  lime  into  the  crystalline,  and 
pour  off  the  clear  fluid  as  completely  as  possible  without  disturbing  the 
precipitate  through  a small  ribbed  filter.  This  operation  is  soon  fin- 
ished, and  the  filter  is  at  once — without  washing — thrown  into  the  flask 
containing  the  precipitate  and  the  rest  of  the  fluid ; the  carbonic  acid  is 
determined  now  according  to  II.,  e ; or,  if  the  carbonic  acid  water  con- 
tains bicarbonate  of  an  alkali,  it  is  well  to  add,  besides  the  hydrate  of 
lime,  also  enough  chloride  of  calcium  to  decompose  the  alkaline  car- 
bonate. 

(5.  After  Pettenkofer.  f 

The  principle  of  this  simple  and  expeditious  process  consists  in 
mixing  the  carbonic  acid  water  with  a measured  quantity  of  standard 
lime-water  (or,  under  certain  circumstances,  baryta  water)  in  excess. 
After  complete  separation  of  the  carbonate  of  lime  the  excess  of  alkaline 
earth  in  the  fluid  is  determined  in  an  aliquot  part  by  means  of  stand- 
ard solution  of  oxalic  acid  ; the  difference  gives  the  lime  precipitated  by 
the  carbonic  acid,  and  consequently  the  amount  of  the  latter  present. 

If  a water  contains  only  free  carbonic  acid,  the  analyst  has  only  to 
bear  in  mind  that  the  carbonate  of  lime  formed  is  at  first,  as  long  as  it 
remains  amorphous,  very  perceptibly  soluble  in  water,  to  which  it  com- 
municates an  alkaline  reaction.  Hence  the  unprecipitated  lime  in  the 
fluid  cannot  be  estimated  till  the  carbonate  of  lime  has  separated  in  the 
crystalline  form — this  takes  8 or  10  hours  if  the  mixture  is  not  warmed 
to  70°  or  80°. 

If,  on  the  contrary,  a water  contains  an  alkaline  carbonate  or  any 
other  alkaline  salt  whose  acid  would  be  precipitated  by  lime,  a neutral 
solution  of  chloride  of  calcium  must  first  be  added  to  decompose  the 
same.  This  addition,  too,  prevents  any  inconvenience  arising  from  the 
presence  of  free  alkali  in  the  lime-water  or  of  carbonate  of  magnesia  in 
the  carbonic  acid  water ; this  inconvenience  consists  in  the  fact  that 
oxalate  of  an  alkali  or  of  magnesia  enters  into  double  decomposition 
with  carbonate  of  lime  (which  is  never  entirely  absent  from  the  fluid  to 

* This  is  prepared  by  slaking  freshly  burnt  lime  with  water  in  such  a manner 
that  the  hydrate  obtained  appears  dry  and  pulverulent.  Should  it  contain  carbonic 
acid  (as  may  be  seen  by  putting  a portion  into  hydrochloric  acid)  it  is  ignited  in 
a current  of  air  free  from  carbonic  acid  in  a tube  of  difficultly  fusible  glass  placed 
in  a combustion  furnace. 

f Buchner’s  neues  Repert.  10,  1. 


CARBONIC  ACID. 


§ 139.] 


28  7 


be  analyzed),  forming  oxalate  of  lime  and  carbonate  of  the  alkali  or  of 
magnesia,  which  latter  will  of  course  again  take  up  oxalic  acid. 

In  the  presence  of  magnesia  salts  in  carbonic  acid  water,  in  order  to 
avoid  the  precipitation  of  the  magnesia,  a little  chloride  of  ammonium 
must  also  be  added,  but  in  this  case  heat  must  not  be  applied  to  induce 
the  carbonate  of  lime  to  become  more  quickly  crystalline,  as  ammonia 
would  be  thereby  expelled. 

In  making  the  determination,  the  first  thing  to  be  done  is  to  ascertain 
the  relation  between  the  lime  water  and  a standard  solution  of  oxalic 
acid.  Pettenkofer  makes  the  latter  solution  by  dissolving  2’8636 
grm.  pure  unefiloresced  dry  cr}Tstallized  oxalic  acid  to  1 litre ; 1 c.  c.  of 
this  is  equivalent  to  1 mgrm.  carbonic  acid.  The  lime  water  is  stand- 
ardized as  follows : measure  45  c.  c.  into  a little  flask  which  can  be 
closed  by  the  thumb,  and  then  run  in  from  the  burette  the  solution  of 
oxalic  acid  till  the  alkaline  reaction  has  just  vanished.  During  the 
operation  the  flask  is  closed  with  the  thumb  and  gently  shaken.  The 
end  is  attained  as  soon  as  a drop  taken  out  with  a glass  rod  and  applied 
to  delicate  turmeric  paper  produces  no  brown  ring.  The  first  experiment 
is  a rough  one,  the  second  should  be  exact. 

The  analysis  of  a carbonic  acid  water  (a  spring  water,  for  instance)  is 
performed  by  transferring  100  c.  c.  to  a dry  flask,  adding  3 c.  c.  of  a 
neutral  and  nearly  saturated  solution  of  chloride  of  calcium  and  2 c.  c.  of 
a saturated  solution  of  chloride  of  ammonium,  then  45  c.  c.  of  the  stand- 
ard lime  water  ; close  the  flask  with  an  india-rubber  cork,  shake  and  allow 
to  stand  12  hours.  The  fluid  contents  of  the  flask  measure  consequently  150 
c.  c.  From  the  clear  fluid  take  out  by  means  of  a pipette  two  portions 
of  50  c.  c.  each,  and  determine  the  free  lime  by  means  of  oxalic  acid,  in 
the  first  portion  approximately,  in  the  second  exactly.  Multiply  the 
c.  c.  used  in  the  last  experiment  by  3 and  deduct  the  product  from  the 
c.  c.  of  oxalic  acid  which  correspond  to  45  c.  c.  of  lime  water.  The  dif- 
ference shows  the  lime  precipitated  by  carbonic  acid;  each  c.  c.  corre- 
sponds to  1 mgrm.  carbonic  acid. 

The  method  is  convenient  and  good ; it  is  especially  to  be  recom- 
mended for  dilute  carbonic  acid  water.  In  water  containing  much  car- 
bonic acid  it  is  well  to  replace  the  lime-  by  baryta  water ; compare  the 
determination  of  carbonic  acid  in  atmospheric  air,  § 241. 


II.  Separation  of  Carbonic  Acid  from  the  Bases , and  its 
Estimation  in  Carbonates. 

a.  Separation  from  Neutral  Carbonates  of  Alkalies  and  the  Alkaline 

Earths. 

If  the  salts  contain  unquestionably  1 eq.  carbonic  acid  to  1 eq.  base, 
and  there  is  no  other  salt  with  alkaline  reaction  present,  we  may  deter- 
mine the  quantity  of  the  base  by  the  alkalimetric  method  (§§  207, 
208,  201),  and  calculate  for  each  1 eq.  base  1 eq.  carbonic  acid. 

b.  Separation  from  Eases  vnhich  upon  Ignition  readily  and  completely 

yield  the  Carbonic  Acid  with  which  they  are  combined. 

Such  are,  for  instance,  the  carbonates  of  zinc,  cadmium,  lead,  copper, 
magnesia,  &c. 

a.  Anhydrous  Carbonates. 

Ignite  the  weighed  substance  in  a platinum  crucible  (carbonates  of 


288 


DETERMINATION. 


[§  139. 

cadmium  and  lead  in  a porcelain  crucible),  until  the  weight  of  the  residue 
remains  constant.  The  results  are,  of  course,  very  accurate.  Substances 
liable  to  absorb  oxygen  upon  ignition  in  the  air  are  ignited  in  a bulb- 
tube,  through  which  a stream  of  dry  carbonic  acid  gas  is  conducted.  The 
carbonic  acid  is  inferred  from  the  loss. 

3.  Hydrated  Carbonates. 

The  substance  is  ignited  in  a bulb-tube  through  which  dried  air,  or, 
in  presence  of  oxidizable  substances,  carbonic  acid  is  transmitted,  and 
which  is  connected  with  a chloride  of  calcium  tube,  by  means  of  a dry, 
close-fitting  cork.  During  the  ignition,  the  posterior  end  of  the  bulb- 
tube  is,  by  means  of  a small  lamp,  kept  sufficiently  hot  to  prevent  the 
condensation  of  water  in  it,  care  being  taken,  however,  to  guard  against 
burning  the  cork.  The  loss  of  weight  of  the  tube  gives  the  amount  of 
the  water -(-the  carbonic  acid  ; the  increase  of  weight  gained  by  the 
chloride  of  calcium  tube  gives  the  amount  of  the  water,  and  the  differ- 
ence accordingly  that  of  the  carbonic  acid.  A somewhat  wide  glass  tube 
may  also  be  put  in  the  place  of  the  bulb-tube,  and  the  substance  intro- 
duced into  it  in  a little  boat,  which  is  weighed  before  and  after  the 
operation. 

c.  Separation  from  all  Bases , without  exception , in  Anhydrous  Carbo- 

nates. 

Fuse  vitrified  borax  in  a weighed  platinum  crucible,  allow  to  cool  in 
the  desiccator,  weigh,  then  transfer  the  well-dried  substance  to  the  crucible 
and  weigh  again.  The  weights  of  both  carbonate  and  borax  are  thus 
ascertained.  They  should  be  in  about  the  proportion  of  1:4.  Heat  is 
then  applied,  which  is  gradually  increased  to  redness,  and  maintained  at 
this  temperature  until  the  contents  of  the  crucible  are  in  a state  of  calm 
fusion.  The  crucible  is  now  allowed  to  cool,  and  weighed.  The  loss  of 
weight  is  carbonic  acid.  The  results  are  very  accurate  (Schaffgotsch). 

I must  add  that  borax-glass  may  be  kept  in  a state  of  fusion  at  a red 
heat  for  \ to  an  hour  without  the  occurrence  of  any  volatilization,  but 
that  at  a white  heat  (by  igniting  over  the  gas-bellows),  even  in  a few 
minutes,  it  suffers  a decided  loss.*  A few  bubbles  of  carbonic  acid 
remaining  in  the  fusing  mass  are  without  any  influence  on  the  result. 

d.  Separation  from  all  Bases  loithout  exception. 

( Estimation  of  the  Acid  from  the  loss  of  weight.) 

aa.  Carbonates  whose  Bases  form  Soluble  Salts  with  Sulphuric  Acid. 

The  process  is  conducted  in  the  apparatus  illustrated  by  fig.  53. 

The  size  of  the  flasks  depends  upon  the  capacity  of  the  balance  which 
the  operator  possesses.  The  tube  a is  closed  at  b by  means  of  a small 
wax  stopper ; f the  other  end  of  the  tube  a is  open,  as  are  also  both  ends 
of  c and  d.  The  flask  B is  nearly  half  filled  with  concentrated  sulphuric 
acid  ; the  tubes  must  fit  air-tight  in  the  perforations  of  the  corks,  and  the 
latter  equally  so  in  the  mouths  of  the  flasks.  The  weighed  substance 
is  put  into  A ; this  flask  is  then  filled  about  one-third  with  water,  the 
cork  properly  inserted,  and  the  apparatus  tared  on  the  balance. 


* Zeitschrift  f.  analyt.  Chem.  1,  65. 

f Or  with  a small  piece  of  india-rubber  tube,  drawn  over  it,  and  having  inserted 
in  the  other  end  a short  piece  of  glass  rod. 


§ 139.] 


CARBONIC  ACID. 


289 


A few  bubbles  of  air  are  now  sucked  out  of  d}  by  means  of  a small  india- 
rubber  tube.  This  serves  to  rarefy  the  air  in  A also,  and  causes  the  sul- 
phuric acid  in  B to  ascend  in  the  tube  c.  The  latter  is  watched  for  some 
time,  to  ascertain  whether  the  column  of  sulphuric  acid  in  it  remains 
stationary,  which  is  a proof  that  the  apparatus  is  air-tight.  Air  is  then 
again  sucked  out  of  d , which  causes  a por- 
tion of  the  sulphuric  acid  to  flow  over  into 
A.  The  carbonate  in  the  latter  flask  is 
decomposed  by  the  sulphuric  acid,  and 
the  liberated  carbonic  acid,  completely 
dried  in  its  passage  through  the  concen- 
trated sulphuric  acid  in  B,  escapes 
through  d.  When  the  evolution  of  the 
gas  slackens  a fresh  portion  of  sulphuric 
acid  is  made  to  pass  over  into  A , by  re- 
newed suction  through  d ’ and  the  same 
operation  is  repeated  until  the  whole  of 
the  carbonate  is  decomposed.  A more 
vigorous  suction  is  now  applied,  to  make 
a larger  amount  of  sulphuric  acid  pass 
over  into  A , whereby  the  contents  of  that 
flask  are  considerably  heated ; when  the 
evolution  of  gas  bubbles  has  completely  Fig-.  53. 

ceased,  the  wax  stopper  on  a is  opened, 

or  the  glass  rod  removed  from  the  india-rubber  cap,  and  suction  applied 
to  g?,  until  the  air  sucked  out  tastes  no  longer  of  carbonic  acid.* 

After  about  3 hours,  the  apparatus  is  replaced  upon  the  balance,  and 
the  equilibrium  restored  by  additional  weights.  The  sum  of  the  weights 
so  added  indicates  the  amount  of  carbonic  acid  originally  present  in  the 
substance. 

[f  the  flasks  A and  B are  selected  of  small  size,  the  apparatus  may  be 
so  constructed  that,  together  with  the  contents,  it  need  not  weigh  above 
seventy  grammes,  admitting  thus  of  being  weighed  on  a delicate  balance. 
The  results  obtained  by  the  use  of  this  apparatus,  first  suggested  by  W ill 
and  myself,  are  very  accurate,  provided  the  quantity  of  the  carbonic 
acid  be  not  too  trifling.  Manifold  modifications  of  the  apparatus  have 
been  proposed,  principally  in  order  to  make  it  lighter.  See  Geissler’s 
Apparatus,  p.  291. 

If  sulphites  or  sulphides  are  present,  together  with  the  carbonates,  their 
injurious  influence  is  best  obviated  by  adding  to  the  carbonate  solution  of 
yellow  chromate  of  potassa  in  more  than  sufficient  quantity  to  effect  their 
oxidation.  If  chlorides  are  present,  in  order  to  prevent  the  evolution  of 
hydrochloric  acid,  add  to  the  evolution  flask  a sufficient  quantity  of  sul- 
phate of  silver  in  solution,  or  connect  the  exit  tube  d with  a small  prepared 
U-tube,  which  is,  of  course,  first  tared  with  the  apparatus,  and  afterwards 
weighed  with  it.  This  U-tube  is  prepared — in  accordance  with  the  happy 
proposal  of  Stolba — by  filling  with  fragments  of  pumice  which  have  been 
boiled  with  an  excess  of  concentrated  solution  of  sulphate  of  copper,  till 
the  air  has  been  expelled,  and  then  dried  and  heated  to  complete  dehy- 
dration of  the  copper  salt.  If  the  U-tube  is  only  8 cm.  high  and  has 
an  internal  diameter  of  1 cm.,  it  answers  the  purpose  very  well.  The 

* In  accurate  experiments,  it  is  advisable  to  connect  the  end  b of  the  tube  a 
with  a chloride  of  calcium  tube  during  the  process  of  suction. 

19 


290 


DETERMINATION. 


end  not  connected  with  d is  provided  with  a perforated  cork  and  short 
glass  tube.  We  apply  suction  to  this  by  means  of  a flexible  tube,  instead 
of  to  d. 

bb.  Carbonates  whose  JBases  form  insoluble  Salts  with  Suljjhuric  Acid. 

The  analysis  of  such  carbonates  cannot  well  be  effected  by  the  method 
aa , as  the  insoluble  sulphate  formed  (sulphate  of  lime,  for  instance) 
partially  protects  the  yet  un decomposed  portion  of  the  carbonate  from 
decomposition.  The  apparatus  is  therefore  modified  as  shown  in  fig.  54. 

The  alteration  consists  simply  in  the  tube  a , which  contains  a bulb, 
and  is  drawn  out  to  a fine  point  at  the  lower  end. 

The  process  is  conducted  as  follows  : The  weighed  substance  is  put  into 
A,  together  with  water.  The  bulb-tube  a contains  an  amount  of  dilute 
nitric  acid,  more  than  sufficient  for  the  decomposition  of  the  carbonate, 
and  which  is  prevented  from  flowing  through  the  narrow  aperture  of  this 

tube  by  the  little  wax  stopper  b*  The 
point  of  this  tube  must  not  at  first  dip 
into  the  water  in  A.  The  apparatus 
having  been  tared  on  the  balance,  the 
tube  a is  carefully  and  cautiously  moved 
down,  until  its  point  nearly  touches  the 
bottom  of  A.  The  wax  stopper  b is  then 
momentarily  raised,  or  the  glass  rod  re- 
moved from  the  india-rubber  cap,  so  as 
to  allow  a small  quantity  of  nitric  acid 
to  flow  out  of  the  tube  a ; and  the  same 
operation  is  repeated,  until  the  carbo- 
nate is  completely  decomposed.  The  con- 
tents of  A are  then  heated  to  incipient 
boiling,  the  stopper  at  b removed,  and 
the  carbonic  acid  sucked  out  of  the  appa- 
ratus as  directed  in  aa.  The  diminution 
pig.  54  of  weight  is  ascertained  when  the  appa- 

ratus is  completely  cooled. 

It  will  be  seen  at  a glance  that  a different  construction  may  also  be  given  to 
the  apparatus  ; that,  for  instance,  the  tube  C may  be  connected,  instead  of 
with  13,  with  a chloride  of  calcium  tube,  or  with  a tube  filled  with  pumice 
stone  or  asbestos  moistened  with  sulphuric  acid ; also,  that  the  substance 
to  be  analyzed  may  be  put  into  a small  tube,  which  stands  upright  at 
first,  or  is  suspended  from  a thread,  but  is  subsequently,  after  taring 
the  apparatus,  upset  or  lowered  into  the  dilute  acid  in  the  fiask  ; also, 
that  the  closing  of  a may  be  effected  by  means  of  a compression  clamp, 
&c. 

The  apparatus  proposed  by  Geissler  f is  very  convenient  (see  fig.  55), 
It  consists  of  two  parts,  A 13  and  C.  C is  ground  into  the  neck  of  A {a), 
so  as  to  close  air-tight,  and  yet  admit  of  being  readily  removed,  for 
the  purpose  of  filling  and  emptying  A.  be  is  a glass  tube,  open  at  both 
ends,  and  ground  water-tight  into  C,  at  the  lower  end  (c) ; it  is  kept  in 
the  proper  position  by  means  of  an  easily  movable  cork,  i.  The  illus- 
tration shows  the  construction  of  the  apparatus  in  other  respects.  The 
cork  e must  fit  air-tight,  as  must  the  tube  d in  the  cork.  The  weighed 

* Or  india-rubber  cap,  with  glass  rod.  See  note,  p.  288 
f Journ.  f.  prakt.  Chem.  60,  35. 


CARBONIC  ACID. 


291 


§ 139.1 

substance  is  put  into  A,  water  added  to  the  extent  indicated  in  the 
engraving,  and  the  substance  shaken  towards  the  side  of  the  flask.  C is 
now  filled  nearly  to  the  top  with  dilute  nitric  acid,  with  the  aid  of  a 
pipette,  after  having  previously  turned  the  cork  i upwards,  without  raising 
b ; the  cork  is  then  again  twisted  down  again,  and  C inserted  into  A ; B is 
filled  somewhat  more  than  half  with  concentra- 
ted sulphuric  acid,  and  b closed  at  the  top  with 
a little  wax  stopper,  or  a piece  of  india-rubber 
tube,  with  a small  glass  rod  inserted  in  it.  After 
taring  the  apparatus,  the  decomposition  is  effect- 
ed by  raising  b a little,  and  thus  causing  acid 
to  pass  from  C into  A.  The  carbonic  acid 
escapes  through  h into  the  sulphuric  acid,  where 
it  is  dried ; it  then  leaves  the  apparatus  through 
d.  After  the  decomposition  has  been  effected, 

A is  cautiously  heated  to  incipient  boiling,  the 
stopper  on  b opened,  and  the  carbonic  acid  still 
remaining  in  the  apparatus  sucked  out  through 
d by  means  of  a small  india-rubber  tube.  The 
apparatus  is  finally  weighed  when  cold. 

If  you  prefer  to  decompose  the  carbonate  with 
hydrochloric  acid,  dry  the  escaping  gas  with  the 
pumice-stone  saturated  with  anhydrous  sulphate 
of  copper  (see  aa ),  which  also  retains  hydro- 
chloric acid  as  well  as  the  moisture  (Stolba*). 

It  is  well  to  fill  a light  IJ  -tube  with  this  material. 

The  size  of  the  U-tube  should  depend  on  the 
size  of  the  apparatus.  It  can  be  used  as  long  as  a 
third  of  its  contents  remains  uncolored. 

[cc.  Carbonates  which  dissolve  freely  in  cold- 
dilute  acid,  f 

In  the  processes  hitherto  described,  carbonic 
acid  is  determined  by  the  loss  of  weight  of  an  ap- 
paratus which  contains  no  carbonic  acid  gas  at  the 
beginning  and  which  must  be  completely  emptied  of  this  gas  at  the  con- 
clusion of  the  analysis.  It  is  a matter  of  experience,  however,  that  accu- 
rate results  are  not  attainable  with  certainty  in  this  way.  Nothing 
short  of  actual  boiling  for  some  time  will  expel  all  carbonic  acid  gas  from 
the  dilute  acid  liquid.  This  cannot  be  done  conveniently  without  loss  of 
aqueous  vapor.  The  fact  that  good  results  are  often  obtained  is  due  to 
the  compensation  of  opposite-errors,  as  the  analyst  may  convince  himself 
by  repeatedly  heating  and  sucking  through  air.  If  the  suction  go  on  to 
just  the  right  extent,  the  loss  of  the  apparatus  will  exactly  correspond 
to  the  carbonic  acid  that  was  contained  in  the  substance,  but  further 
exhaustion  of  the  air  will  diminish  the  weight  of  the  apparatus,  not  by 
complete  removal  of  the  carbonic  acid,  but  by  loss  of  aqueous  vapor, 
which  easily  escapes  the  desiccating  material.  By  continued  working 
on  a carbonate  of  known  composition  one  may  soon  learn  how  long  to 
exhaust  in  order  to  bring  out  the  proper  loss,  but  where  the  analyst  is 


* Dingler’s  pol.  Joum.  164,  128. 

f American  Journal  of  Science  and  Arts,  Vol.  xlviil,  July,  1869. 


292 


DETERMINATION. 


[§  139. 


out  of  practice,  an  error  of  1 to  2 per  cent,  is  not  unlikely  to  happen, 
and  the  process  itself  furnishes  no  means  of  judging  when  it  will  give  a 
correct  result. 

The  editor  employs  a simple  modification  of  this  method,  which,  under 
proper  conditions,  gives  very  accurate  results  and  furnishes  to  a great 
extent  its  own  control.  The  process  is  novel  in  this  particular,  viz.: 
the  charged  apparatus  is  in  the  first  place  filled  with  carbonic  acid  gas, 
the  substance  is  then  decomposed,  and  as  soon  as  disengagement  of  gas 
ceases,  the  apparatus,  still  filled  with  carbonic  acid  gas,  is  weighed 
again.  In  this  manner  all  aspiration  is  done  away  with,  and  the  desic- 
cating material  has  simply  to  dry  as  much  gas  as  is  yielded  by  the  sub- 
stance under  analysis. 

It  is,  however,  essential  that  the  substance  under  examination  dissolve 
freely  and  completely  in  cold  acid  ; it  is  likewise  necessary  that  the 
analysis  and  weighings  be  conducted  in  an  apartment  not  liable  to 
change  of  temperature. 

The  apparatus  may  consist  of  a light  flask  or  bottle  with  wide  mouth 
which  is  closed  by  a soft  rubber  stopper,  through  which  there  passes,  on 
the  one  hand,  a chloride  of  calcium  tube,  the 
lower  bulb  of  which  contains  cotton,  and,  on 
the  other,  the  neck  of  a vessel  which  contains 
the  dilute  acid.  This  acid  reservoir  is  so  con- 
structed that  on  suitably  inclining  it,  its  con- 
tents will  flow  freely  into  the  flask.  For  this 
purpose  the  tube  connecting  with  the  latter 
has  an  internal  diameter  of  seven  millimetres, 
and  its  extremity  is  cut  oflf  obliquely  ; at  its 
other  end,  the  acid  reservoir  terminates  in  an 
upturned  narrow  tube,  b.  This  and  the  upper 
termination  of  the  GaCl  tube  are  chosen  of 
such  diameter  that  they  fit  quite  snugly  into 
short,  narrow  and  thick- walled  rubber  connect- 
ors which  are  again  provided  with  glass-rod  stop- 
pers ; all  these  joints  must  be  gas-tight.  In 
figure  56  the  apparatus  is  represented  in  one- 
third  its  proper  dimensions. 

The  weighed  substance,  in  case  of  carbonate 
of  lime,  e.  g .,  is  placed  at  the  bottom  of  the 
flask,  most  conveniently  in  the  form  of  small 
fragments.  The  acid  vessel  is  nearly  filled 
with  hydrochloric  acid  of  sp.  gr.  IT.  It  and 
the  CaCl  tube  are  tightly  adjusted  to  the  neck  of  the  flask,  and  the 
glass-rod  stoppers  being  removed,  the  apparatus  is  connected  at  c with 
a self-regulating  generator  of  washed  carbonic  acid,  and  a rather  rapid 
stream  of  the  gas  is  transmitted  through  the  apparatus  for  15  minutes, 
or  until  the  liquid  in  b is  saturated  and  the  air  is  thoroughly  displaced. 
Then  the  opening  at  d is  stopped  and  afterward  the  apparatus  is  dis- 
connected with  the  carbonic  acid  generator  and  stopped  at  c.  During 
these  as  well  as  the  subsequent  operations,  the  apparatus  must  be  so 
handled  that  its  temperature  shall  not  change.  It  is  immediately 
weighed.  When  removed  from  the  balance,  loosen  the  stopper  at  d , and, 
holding  the  flask  by  a wooden  clamp,  incline  it  so  that  the  acid  may 
flow  over  upon  the  carbonate.  The  decomposition  should  proceed  slow* 


Fig.  56. 


§ 139.] 


CARBONIC  ACID. 


293 


ly,  so  that  the  escaping  gas  may  be  thoroughly  dried.  As  soon  as  solu- 
tion of  the  carbonate  is  complete,  replace  the  stopper  at  d , and  weigh 
again.  Should  there  be  any  leak  in  the  apparatus  the  fact  is  made  evi- 
dent by  a slow  but  steady  loss  of  weight,  when  it  is  brought  upon  the 
balance.  If  all  the  joints  are  sufficiently  tight,  the  weight  remains  the 
same  for  at  least  fifteen  minutes. 

When  properly  executed  the  process  gives  extremely  accurate  results  ; 
a slight  change  of  temperature  or  of  atmospheric  pressure  between  the 
two  weighings  of  course  greatly  impairs  the  results  or  renders  them 
worthless.  Since  the  apparatus  usually  rises  a little  in  temperature 
during  the  solution  of  the  carbonate,  it  is  better,  as  soon  as  the  substance 
is  decomposed,  to  stopper  the  CaCl  tube  and  let  the  whole  stand  fifteen 
minutes,  then  to  connect  as  before  with  the  gas-generator  and  pass  dried 
C02  for  a minute,  and  finally  to  stopper  again  and  bring  upon  the  bal- 
ance. In  seven  analyses  of  pure  calcite  in  quantities  ranging  from  05 
to  0*9  grm.,  the  editor  obtained  the  following  percentages  of  carbonic 
acid,  viz.:  44*07,  44*07,  43*98,  44*01,  44*04,  44*11,  44*16 ; calculation 
requires  44*00. 

In  case  of  alkali-carbonates  which  absorb  carbonic  acid  gas,  it  is 
necessary  to  modify  the  apparatus.  Instead  of  the  light  flask  «,  we  may 
employ  a small  bottle  of  thick  glass  and  wider  mouth,  and  a thrice-per- 
forated rubber  stopper.  Through  the  third  orifice  pass  a narrow  tube  3 to 
4 inches  long  enlarged  below  to  a small  bulb  to  contain  the  carbonate. 
This  bulb  must  be  so  thin  that  on  pushing  down  the  tube  within  the 
bottle  it  shall  be  easily  crushed  to  pieces  against  the  bottom  of  the  lat- 
ter. The  carbonate  is  weighed  into  the  bulb-tube,  the  latter  is  wiped 
clean,  down  to  the  bulb,  corked  and  fixed  in  the  stopper.  The  apparatus 
is  filled  as  before  with  C02  and  weighed.  Then  the  bulb  is  broken  and 
the  process  finished  as  before  described.  In  three  estimations  on  car- 
bonate of  soda  the  editor  found  41*54,  41*64  and  41*58  per  cent,  of  C02. 
Calculation  requires  41*51  per  cent.] 

e.  From  all  Eases  without  exception  {Estimation  of  the  Acid  from  the 
increase  of  weight  of  an  Absorption  Apparatus). 

The  arrangement  of  the  apparatus  I employ  will  be  seen  from  fig.  57.' 

a is  the  evolution  flask  (300  c.  c.)  closed  with  a doubly-perforated 
india-rubber  cork,  bb  is  a tube  twice  bent  and  expanded  at  c to  a small 
bulb,  it  may  be  connected  by  means  of  an  india-rubber  tube  as  required 
either  with  the  little  funnel  d , or  with  the  tube  e,  which  is  filled  with 
soda-lime  or  hydrate  of  potassa.  The  U-tube/'is  filled,  as  regards  the 
bulbed  limb,  with  pieces  of  fused  chloride  of  calcium  ; as  regards  the 
other  limb,  with  fragments  of  pumice  saturated  with  anhydrous  sulphate 
of  copper  (see  p.  289).  The  U-tube  g contains  pieces  of  glass,  6 — 10 
drops  of  concentrated  sulphuric  acid,  and  two  little  asbestos  stoppers, 
the  tube  h is  filled  with  about  20  grm.  coarsely  granulated  soda-lime, 
and  towards  the  outer  end  the  remaining  is  filled  with  coarsely 
granulated  chloride  of  calcium,  k contains  in  the  outward  limb  soda- 
lime,  in  the  inner,  chloride  of  calcium,  ^serves  to  free  the  escaping 
carbonic  acid  from  moisture  and  hydrochloric  acid,  g enables  the  opera- 
tor to  see  the  rate  of  the  evolution  of  gas,  h,  by  its  soda-lime,  takes  up 
the  carbonic  acid  completely,  and  by  its  chloride  of  calcium  prevents 
any  evaporation  of  water  from  the  former  (the  soda-lime  gets  warm  on 
absorbing  the  carbonic  acid),  k serves  to  protect  the  tube  h (which  has 


294 


DETERMINATION. 


[§  139. 


to  be  weighed)  from  any  moisture,  &c.,  which  might  penetrate  from  out- 
side. The  corks  of  g , h and  k must  be  covered  with  sealing-wax.* 
The  absorption  apparatus  is  that  given  by  Mulder,  f and  is  here  espe- 
cially suitable,  as  the  carbonic  acid  is  mixed  with  much  air,  and  the 
evolution  is  at  times  somewhat  rapid. 


Fig.  57. 

After  the  weighed  substance  has  been  transferred  to  a,  and  a little  water 
has  been  added  to  it,  weigh  h and  g together,  and  connect  the  several  parts 
of  the  apparatus — a stands  on  a wire  gauze,  placed  on  a tripod,  e is 
fastened  to  a support,  the  U-tubes  are  suspended  in  a suitable  manner — 
join  b to  d,  and  pour  into  d a small  portion  of  mercury,  just  enough  to 
close  the  tube  at  i.  Now  pour  into  d common  hydrochloric  or  nitric  acid 
(previously  diluted  with  an  equal  bulk  of  water),  and  by  gentle  suction 
through  an  india-rubber  tube  at  l cause  a small  quantity  of  acid  to  flow 
into  the  flask  b.  The  evolution  of  carbonic  acid  commences  immediately ; 
its  rate  may  be  seen  from  g ; if  necessary,  a gentle  heat  may  be  applied. 
When  the  evolution  begins  to  abate,  introduce  more  acid  into  the  flask  in 
the  same  manner  as  before.  As  soon  as  the  carbonate  is  perfectly  decom- 
posed, fill  d several  times  with  hot  water,  causing  it  to  flow  into  a.  This 
is  done  in  order  to  wash  into  a the  small  quantities  of  hydrochloric  acid 
which  remain  in  c,  and  which  possibly  might  have  taken  up  some  carbonic 
acid.  Now  remove  d and  connect  e with  b instead^  heat  the  contents  of  a 
to  gentle  boiling,  which  is  to  be  continued  till  the  first  bulb  of  t/*is  hot, 
and  then  by  sucking  at  l , draw  air  through  the  apparatus  to  the  extent  of 
six  times  the  volume  that  a contains.  This  suction  is  best  effected  by  an 
aspirator.  When  this  has  been  done,  separate* a from/*,  allow  h to  cool 
completely,  remove  h and  g , and  weigh  them  together.  The  increase  of 
weight  of  these  is  the  exact  expression  of  the  carbonic  acid  in  the  sub- 
stance. The  accuracy  of  the  results  leaves  nothing  to  be  desired.  We 
have  the  bases  without  any  impurity,  and  completely  dissolved  in  hydro- 
chloric or  nitric  acid. 

The  tube  g is,  after  use,  closed  at  both  ends,  and  retains  its  utility  a long 


* Or  caoutchouc  stoppers  may  be  used.  For  small  U-tubes,  half  an  inch  of 
fleshy  india-rubber  tubing  forms  an  excellent  joint, 
f Zeitschrift  f.  analyt.  Chem.  1,  2. 


TABLE  OF  THE  ABSORPTION  OF  CARBONIC  ACID 


139.] 


CARBONIC  ACID. 


20f» 


05 

CO 

00 

to 

hH 

o 

l- 

O 

03 

O 

'tH 

o 

tH 

O 

03 

id 

to 

o’ 

00 

o’ 

to’ 

rH 

|r- 

o 

CO 

05 

to 

05 

03 

05 

05 

tr- 

05 

o 

r“l 

CO 

id’ 

o 

o 

*- 

lO 

05 

to* 

GO 

O 

o 

CO 

,-H 

CO 

oo 

03 

CO 

hH 

00 

tr- 

00 

o 

rH 

h* 

CO 

io 

o 

O 

t- 

lO 

05 

to 

co 

00 

Ot 

o 

t- 

CO 

rH 

tr. 

IH 

!>- 

t^ 

q 

rH 

co 

io 

o 

o 

tH 

o’ 

05 

o’ 

I'- 

i- 

co 

rH 

05 

to 

rH 

to 

rH 

to 

to 

tr- 

to 

q 

rH 

CO 

o’ 

o 

o’ 

lO 

05 

id 

03 

to 

rH 

05 

t— 

to 

■o 

o 

Id 

rH 

o 

h)H 

o 

to 

O 

q 

to 

rH 

co 

o 

o 

O* 

1- 

o 

05 

IQ* 

o 

to 

GO 

GO 

O 

o 

hH 

00 

rH 

hH 

tH 

to 

q 

r—i 

rH 

co 

co 

o 

o 

o’ 

l- 

O 

05 

id* 

HO 

1 — 1 

CO 

00 

to 

hH 

co 

t- 

co 

rH 

co 

CO 

CO 

to 

CO 

q 

rH 

CO 

CO 

o 

o 

o’ 

1- 

o’ 

05 

id* 

id 

rH 

r- 

o 

CO 

£ 

03 

id 

03 

rH 

03 

co 

03 

to 

03 

q 

o 

rH 

CO* 

CO 

o* 

o 

o’ 

l- 

o’ 

05 

id 

HO 

o 

o 

to 

03 

O 

rH 

rH 

rH 

rH 

CO 

rH 

to 

rH 

q 

rH 

CO 

co 

o’ 

O 

o’ 

o’ 

O 

id* 

§ 

05 

o 

03 

O 

o 

03 

o 

© 

o 

co 

o 

to 

o 

q 

4 

r_l 

CO* 

CO 

o 

o 

o’ 

o’ 

05 

id’ 

05 

— 1 

1 

05 

05 

© 

05 

© 

05 

CO 

05 

to 

j 05 

00 

10s 

03 

CO* 

03 

o 

'tH 

o’ 

to 

o’ 

I GO 

Id’ 

rH 

CO 

to 

03 

05 

T- 1 

oo 

05 

00 

© 

GO 

CO 

00 

o 

00 

°°. 

03* 

03 

o 

o 

to 

o’ 

00 

Id* 

00 

rH 

00 

o 

• 

Jr. 

© 

t^ 

CO 

tH 

o 

t— 

00 

&* 

03 

03 

o’ 

hH 

o 

to 

o 

oo 

Id’ 

03 

CO 

o 

t^ 

Id 

to 

to 

to 

© 

to 

CO 

to 

o 

to 

°°. 

cq 

03* 

03 

o* 

o’ 

to 

o’ 

oo 

id* 

t^ 

o 

GO 

o 

CO 

V 

id 

hH 

id 

© 

O 

03 

o 

o 

Id 

00 

03 

03 

o’ 

r^H 

O 

to 

o’ 

00 

Id* 

to 

rH 

CO 

tn 

03 

co 

'tH 

05 

03 

hh 

o 

Id 

03* 

03 

H 

-tH 

o’ 

to 

o’ 

00 

id* 

§ 

to 

t>- 

to 

03 

o 

CO 

1— 1 

CO 

05 

co 

03 

CO 

o 

co 

CO 

03* 

03 

o’ 

to 

o’ 

00 

Id* 

o 

to 

o 

rH 

05 

03 

© 

03 

05 

03 

03 

03 

o 

03 

tr- 

03* 

03 

o* 

to 

o 

00 

ld’ 

id 

o 

o 

oo 

00 

rH 

05 

rH 

03 

rH 

o 

rH 

tr- 

rH 

03 

o’ 

CO 

o’ 

00 

ld 

• 

. 

. 

• 

• 

. 

. 

. 

. 

. 

TO 

. 

T3 

. 

T3 

t3 

n 

TO 

03 

T 3 

<D 

T3 

03 

T3 

03 

"d 

© 

<o 

rO 

03 

© 

rf 

03 

rO 

<03 

rQ 

>■ 

Sh 

t> 

H 

> 

H 

H 

o 

O 

O 

P— H 

O 

r-H 

o 

'o 

to 

ro 

ta 

o 

w 

o 

M 

o 

«3 

> 

rO 

> 

r^ 

> 

rO 

> 

rO 

> 

rO 

<1 

<1 

H 

Temperature  Cent. 


296 


DETERMINATION. 


[§  139. 


TABLE  OF  THE  WEIGHT  OF  A CUBIC 
in  Milligrammes  from  720  to  770  mm.  of  pi'essure 
Millimetres. 


720 

722 

724 

726 

728 

730 

732 

734 

736 

738 

740 

742 

744 

10° 

1.77446 

1.77945 

1.78445 

1.78944 

1.79443 

1.79942 

1.80441 

1.80941 

1.81440 

1.81940 

1.82438 

1.82937 

1.83437 

11° 

1.76668 

1.77165 

1.77662 

1.78160 

1.78657 

1.79155 

1.79652 

1.80149 

1.80647 

1.81144 

1.81642 

1.82139 

1.82636 

12° 

1.75881 

1.76377 

1.76873 

1.77368 

1.77864 

1.78359 

1.78855 

1.79351 

1.79846 

1.80342 

1.80838 

1.81333 

1.81829 

13° 

1.75092 

1.75587 

1.76081 

1.76576 

1.77070 

1.77565 

1.78059 

1.78554 

1.79048 

1.79543 

1.80037 

1.80532 

1.81026 

14° 

1.74301 

1.74795 

1.75288 

1.75781 

1.76275 

1.76768 

1.77261 

1.77754 

1.78248 

1.78741 

1.79234 

1.79728 

1.80221 

15° 

1.73502 

1.73993 

1.74484 

1.74974 

1.75465 

1.75955 

1.76446 

1.76937 

1.77427 

1.77918 

1.78408 

1.78899 

1.79390 

16° 

1.72699 

1.73188 

1.73677 

1.74166 

1.74655 

1.75144 

1.75633 

1.76122 

1.76611 

1.77100 

1.77590 

1.78078 

1.78567 

17° 

1.71888 

1.72376 

1.72862 

1.73349 

1.73836 

1.74322 

1.74809 

1.75296 

1.75783 

1.76269 

1.76756 

1.77243 

1.17729 

18° 

1.71069 

1.71554 

1.72040 

1.72525 

1.73011 

1.73497 

1.73982 

1.74468 

1.74953 

1.75439 

1.75925 

1.76410 

1.76896 

19° 

1.70239 

1.70723 

1.71207 

1.71691 

1.72175 

1.72659 

1.73143 

1.73627 

1.74111 

1 

1.74595 

1 

1.75078 

1.75562 

1.76046 

20° 

1.69412 

1.69894 

1.70377 

1.70859 

1.71341 

1.71823 

1.72305 

1.72788 

1.73270 

1.73725 

1.74234 

1.74716 

1.75199 

21° 

1.68571 

1.69051 

1.69532 

1.70012 

1.70493 

1.70974 

1.71454 

1.71935 

1.72415 

1.72896 

1.73377 

1.73857 

1.74338 

22° 

1.67722 

1.68201 

1.68680 

1.69151 

1.69638 

1.70117 

1.70596 

1.71075 

1.71554 

1.72033 

1.72512 

1.72991 

1.73470 

23° 

1.66862 

1.67340 

1.67817 

1.68294 

1.68772 

1.69249 

1.69727 

1.70204 

1.70681 

1.71159 

1.71636 

1.72114 

1.72591 

24° 

1.66994 

1.66470 

1.66945 

1.67421 

1.67897 

1.68372 

1.68848 

1.69324 

1.69799 

1.70275 

1.70751 

1.71227 

1.71702 

25° 

1.65113 

1.65587 

1.66061 

1.66535 

1.67009 

1.67484 

| 

1.67958 

1.68432 

1.68906 

1.69380 

1.69854 

1.70329 

1.70803 

720 

722 

724 

726 

728 

730 

732 

734 

736 

1 

j 73S 

1 

740 

742 

744 

Millimetres. 


§ 139.] 


CARBONIC  ACID. 


297 


CENTIMETRE  OE  CARBONIC  ACID 


of  mercury , and  from  10°  to  25°  Cent. 

Millimetres. 


746 

748 

750 

752 

754 

756 

758 

760 

762 

764 

766 

768 

770 

1.83936 

1.84435 

1.849341.85433 

1.86933 

1.86432 

1.86931 

1.87430 

1.87930 

1.88429 

1.88928 

1.89427 

1.89926 

10° 

1.83134 

1.83631 

1.84129  1.84626 

1.85123 

1.85621 

1.86118 

1.86616 

1.87113 

1.87610 

1.88108 

1.88605 

1.89103 

ii° 

1.82324 

1.82820 

1.83315 

1.83811 

1.84307 

1.84802 

1.85298 

1.85793 

1.86289 

1.86785 

1.87280 

1.87776 

1.88271 

12° 

1.81521 

1.82015 

1.82510 

1.83004 

1.83499 

1.83993 

1.84488 

1.84982 

1.85477 

1.85971 

1.86466 

1.86960 

1.87455 

13® 

1.80714 

1.81208 

1.81701 

1.82194 

1.82687 

1.83181 

1.83674 

1.84167 

1.84661 

1.85154 

1.85647 

1.86141 

1.86634 

14® 

1.79880 

1.80371 

1.80861 

1.81352 

1.81843 

1.82333 

1.82824 

1.83314 

1.83805 

1.84296 

1.84786 

1.85277 

1.85767 

15® 

1.79056 

1.79545 

1.80034 

1.80523 

1.81012 

1.81501 

1.81990 

1.82479 

1.82968 

1.83457 

1.83946 

1.84435 

1.S4924 

16° 

1.78216 

1.78703 

j 1.79189 

1.79676 

1.80163 

1.80650 

1.81136 

1.81623 

1.82110 

1.82596 

1.83083 

1.83570 

1.84056 

17® 

1.77381 

1.77867 

1.78353 

1.78838 

1.79324 

1.79809 

1.80295 

1.80781 

1.81266 

1.81752 

1.82237 

1.82723 

1.83209 

18® 

1.76530 

1.77014 

1.77498 

1.77982 

1.78466 

1.78950 

1.79434 

1.79917 

1.80401 

1.80885 

1.81369 

1.81853 

1.82337 

19® 

1.75681 

1.76113 

1.76645 

1.77127 

1.77610 

1.78092 

1.78574 

1.79056 

1.79538 

1.80021 

1.80503 

1.80985 

1.81467 

20® 

1.74818 

1.75299 

1.75780 

1.76260 

1.76741 

1.77221 

1.77702 

1.78183 

1.78663 

1.79144 

1.79624 

1.80105 

1.80586 

21® 

1.73949 

,1.74428 

1.74907 

1.75386 

1.75865 

1.76344 

1.76823 

1.77302 

1.77781 

1.78260 

1.78739 

1.79218 

1.79697 

22® 

1.73068 

1.73546 

1.74023 

1.74501 

1.74978 

1.75455 

1.75933 

1.76410 

1.76888 

1.77365 

1.77842 

1.78320 

1.78797 

23® 

1.72178 

1.72654 

1.73129 

1.73605 

1.74081 

1.74556 

1.75032 

1.75508 

1.75984 

1.76459 

1.76935 

1.77411 

1.77886 

24° 

1.71277 

1.71751 

1.72225 

1.72699 

1.73173 

1.73648 

1.74122 

1.74596 

1.75070 

1.75544 

1.76018 

1.76492 

1.76967 

25° 

746 

748 

750 

752 

754 

756 

758 

760 

762 

764 

766 

768 

770 

Millimetres. 


Temperature  Cent. 


298 


DETERMINATION. 


time.  The  tube  h can  also  be  used  repeatedly  without  being  refilled. 
The  second  time  it  is  employed  connect  it,  for  the  sake  of  precaution,  with 
a separately  weighed  tube  of  the  small  kind.  The  latter  rarely  increases  in 
weight,  and  the  first  tube  can,  therefore,  be  then  used  a third  time.  If 
after  this  the  second  tube  has  become  heavier,  at  the  fourth  operation 
reject  the  first  tube,  and  use  the  second  tube  alone,  and  so  on. 

When  large  quantities  of  carbonic  acid  are  to  be  absorbed,  the  tube  g 
may  be  replaced  with  advantage  by  a Liebig’s  potash  apparatus. 

f.  Separation  from  all  Bases  without  exception  ( Estimation  of  the  Acid 
by  Expulsion , Absorption , and  Volumetric  Analysis'). 

It  is  sometimes  advantageous,  especially  in  the  estimation  of  very 
small  quantities  of  carbonic  acid,  to  receive  the  same  in  a known  volume 
of  standard  lime-  or  baryta-water,  and  to  complete  the  analysis  according 
to  Pettenkofer’s  principle  (I.,  6,  j3). 

g.  Estimation  by  Measuring  the  Gas. 

This  process  is  applicable  in  the  case  of  all  salts  which  are  decomposed 
by  hydrochloric  acid  in  the  cold.  It  is  distinguished  for  rapid  and  con- 
venient execution  and  very  satisfactory  results.  [The  azotometer,  fig.  58, 


is  employed,  and  the  details  of  the  process  are  for  the  most  part  similar 
to  those  followed  in  the  estimation  of  ammonia  as  described  on  page  159. 
The  weighed  carbonate  is  put  in  the  bottle  a,  and  the  tube  f is  charged 


SILICIC  ACID. 


299 


§ 140.1 


with.  5 c.c.  of  H.  Cl.,  sp.  gr.  M25.  When  the  burette  is  adjusted  to  zero, 
the  acid  is  poured  at  once  upon  the  carbonate.  The  precautions  to  be 
observed  in  the  measurement  of  the  gas  are  as  detailed  on  page  161. 
It  is  not  needful  to  wait  so  long  for  the  gas  to  cool.  The  necessary 
corrections  are  applied  by  aid  of  the  foregoing  tables  given  by  Dietrich,* 
pp.  295-6-7.  Their  use  is  perfectly  similar  to  that  of  the  tables  given 
on  pages  160  and  162-3.] 


§ 140. 

2.  Silicic  Acid. 

I.  Determination. 

The  direct  estimation  of  silicic  acid  is  invariably  effected  by  con- 
verting the  soluble  modification  of  the  acid  into  the  insoluble  modifica- 
tion, by  evaporating  and  completely  drying ; the  insoluble  modification  is 
then,  after  removal  of  all  foreign  matter,  ignited  and  weighed. 

For  the  guidance  of  the  student  I would  observe  here  that,  to  guard 
against  mistakes,  he  should  always  test  the  purity  of  the  weighed  silicic  acid. 
The  methods  of  testing  will  be  found  below. 

If  you  have  free  silicic  acid  in  the  state  of  hydrate,  in  an  aqueous  or 
acid  solution  free  from  other  fixed  bodies,  simply  evaporate  the  solution  in 
a platinum  dish,  ignite  and  weigh  the  residue. 

II.  Separation  of  Silicic  Acid  from  the  Bases. 

a.  In  all  compounds  which  are  decomposed  by  Hydrochloric  or  Nitric 
Acid , on  digestion  in  open  vessels. 

To  this  class  belong  the  silicates  soluble  in  water,  as  well  as  many  of  the 
insoluble  silicates,  as,  for  instance,  nearly  all  zeolites. 

The  compound  under  examination  is  very  finely  pulverized,  the  powder 
dried  at  100°  (not  above),  and  put  into  a platinum  or  porcelain  dish  (in 
the  case  of  silicates  whose  solution  might  be  attended  with  disengagement 
of  chlorine,  platinum  cannot  be  used) ; a little  water  is  then  added,  and 
the  powder  mixed  to  a uniform  paste.  Moderately  concentrated  hydro- 
chloric acid,  or — if  the  substance  contains  lead  or  silver — nitric  acid,  is 
now  added,  and  the  mixture  digested  at  a very  gentle  heat,  with  constant 
stirring,  until  the  substance  is  completely  decomposed,  in  other  terms  until 
the  glass  rod,  which  is  rounded  at  the  end,  encounters  no  more  gritty 
powder,  and  the  stirring  proceeds  smoothly  without  the  least  grating. 

The  silicates  of  this  class  do  not  all'  comport  themselves  in  the  same 
manner  in  this  process,  but  show  some  differences  ; thus  most  of  them 
form  a bulky  gelatinous  mass,  whilst  in  the  case  of  others  the  silicic 
acid  separates  as  a light  pulverulent  precipitate;  again, many  of  them 
are  decomposed  readily  and  rapidly,  whilst  others  require  protracted 
digestion. 

When  the  decomposition  is  effected,  the  mixture  is  evaporated  to  dry- 
ness on  the  water-bath,  and  the  residue  heated,  with  frequent  stirring, 
until  all  the  small  lumps  have  crumbled  to  pieces,  and  the  whole  mass  is 
thoroughly  dry,  and  until  no  more  acid  fumes  escape.  It  is  always  the 
safest  way  to  conduct  the  operation  of  drying  on  the  water-bath.  Occa- 
sionally it  is  well  to  moisten  the  dry  mass  with  water  and  evaporate  again. 


* Fres.  Zeitschrift,  iv.,  11,  142-145. 


300 


DETERMINATION. 


In  cases  where  it  appears  desirable  to  accelerate  the  desiccation  by  the  ap- 
plication of  a stronger  heat,  as  when  deliquescent  chlorides  are  present, 
an  air-bath  may  be  had  recourse  to ; which  may  be  constructed  in  a 
simple  way,  by  suspending  the  dish  containing  the  substance,  with  the 
aid  of  wire,  in  a somewhat  larger  dish  of  silver  or  iron,  in  a manner  to 
leave  everywhere  between  the  two  dishes  a small  space  of  uniform  width. 
Direct  heating  over  the  lamp  is  not  advisable,  as  in  the  most  strongly 
heated  parts  the  silicic  acid  is  liable  to  unite  again  with  the  separated 
bases  to  compounds  which  are  not  decomposed,  or  only  imperfectly,  by 
hydrochloric  acid. 

When  the  mass  is  cold,  it  is  brought  to  a state  of  semi-fluidity  by 
thoroughly  moistening  it  with  hydrochloric  acid ; after  which  it  is  allowed 
to  stand  for  half  an  hour,  then  warmed  on  a water-bath,  diluted  with  hot 
water,  stirred,  allowed  to  deposit,  and  the  fluid  decanted  on  to  a filter  ; the 
residuary  silicic  acid  is  again  stirred  with  hot  water,  and  the  fluid  once 
more  decanted  ; after  a third  repetition  of  the  same  operation,  the  preci- 
pitate also  is  transferred  to  the  filter,  thoroughly  washed  with  hot  water, 
well  dried,  and  ignited  at  last  as  strongly  as  possible,  as  directed  in  § 52  or 
in  § 53.  For  the  properties  of  the  residue,  see  § 93,  9.  The  results  are 
accurate.  The  bases,  which  are  in  the  filtrate  as  chlorides,  are  determined 
by  the  methods  given  above.  Deviations  from  the  instructions  here  given 
are  likely  to  entail  loss  of  substance  ; thus,  for  instance,  if  the  mass  is  not 
thoroughly  dried,  a not  inconsiderable  portion  of  the  silicic  acid  passes  into 
the  solution,  whereas  if  the  instructions  are  strictly  complied  with,  only 
traces  of  the  acid  are  dissolved ; in  accurate  analyses,  however,  even  such 
minute  traces  must  not  be  neglected,  but  should  be  separated  from  the 
bases  precipitated  from  the  solution.  This  separation  may  be  readily 
effected  by  dissolving  them,  after  ignition  and  weighing,  in  hydrochloric 
or  sulphuric  acid,  by  long  digestion  in  the  heat ; the  minute  portion  of 
silicic  acid  is  left  undissolved.  Again,  if  the  silicic  acid  is  not  thoroughly 
dried  previous  to  ignition,  the  aqueous  vapor  disengaged  upon  the  rapid 
application  of  a strong  heat  may  carry  away  particles  of  the  light  and  loose 
silica. 

The  purity  of  the  silicic  acid  * may  be  conveniently  tested  in  the  fol- 
lowing manner  : — Heat  a moderately  concentrated  solution  of  pure  carbo- 
nate of  soda  to  boiling,  in  a silver  or  platinum  dish,  or  in  a porcelain  dish, 
and  add  a small  quantity  of  the  silicic  acid.  If  it  dissolves  completely, 
this  is  a proof  of  its  purity  ; but  if  it  leaves  a residue,  the  remainder  of 
the  silicic  acid  must  be  weighed,  and  the  amount  of  impurity  determined 
as  directed  in  6,  and  the  result,  of  course,  calculated  to  the  whole  amount 
of  the  silica. 

If  you  have  pure  hydrofluoric  acid,  you  may  also  test  the  purity  of  the 
silicic  acid  in  a very  easy  manner,  by  treating  it  with  this  acid  and  some 
sulphuric  acid  in  a platinum  dish  ; upon  the  evaporation  of  the  solution, 
the  silicic  acid,  if  pure,  will ‘volatilize  completely  (as  fluoride  of  silicon). 
If  a residue  remains,  moisten  this  once  more  with  hydrofluoric  acid,  add  a 
few  drops  of  sulphuric  acid,  evaporate,  and  ignite ; the  residue  consists  of 
the  sulphates  of  the  bases  which  were  mixed  with  the  silicic  acid,  as  well 
as  any  titanic  acid  that  was  present  (Berzelius). 


* This  testing  is  more  especially  necessary  in  cases  where  the  silicic  acid  has 
separated,  not  in  the  gelatinous  state,  but  in  the  pulverulent  form. 


SILICIC  ACID. 


301 


§ 140.] 


b.  Compounds  which  are  not  decomposed  by  Hydrochloric  Acid  or 
Nitric  Acid , on  digestion  in  open  vessels. 

a.  Decomposition  by  Fusion  with  Alkaline  Carbonate. 

Reduce  the  substance  to  an  impalpable  powder,  by  trituration  and 
sifting  (§  25)  ; transfer  to  a platinum  crucible,  and  mix  with  about  4 times 
the  weight  of  pure  anhydrous  carbonate  of  soda,  with  the  aid  of  a rounded 
glass  rod  ; wipe  the  rod  against  a small  portion  of  the  carbonate  of  soda 
on  a card,  and  transfer  this  also  from  the  card  to  the  crucible.  Cover  the 
latter  well,  and  heat,  according  to  size,  over  a gas-  or  spirit-lamp  with 
double  draught,  or  a blast  gas-lamp  ; or  insert  in  a Hessian  crucible, 
compactly  filled  up  with  calcined  magnesia,  and  heat  in  a charcoal  fire. 

Apply  at  first  a moderate  heat  for  some  time  to  make  the  mass  simply 
agglutinate  ; the  carbonic  acid  will,  in  that  case,  escape  from  the  porous 
mass  with  ease  and  unattended  with  spirting.  Increase  the  heat  after- 
wards, finally  to  a very  high  degree,  and  terminate  the  operation  only 
when  the  mass  appears  in  a state  of  calm  fusion,  and  gives  no  more 
bubbles. 

The  platinum  crucible  in  which  the  fusion  is  conducted  must  not  be  too 
small ; in  fact,  the  mixture  should  only  half  fill  it.  The  larger  the  crucible, 
the  less  risk  of  loss  of  substance.  As  it  is  of  importance  to  watch  the 
progress  of  the  operation,  the  lid  must  be  easily  removable;  a concave 
cover,  simply  lying  on  the  top,  is  therefore  preferable  to  an  overlapping 
lid.  In  heating  over  a lamp,  the  crucible  should  always  be  supported  on 
a triangle  of  platinum  wire  (see  fig.  40,  p.  64),  with  the  opening  just 
sufficiently  wide  to  allow  the  crucible  to  drop  into  it  fully  one-third,  yet 
to  retain  it  firmly,  even  with  the  wire  at  an  intense  red  heat.  When  con- 
ducting the  process  over  a simple  gas-lamp,  it  is  advisable,  towards  the 
end  of  the  operation,  when  the  heat  is  to  be  raised  to  the  highest  degree, 
to  put  a chimney  over  the  crucible,  with  the  lower  border  resting  on 
the  ends  of  the  iron  triangle  which  supports  the  platinum  triangle  ; this 
chimney  should  be  about  12  or  14  cm.  high,  and  the  upper  opening  meas- 
ure about  4 cm.  in  diameter. 

When  the  fusion  is  ended,  the  red-hot  crucible  is  removed  with  tongs, 
and  placed  on  a cold,  thick,  clean  iron  plate,  on  which  it  will  rapidly 
cool ; it  is  then  genially  easy  to  detach  the  fused  cake  in  one  piece. 

The  cake  (or  the  crucible  with  its  contents)  is  put  into  a beaker,  from 
10  to  15  times  the  quantity  of  water  poured  over  it,  and  hydrochloric  acid 
gradually  added,  or,  under  certain  circumstances,  nitric  acid  ; the  beaker 
is  kept  covered  with  a large  watch-glass  or  porcelain  dish,  perfectly  clean 
outside,  to  prevent  the  loss  of  the  drops  of  fluid  which  the  escaping  car- 
bonic acid  carries  along  with  it ; the  drops  thus  intercepted  by  the  cover 
are  afterwards  rinsed  into  the  beaker.  The  crucible  is  also  rinsed  with 
dilute  acid,  and  the  solution  obtained  added  to  the  fluid  in  the  beaker. 

The  solution  is  promoted  by  the  application  of  a gentle  heat,  which  is 
continued  for  some  time,  to  insure  the  expulsion  of  the  carbonic  acid  ; 
since  otherwise  some  loss  of  substance  might  be  incurred,  in  the  subse- 
quent evaporation,  by  spirting. 

If  in  treating  the  fused  mass  with  hydrochloric  acid,  a powder  subsides 
(chloride  of  sodium  or  chloride  of  potassium),  more  water  is  required. 

If  the  decomposition  of  the  mineral  has  succeeded,  the  hydrochloric 
solution  is  either  perfectly  clear,  or  light  flakes  of  silicic  acid  only  float 
in  it.  But  if  a heavy  powder  subsides,  which  feels  gritty  under  the 


302 


DETERMINATION. 


[§  140. 

glass  rod,  this  consists  of  undecomposed  mineral.  The  cause  of  such 
imperfect  decomposition  is  generally  to  be  ascribed  to  imperfect  pulveri- 
zation. 

In  such  cases  the  undecomposed  portion  may  be  fused  once  more  with 
carbonated  alkali  ; the  better  way,  however,  is  to  repeat  the  process  with 
a fresh  portion  of  mineral  more  finely  pulverized. 

The  hydrochloric  or  nitric  solution  is  poured,  together  with  the  pre- 
cipitate of  silicic  acid,  into  a porcelain,  or,  better,  into  a platinum  dish, 
and  treated  as  directed  in  II.,  a . 

That  the  fluid  may  not  be  too  much  diluted,  the  beaker  should  be  rinsed 
only  once,  or  not  at  all,  and  the  few  remaining  drops  of  solution  dried  in 
it ; the  trifling  residue  thus  obtained  is  treated  in  the  same  way  as  the 
residue  left  in  the  evaporating  basin. 

This  is  the  method  most  commonly  employed  to  effect  the  decomposition 
of  silicates  that  are  undecomposable  by  acids ; that  it  cannot  be  used  to 
determine  alkalies  in  silicates  is  evident. 

(3.  Decomposition  by  means  of  Hydrofluoric  Acid. 

The  finely-pulverized  silicate  is  mixed,  in  a platinum  dish,  with  rather 
concentrated,  slightly  fuming  hydrofluoric  acid,  the  acid  being  added 
gradually,  and  the  mixture  stirred  with  a thick  platinum  wire.  The  mix- 
ture, which  has  the  consistence  of  a thin  paste,  is  digested  some  time  on  a 
water-bath  at  a gentle  heat,  and  pure  concentrated  sulphuric  acid,  diluted 
with  an  equal  quantity  of  water,  is  then  added,  drop  by  drop,  in  more  than 
sufficient  quantity  to  convert  all  the  bases  present  into  sulphates.  The 
mixture  is  evaporated  on  the  water-bath  to  dryness,  during  which 
operation  fluoride  of  silicon  gas  and  hydrofluoric  acid  gas  are  continually 
volatilizing  ; it  is  finally  exposed  to  a stronger  heat  at  some  height  above 
the  lamp,  until  the  excess  of  sulphuric  acid  is  almost  completely  ex- 
pelled. The  mass,  when  cold,  is  thoroughly  moistened  with  concentrated 
hydrochloric  acid,  and  allowed  to  stand  for  one  hour ; water  is  then  added, 
and  a gentle  heat  applied.  If  the  decomposition  has  fully  succeeded, 
the  whole  must  dissolve  to  a clear  fluid.  If  an  undissolved  residue  is 
left,  the  mixture  is  heated  for  some  time  on  the  water-bath,  then  allowed 
to  deposit,  the  clear  supernatant  fluid  decanted  as  far  as  practicable, 
the  residue  dried,  and  then  treated  again  with  hydrofluoric  acid  and  sul- 
phuric acid,  and,  lastly,  with  hydrochloric  acid,  which  will  now  effect 
complete  solution,  provided  the  analyzed  substance  was  very  finely  pul- 
verized, and  free  from  baryta,  strontia,  (and  lead).  The  solution  is  added 
to  the  first.  The  bases  in  the  solution  (which  contains  them  as  sulphates, 
and  contains  also  free  hydrochloric  acid)  are  determined  by  the  methods 
which  will  be  found  in  Section  V. 

The  hydrofluoric  acid  may  also  be  employed  in  combination  with  hydro- 
chloric acid ; thus  1 grm.  of  finely  elutriated  felspar,  mixed  with  40  c.  c. 
water,  7 c.  c.  hydrochloric  acid  of  25£  and  3^-  c.  c.  hydrofluoric  acid,  and 
heated  to  near  the  boiling  point,  dissolves  completely  in  three  minutes. 
4 c.  c.  sulphuric  acid  are  then  added,  the  sulphate  of  baryta  which  sepa- 
rates is  filtered  off,  and  the  filtrate  evaporated  till  no  more  hydrofluoric 
acid  escapes  (Al.  Mitscherlich  *). 

The  execution  of  the  method  requires  the  greatest  possible  care,  both 
the  liquid  and  the  gaseous  hydrofluoric  acid  being  most  injurious  sub- 


* Joum.  f.  prakt.  Chem.  81,  108. 


SILICIC  ACID. 


303 


§ ho.] 

stances.  The  treatment  of  the  silicate  with  the  acid  and  the  evaporation 
must  be  conducted  in  the  open  air,  otherwise  the  windows  and  all  glass 
apparatus  will  be  attacked.  As  the  silicic  acid  is  in  this  method  simply 
inferred  from  the  loss,  a combination  with  the  method  a is  often  resorted 
to.  [See  also  § 160,  85.] 

[y.  Decomposition  by  ignition  with  Carbonate  of  Dime  and  Chloride 
of  Ammonium.  Prof.  J.  L.  Smith’s  Method  for  separating  alkalies. 

Mix  1 part  of  the  pulverized  silicate  with  1 part  of  dry  chloride  of 
ammonium,*  by  gentle  trituration  in  a smooth  mortar,  then  add  8 parts 
of  carbonate  of  lime  (Qual.  Anal.  p.  83)  and  mix  intimately.  Bring  the 
mixture  into  a platinum  crucible,  rinsing  the  mortar  with  a little  car- 
bonate of  lime.  Warm  the  crucible  gradually  over  a small  Bunsen  burn- 
er until  fumes  of  ammonia-salts  no  longer  appear,  then  heat  to  full  red- 
ness, but  not  too  intensely,  for  from  30  to  40  minutes,  f The  mass  should 
sinter  together,  but  not  fuse.  When  cold  it  may  be  usually  detached  with 
ease  from  the  crucible.  It  is  heated  to  boiling  in  a capsule  with  100  c.  c. 
of  water  for  several  hours,  or  until  it  is  entirely  disintegrated  and  no 
lumps  remain.  Should  the  mass,  from  overheating,  remain  partially  co- 
herent after  long  boiling,  it  may  be  transferred  to  a porcelain  mortar  and 
ground  finely,  and  then  boiled  as  before.  Certain  silicates,  e.  g.  those  con- 
taining much  protoxide  of  iron,  fuse  easily  with  the  proportions  of  flux 
above  given.  In  their  case  it  is  better  to  repeat  the  ignition  on  a new 
portion,  using  10  or  12  parts  of  carbonate  of  lime  and  bringing  only  the 
lower  three-fourths  of  the  crucible  to  a red  heat. 

The  fluxed  mass,  when  completely  disintegrated  by  boiling  with  water, 
yields  to  this  solvent  all  the  alkalies,  with  some  chloride  of  calcium  and 
caustic  lime.  It  is  filtered  and  well  washed.  To  the  liquid  is  added  carbonate 
of  ammonia  (1 — 2 grms.)  in  solution,  and  the  whole  is  evaporated  to  a 
bulk  of  about  30  c.  c.  Then  a little  more  carbonate  of  ammonia,  with 
some  caustic  ammonia,  is  added,  to  insure  complete  separation  of  the  lime. 
Filter  and  collect  the  filtrate  and  washings  in  a weighed  platinum  cap- 
sule, evaporate  to  dryness  on  the  water-bath,  dry  further,  supporting  the 
capsule  within  an  iron  cup  to  which  heat  is  applied,  and  finally  heat  care- 
fully almost  to  redness,  to  expel  ammonia-salts.  When  cool,  weigh.  The 
alkali-chlorides  thus  obtained  are  nearly  pure ; but  on  dissolving  in  a few 
drops  of  water,  a little  black  residue  is  usually  seen.  This  may  be  re- 
moved, if  weighable,  by  filtration,  using  a very  small  filter.  Prof. 
Smith’s  method  is  by  far  the  most  convenient  and  accurate  for  separa- 
ting alkalies  from  a silicate,  and  is  universally  applicable,  except,  perhaps, 
in  presence  of  boracic  acid.] 


* The  chloride  of  ammonium  is  best  obtained  in  a pulverulent  condition  by  dis- 
solving- some  of  the  salt  in  hot  water  and  evaporating-  rapidly  ; the  greater  portion 
of  the  chloride  of  ammonium  will  deposit  itself  in  a pulverulent  condition,  the 
water  is  poured  off,  and  the  salt  thrown  on  bibulous  paper,  allowed  to  dry ; the 
final  desiccation  being  carried  on  in  a water-bath,  or  in  any  other  way  with  a 
corresponding  temperature. 

f An  ordinary  portable  furnace,  with  a conical  sheet-iron  cap,  of  from  two  to 
three  feet  high,  likewise  answers  the  purpose  perfectly  well,  all  the  requisite 
heat  being  afforded  by  it. 


304 


DETERMINATION. 


[§  141 


Second  Group. 

Hydrochloric  Acid — Hydrobromic  Acid — Hydriodic  Acid — Hydro- 
cyanic Acid — Hydrosulphuric  Acid. 

§ 141.- 

1.  Hydrochloric  Acid. 

I.  Determination. 

Hydrochloric  acid  may  be  determined  very  accurately  in  the  gravimetric 
as  well  as  in  the  volumetric  way.* 

a.  Gravimetric  Method. 

Determination  as  Chloride  of  Silver. 

Solution  of  nitrate  of  silver,  mixed  with  some  nitric  acid,  is  added  in 
exoess  to  the  solution  under  examination,  the  precipitated  chloride  is  made 
to  unite  by  application  of  heat  and  shaking,  washed  by  decantation,  dried, 
and  ignited.  The  details  of  the  process  have  been  given  in  § 115, 1,  a,  a. 
Care  must  be  taken  not  to  heat  the  solution  mixed  with  nitric  acid,  before 
the  solution  of  nitrate  of  silver  has  been  added  in  excess.  As  soon  as  the 
latter  is  present  in  excess,  the  chloride  of  silver  separates  immediately  and 
completely  upon  shaking  the  vessel,  and  the  supernatant  fluid  becomes  per- 
fectly clear  after  standing  a short  time  in  a warm  place.  The  determina- 
tion of  hydrochloric  acid  by  means  of  silver  is  therefore  more  readily 
effected  than  that  of  silver  by  means  of  hydrochloric  acid.  In  the  case  of 
smaller  quantities  of  chloride  of  silver,  the  precipitate  is  often  collected  on 
a filter ; see  § 115,  1,  a,  |3.  Or  the  two  methods  maybe  combined  in  this 
way — that  the  chief  portion  of  the  precipitate  is  washed  by  decantation, 
dried  in  the  porcelain  crucible,  and  ignited,  the  decanted  fluid  being 
passed  through  a filter,  to  make  quite  sure  that  not  a particle  of  chloride 
of  silver  be  lost.  The  filter  is,  after  drying,  incinerated  on  the  inverted 
cover  of  the  porcelain  crucible,  the  ashes  are  treated  with  a few  drops  of 
nitric  acid,  some  hydrochloric  acid  is  added,  the  mixture  evaporated  to 
dryness,  the  residue  gently  ignited,  and  the  lid  replaced  on  the  crucible  in 
which  the  chloride  has  been  heated  to  incipient  fusion  ; a gentle  heat 
is  then  once  more  applied,  after  which  the  crucible  is  allowed  to  cool  under 
the  desiccator,  and  then  weighed. 

b.  Volumetric  Methods. 

a.  Dy  Solution  of  Nitrate  of  Silver. 

This  convenient  and  accurate  method  requires  a perfectly  neutral  solu- 
tion of  nitrate  of  silver  of  known  value.  [This  is  best  prepared  by 
weighing  off  in  a porcelain  crucible  about  4*8  grm.  of  Glean  crystallized 
nitrate  of  silver,  fusing  it  at  the  lowest  possible  heat,  and  then  ascertain- 
ing its  weight  accurately.  After  fusion  it  should  weigh  a little  more  than 
4*7933  grm.,  the  quantity  that,  contained  in  a litre  of  water,  gives  a so- 
lution of  which  1 c.  c.  =*001  grm.  of  chlorine.  The  fused  salt  is  dis- 
solved in  a little  warm  water,  the  solution  brought  into  a litre  flask  and 
filled  to  the  mark,  observing  the  usual  precautions  as  to  temperature, 
&c.  When  thus  adjusted,  add  to  the  contents  of  the  flask,  from  a bu- 
rette, enough  water  to  bring  the  excess  of  nitrate  of  silver  above  4*7933 
grms.  to  the  requisite  dilution. 


* For  the  acidimetric  estimation  of  free  hydrochloric  acid,  see  § 204. 


§ 1«.] 


HYDROCHLORIC  ACID. 


305 


gran.  c.  c.  gran.  c.  c. 

4*7933  : 1000  ::  Excess  over  4*7933  : Excess  over  1000. 

Tn  this  way  it  is  easy  with  a burette  and  a litre  flask  to  make  a per- 
fectly accurate  standard  solution,  while  this  would  be  hardly  possible 
should  the  operator  weigh  off  less  than  4*7933  grm.  of  nitrate  of  silver. 

This  solution,  which  may  be  preserved  in  a well-corked  bottle  indefi- 
nitely, without  change,  is  next  tested  by  means  of  pure  chloride  of  sodi- 
um. Either  an  equivalent  solution  is  made  by  dissolving  T6486  grm. 
of  the  coarsely  powdered  and  gently  ignited  salt  in  1 litre  of  water,  and 
portions  of  20  c.  c.  are  taken,  or  several  portions  of  the  dry  salt,  0*05 
grm.,  are  weighed  off  and  dissolved,  each  in  a separate  beaker,  in  20 — 30  c. 
c.  of  water.  To  each  solution  2 drops  of  a cold  saturated  solution  of  pure 
yellow  chromate  of  potassa  is  added.] 

Fill  a Mohr’s  burette  (if  it  has  an  Erdmann’s  float  so  much  the  better) 
up  to  zero  with  the  silver  solution,  and  allow  to  drop  slowly,  with  con- 
stant stirring,  into  the  light  yellow  solution  contained  in  one  of  the 
beakers.  Each  drop  produces,  where  it  falls,  a red  spot,  which  on  stir- 
ring disappears,  owing  to  the  instant  decomposition  of  the  chromate  of 
silver  with  the  chloride  of  sodium.  At  last,  however,  the  slight  red  col- 
oration remains.  Now  all  chlorine  has  combined  with  silver,  and  a little 
chromate  of  silver  has  been  permanently  formed.  [The  number  of  c.  c.  of 
silver  solution  should  be  equal  to  the  number  of  milligrammes  of  chlorine 
in  the  Na  Cl  employed.  An  excess  of  about  0*2  c.  c.  of  silver  solution  will 
be  required  to  produce  a visible  coloration,  and  hence  this  quantity  may 
be  deducted  from  the  amount  used.  Should  repeated  trials  show  that 
the  silver  solution  is  not  of  exactly  the  intended  strength,  it  may  be 
brought  to  the  precise  standard  by  addition  of  water  or  nitrate  in  requi- 
site quantity.  It  is,  however,  ordinarily  better  to  take  the  mean  of 
several  accordant  determinations  of  the  quantity  of  chlorine  precipitated 
by  1 c.  c.  of  the  silver  solution,  and  write  this  number  on  the  label  of  the 
bottle,  to  be  employed  as  a factor  into  which  the  no.  of  c.  c.  of  silver  so- 
lution required  in  any  analysis  is  to  be  multiplied  to  find  the  quantity  of 
chlorine  sought  for.] 

Being  now  in  possession  of  a standard  silver  solution,  and  being  practised 
in  exactly  hitting  the  transition  from  yellow  to  the  shade  of  red,  we  can 
determine  with  precision  hydrochloric  acid  or  chlorine  in  the  form  of  a 
metallic  chloride  soluble  in  water.  The  fluid  to  be  tested  must  be  neu- 
tral— free  acids  dissolve  the  chromate  of  silver.  The  solution  of  the  sub- 
stance is  therefore,  if  necessary,  rendered  neutral  by  addition  of  nitric 
acid  or  carbonate  of  soda  (it  should  be  rather  alkaline  than  acid),  about 
2 drops  of  the  solution  of  yellow  chromate  added,  and  then  silver  from 
the  burette,  till  the  reddish  coloration  is  just  perceptible. 

If  the  operator  fears  he  has  added  too  much  silver  solution,  i.e.,  if  the 
red  color  is  too  strongly  marked,  he  may  add  1 c.  e.  of  a solution  of 
chloride  of  sodium  containing  1*6486  in  a litre  (and  therefore  corre- 
sponding to  the  silver  solution),  and  then  add  the  silver  drop  by  drop 
again.  Of  course  in  this  case  1 c.  c.  must  be  deducted  from  the  amount 
of  silver  solution  used. 

The  results  are  very  satisfactory. 

The  fluid  to  be  analysed  should  be  about  the  same  volume  as  the  solu- 
tions employed  in  standardizing  the  silver  solution,  and  also  about  the 
same  strength,  otherwise  the  small  quantity  of  silver  which  produces  the 

20 


306 


DETERMINATION. 


[§  141. 


coloration  will  not  stand  in  the  same  proportion  to  the  chlorine  present. 
This  small  quantity  of  silver  solution  is  extremely  small,  about  0’20  c.  c., 
the  inaccuracy  hereby  arising  even  in  the  case  of  quantities  of  chlorine 
differing  widely  from  that  originally  used  in  standardizing  the  silver  so- 
lution is  therefore  almost  inconsiderable.  If  the  amount  of  silver  solu- 
tion necessary  to  impart  the  coloration  always  remained  the  same,  we 
should  have  simply  to  deduct  the  amount  in  question  with  all  experi- 
ments in  order  to  avoid  this  small  inaccuracy  entirely ; since,  however, 
this  is  not  the  case,  but,  on  the  contrary,  much  chloride  of  silver  requires 
somewhat  more  chromate  of  silver  for  visible  coloration,  than  less  chlo- 
ride of  silver,  this  method  of  proceeding  would  not  always  increase  the 
exactness  of  the  results. 

j3.  By  Solution  of  Nitrate  of  Silver  and  Iodide  of  Starch  (Pisani’s 
method*). 

Add  to  the  solution  of  the  chloride,  acidified  with  nitric  acid,  a slight 
excess  of  solution  of  nitrate  of  silver  of  known  strength,  warm,  and  filter. 
Determine  the  excess  of  silver  in  the  filtrate  by  means  of  solution  of  iodide 
of  starch  (seep.  215),  and  deduct  this  from  the  amount  of  silver  solution 
used.  The  difference  shows  the  quantity  of  silver  which  has  combined 
with  the  chlorine  ; calculate  from  this  the  amount  of  the  latter.  Results 
satisfactory . 

Of  these  volumetric  methods  of  estimating  chlorine,  the  first  deserves 
the  preference  in  all  ordinary  cases.  Pisani’s  method  (b,  J3)  is  especially 
suited  for  the  estimation  of  very  minute  quantities  of  chlorine,  but  is  not 
applicable  when — as  in  nitre  analyses — large  quantities  of  alkaline  nitrate 
are  present  (p.  211). 

II.  Separation  of  Chlorine  from  the  Metals . 
a.  In  Soluble  Chlorides . 

The  same  method  as  in  I.,  a.  The  metals  in  the  filtrate  are  separated 
from  the  excess  of  the  salt  of  silver  by  the  methods  which  will  be  found 
in  Section  V. 

Bichloride  of  tin , chloride  of  mercury , the  chlorides  of  antimony,  and 
the  green  chloi'ide  of  chromium , form  exceptions  from  the  rule. 

a.  From  solution  of  bichloride  of  tin,  nitrate  of  silver  would  precipitate, 
besides  chloride  of  silver,  a compound  of  binoxide  of  tin  and  oxide  of 
silver.  To  precipitate  the  tin,  therefore,  the  solution  is  mixed  with  a 
concentrated  solution  of  nitrate  of  ammonia,  allowed  to  deposit,  the  fluid 
decanted,  and  filtered  (compare  § 126,  1,  b),  and  the  chlorine  in  the  fil- 
trate is  precipitated  with  solution  of  silver.  Lowenthal,  the  inventor  of 
this  method,  has  proved  its  accuracy. \ 

8.  When  a solution  of  chloride  of  mercury  is  precipitated  with  solution 
of  nitrate  of  silver,  the  chloride  of  silver  thrown  down  contains  an  admix- 
ture of  mercury.  The  mercury  is,  therefore,  first  precipitated  by  sul- 
phuretted hydrogen,  which  must  be  added  in  sufficient  excess,  and  the 
chlorine  in  the  filtrate  determined  as  directed  in  § 169. 


* Annal.  d.  Mines,  X.  83  ; Liebig  and  Kopp’s  Jahresbericht  f.  1856,  751. 
f .Journ.  f.  prakt.  Chem  , 56,  -37L 


142.1 


FREE  CHLORINE. 


307 


y.  The  chlorides  of  antimony  are  also  decomposed  in  the  manner  de- 
scribed in  3.  The  separation  .of  basic  salt  upon  the  addition  of  water 
may  be  avoided  by  addition  of  tartaric  acid.  The  sulphide  of  antimony 
should  be  tested  for  chlorine. 

S.  Solution  of  silver  fails  to  precipitate  the  whole  of  the  chlorine  from 
solution  of  the  green  chloride  of  chromium  (Peligot).  The  chromium  is, 
therefore,  first  precipitated  with  ammonia,  the  fluid  filtered,  and  the  chlorine 
in  the  filtrate  precipitated  as  directed  in  I.,  a. 

b.  In  Insoluble  Chlorides. 

a.  Chlorides  soluble  in  Nitric  Acid. 

Dissolve  the  chloride  in  nitric  acid,  without  applying  heat,  and  proceed 
as  directed  in  I.,  a . 

3.  Chlorides  insoluble  in  Nitric  Acid  (chloride  of  lead,  chloride  of  silver, 
subchloride  of  mercury). 

aa.  Chloride  of  lead  is  decomposed  by  digestion  with  alkaline  bicar- 
bonate and  water.  The  process  is  exactly  the  same  as  for  the 
decomposition  of  sulphate  of  lead  (§  132.  II.,  &.,  3). 

bb.  Chloride  of  silver  is  ignited  in  a porcelain  crucible,  with  3 parts 
of  carbonate  of  soda  and  potassa,  until  the  mass  commences  to 
agglutinate.  Upon  treating  the  mass  with  water,  the  metallic 
silver  is  left  undissolved ; the  solution  contains  the  alkaline  chloride, 
which  is  then  treated  as  directed  in  I.,  a. 

Chloride  of  silver  may  also  be  readily  decomposed  by  digestion 
with  pure  zinc,  and  dilute  sulphuric  acid.  The  separated  metallic 
silver  may  be  weighed  as  such ; it  must  afterwards  be  ascertained, 
however,  whether  it  dissolves  in  nitric  acid  to  a clear  fluid.  The 
chlorine  is  determined  in  the  solution  of  chloride  of  zinc  obtained, 
as  in  I.,  a. 

cc.  Subchloride  of  mercury  is  decomposed  by  digestion  with  solution 
of  soda  or  potassa.  The  hydrochloric  acid  in  the  filtrate  is  deter- 
mined as  in  I.,  a.  The  suboxide  of  mercury  is  dissolved  in  nitric 
or  nitrohydrochloric  acid,  and  the  mercury  determined  as  directed 
in  § 117  or  § 118. 

c.  The  soluble  chlorides  of  the  metals  of  the  fourth , fifth , and  sixth 
groups  may  generally  be  decomposed  also  by  sulphuretted  hydrogen,  or, 
as  the  case  may  be,  sulphide  of  ammonium.  The  hydrochloric  acid  in 
the  filtrate  is  determined  as  directed  in  § 169.  It  must  not  be  omitted  to 
test  the  precipitated  sulphides  for  chlorine. 

d.  In  many  metallic  chlorides,  for  instance,  in  those  of  the  first  and 
second  groups,  the  chlorine  may  be  determined  also  by  evaporating  with 
sulphuric  acid,  converting  the  base  thus  into  a sulphate,  which  is  then 
ignited  and  weighed  as  such  ; the  chlorine  being  calculated  from  the  loss. 
This  method  is  not  applicable  in  the  case  of  chloride  of  silver  and  chloride 
of  lead,  which  are  only  imperfectly  and  with  difficulty  decomposed  by 
sulphuric  acid  ; nor  in  the  case  of  chloride  of  mercury  and  bichloride  of 
tin,  which  sulphuric  acid  fails  almost  or  altogether  to  decompose. 

Supplement. 

Determination  of  Chlorine  in  the  Free  State, 

§M2. 

Chlorine  in  the  free  state  may  be  determined  both  in  the  volumetric 


DETERMINATION. 


308 


[§  H2. 


and  in  the  gravimetric  way.  The  volumetric  methods,  however,  deserve 
the  preference  in  most  cases.  They  are  very  numerous. 

I shall  only  here  adduce  that  one  which  is  undoubtedly  the  most  accurate 
and  at  the  same  time  the  most  convenient.* 

1.  Volumetric  Method. 

With  Iodide  of  Potassium  ( after  Bunsen). 

Bring  the  chlorine,  in  the  gaseous  form  or  in  aqueous  solution,  into  con- 
tact with  an  excess  of  solution  of  iodide  of  potassium  in  water.  Each  eq. 
chlorine  liberates  1 eq.  iodine.  By  determining  the  liberated  iodine  by 
means  of  hyposulphite  of  soda  as  described  in  § 146,  you  will  learn  the 
quantity  of  chlorine  with  the  greatest  accuracy.  If  you  have  to  deter- 
mine the  chlorine  of  chlorine  water,  measure  a portion  off  with  a pipette. 
To  prevent  any  of  the  gas  entering  the  mouth,  connect  the  upper  end  of 
the  pipette  with  a tube  containing  moist  hydrate  of  potassa  laid  between 
cotton.  When  the  pipette  has  been  correctly  filled  allow  its  contents  to 
flow,  with  stirring,  into  an  excess  of  solution  of  iodide  of  potassium  ( 1 in 
10).  When  the  latter  is  in  excess,  a black  precipitate  is  formed.  If  the 
chlorine  is  evolved  in  the  gaseous  condition,  you  may  employ  either  the 
apparatus  given  in  § 130,  I.,  d , j 3,  or  the  following,  which  is  especially 
suitable  where  the  chlorine  is  not  pure,  but  is  mixed  with  other  gases. 


Fig.  59. 


a is  a little  flask,  from  which  the  chlorine  is  evolved  by  boiling  the 
substance  with  hydrochloric  acid ; it  is  connected  with  the  tube  b by 
means  of  a flexible  tube.  The  latter  must  be  free  from  sulphur — should 
it  contain  sulphur  it  is  well  boiled  with  dilute  potassa  and  then  thoroughly 
washed.  The  thinner  tube  c,  which  has  been  fused  to  the  bulb  of  5, 
leads  through  the  caoutchouc  stopper  (which  has  been  deprived  of  sul- 


* Compare  article  “ Chlorimetry  ” in  the  Special  Part 


HYDROBROMIC  ACID. 


309 


143.] 


phur)  to  the  bulbed  U-tube  d,  which  contains  solution  of  iodide  of  potas- 
sium, and  which  for  safety  is  connected  with  the  plain  U-tube  e,  also 
containing  iodide  of  potassium  solution.  Both  tubes  stand  in  a beaker 
filled  with  water.  The  apparatus  offers  the  advantages  that  the  fluid 
cannot  return,  that  the  iodide  of  potassium  remains  cold,  and  that  the 
absorption  is  complete.  After  all  the  chlorine  has  been  expelled  by 
boiling  long  enough,  rinse  d and  e out  into  a beaker  and  measure  the 
iodine  with  standard  hyposulphite  of  soda  (§  146). 

2.  Gravimetric  Method. 

The  fluid  under  examination,  which  must  be  free  from  sulphuric  acid, 
say,  for  instance,  30  grm.  chlorine  water,  is  mixed  in  a stoppered  bottle, 
with  a slight  excess  of  hyposulphite  of  soda,  say  0*5  grm.,  the  stopper 
inserted,  and  the  bottle  kept  for  a short  time  in  a warm  place ; after 
which  the  odor  of  chlorine  has  disappeared.  The  mixture  is  then  heated 
to  boiling  with  some  hydrochloric  acid  in  excess,  to  destroy  the  excess 
of  hyposulphite  of  soda,  filtered,  and  the  sulphuric  acid  in  the  filtrate 
determined  by  baryta  (§  132).  1 eq.  sulphuric  acid  corresponds  to  2 eq. 
chlorine  (Wicke*). 

In  fluid, s containing , besides  free  chlorine , also  hydrochloric  acid , or  a 
metallic  chloride , the  chlorine  existing  in  a state  of  combination  may  be 
determined,  in  presence  of  the  free  chlorine,  in  the  following  way : — 

A weighed  portion  of  the  fluid  is  mixed  with  solution  of  sulphurous 
acid  in  excess,  the  mixture  acidified,  after  some  time,  with  nitric  acid, 
and  the  whole  of  the  chlorine  precipitated  as  chloride  of  silver.  The 
quantity  of  the  free  chlorine  is  then  determined  in  another  weighed 
portion,  by  means  of  iodide  of  potassium ; the  difference  gives  the 
amount  of  combined  chlorine. f 


Having  thus  seen  in  how  simple  and  accurate  a manner  the  quantity 
of  free  chlorine  may  be  determined  by  Bunsen’s  method,  it  will  be 
readily  understood  that  all  oxides  and  peroxides  which  yield  chlorine 
when  heated  with  hydrochloric  acid,  may  be  analyzed  by  heating  them 
with  concentrated  hydrochloric  acid,  and  determining  the  amount  of 
chlorine  evolved.  For  the  modus  operandi  compare  1. 

§ 143. 

2.  Hydrobromic  Acid. 

I.  Determination. 

a.  As  bromide  of  silver.  Free  hydrobromic  acid — in  a solution  free 
from  hydrochloric  acid  or  chlorides — is  precipitated  by  silver  solution, 
and  the  further  process  is  conducted  as  in  the  case  of  hydrochloric  acid 
(§  141).  For  the  properties  of  bromide  of  silver,  see  § 94,  2.  The 
results  are  perfectly  accurate. 

* Annal.  d.  Chem.  u.  Pharm.  99,  99. 

f If  chlorine  water  is  mixed  at  once  with  solution  of  nitrate  of  silver,  § only 
of  the  chlorine  are  obtained  as  chloride  of  silver : 6 Cl  + 6 Ag  0 = 5 Ag  Cl  -f- 
A g O,  Cl  Of)  (H.  Rose,  Weltzien,  Annal.  d.  Chem.  u.  Pharm.  91,  45).  If  chlorine 
water  is  mixed  with  ammonia  in  excess,  there  are  formed  at  first  chloride  of  am- 
monium and  hypochlorite  of  ammonia,  the  latter  then  gradually  decomposes 
into  nitrogen  and  chloride  of  ammonium ; however,  a little  chlorate  of  ammo- 
nia is  also  formed  besides  (Schonbein,  Journ.  f.  prakt.  Chem.  84,  386);  Zeit- 
schrift  f.  analyt.  Chem.  2 , 59. 


310 


DETERMINATION. 


[§  143 

The  following  methods  are  especially  serviceable  for  the  determination 
of  small  amounts  of  bromine;  they  are  applicable  in  the  presence  of 
chlorides. 

b.  With  chlorine  water  and  chloroform  {after  A.  Reimann* * * §).  This 
method  depends  on  the  facts  that  chlorine  when  added  to  bromides  first 
liberates  the  bromine  and  then  combines  with  it,  and  that  bromine  colors 
chloroform  yellow  or  orange,  while  chloride  of  bromine  merely  commu- 
nicates a yellowish  tinge  to  that  fluid.  The  process  is  as  follows : — Mix 
the  liquid  containing  a bromide  of  an  alkali  metal  in  neutral  solution,  in 
a stoppered  bottle  with  a drop  of  pure  chloroform  about  the  size  of  a 
hazel-nut,  then  add  standard  chlorine  water  from  a burette,  protected 
from  the  light  by  being  surrounded  with  black  paper.  On  shaking, 
the  chloroform  becomes  yellow,  on  further  addition  of  chlorine  water, 
orange,  then  yellow  again,  and  lastly — at  the  moment  when  2 eq.  chlo- 
rine have  been  used  for  1 eq.  bromine — yellowish  white  (K  Br  -f-  2 Cl  — 
K Cl  -f-  Br  Cl).  Considerable  practice  and  skill  are  required  before  the 
operator  can  tell  the  end-reaction.  He  will  be  assisted  by  placing  the 
bottle  on  white  paper  and  comparing  the  color  of  the  chloroform  with 
that  of  a dilute  solution  of  yellow  chromate  of  potassa  of  the  required 
color.  The  strength  of  the  chlorine  water  should  depend  on  the  amount 
of  the  bromine  to  be  determined.  It  should  be  so  adjusted  that  about 
100  c.  c.  may  be  used.  The  chlorine  water  is  standardized  with  iodide 
of  potassium  and  hyposulphite  of  soda  (§  142,  1).  The  method  is  es- 
pecially suited  for  the  determination  of  small  quantities  of  bromine  in 
mother  liquors,  kelp,  &c.  The  results  are  very  approximate  : e.g .,  0*0180 
instead  of  0*0185 — 0*055  instead  of  0*059 — 0*0112  instead  of  0*0100,  &c. 
If  the  fluid  contains  organic  substances,  it  is — after  being  rendered  alka- 
line with  caustic  soda — evaporated  to  dryness,  the  residue  ignited  in  a 
silver  dish,  extracted  with  water,  the  solution  neutralized  exactly  with 
hydrochloric  acid,  and  then  tested. 

c.  Heine’s  colorimetric  method. f The  bromine  is  liberated  by  means 
of  chlorine,  and  received  in  ether;  the  solution  is  compared,  with  re- 
spect to  color,  with  an  ethereal  solution  of  bromine  of  known  strength, 
and  the  quantity  of  bromine  in  it  thus  ascertained.  FehlingJ  obtained 
satisfactory  results  by  this  method.  It  will  at  once  be  seen  that  the 
amount  of  bromine  contained  in  the  fluid  to  be  analyzed  must  be  known 
in  some  measure,  before  this  method  can  be  resorted  to.  As  the  brine 
examined  by  Fehling  could  contain  at  the  most  0*02  grm.  bromine  in 
60  grm.,  he  prepared  ten  different  test  fluids,  by  adding  to  ten  several 
portions  of  60  grm.  each  of  a saturated  solution  of  common  salt  increas- 
ing quantities  of  bromide  of  potassium,  containing  respectively  from 
0*002  grm.  to  0*020  grm.  bromine.  He  added  an  equal  volume  of  ether 
to  the  test  fluids,  and  then  chlorine  water,  until  there  was  no  further 
change  observed  in  the  color  of  the  ether.  It  being  of  the  highest  im- 
portance to  hit  this  point  exactly,  since  too  little  as  well  as  too  much 
chlorine  makes  the  color  appear  lighter,  Fehling  prepared  three  samples 
of  each  test  fluid,  and  then  chose  the  darkest  of  them  for  the  compari- 
son. 60  grm.  are  now  taken§  of  the  mother  liquor  to  be  examined,  the 

* Anna!  d.  Chem.  u.  Pharm.  115,  140. 

f Journ.  f.  prakt.  Chem.  36,  184,  proposed  to  effect  the  determination  of  bro- 
mine in  mother  liquors. 

f:  Journ.  f.  prakt.  Chem.  45,  269. 

§ The  best  way  is  to  take  them  by  measure. 


HYDRIODIC  ACID. 


311 


§§  144,  145.] 


same  volume  of  ether  added  as  was  added  to  the  test  fluids,  and  then 
chlorine  water.  Every  experiment  is  repeated  several  times.  Direct 
sunlight  must  be  avoided,  and  the  operation  conducted  with  proper  ex- 
pedition. In  my  opinion  it  is  well  to  replace  the  ether  by  chloroform 
or  bisulphide  of  carbon. 

II.  Separation  of  Bromine  from,  the  Metals. 

The  metallic  bromides  are  analzyed  exactly  like  the  corresponding 
chlorides  (§  141,  II.,  a to  d ),  the  whole  of  these  methods  being  appli- 
cable to  bromides  as  well  as  chlorides.  In  the  decomposition  of  bro- 
mides by  sulphuric  acid  (§  141,  II.,  d ),  porcelain  crucibles  must  be  used 
instead  of  platinum  ones,  as  the  latter  would  be  attacked  by  the  liber- 
ated bromine. 


Supplement. 

Determination  of  Free  Bromine. 

§ 144. 

Free  bromine  in  aqueous  solution,  or  evolved  in  the  gaseous  form,  is 
caused  to  act  on  excess  of  solution  of  iodide  of  potassium.  Each  eq. 
bromine  liberates  1 eq.  iodine,  which  is  most  conveniently  determined 
by  means  of  hyposulphite  of  soda  (§  146).  As  regards  the  best  mode 
of  bringing  about  the  action  of  the  bromine  on  the  iodide  of  potassium, 
compare  § 142,  1. 

The  determination  of  free  bromine  in  presence  of  hydrobromic  acid 
or  metallic  bromides  is  effected  in  the  same  manner  as  that  of  free 
chlorine  in  presence  of  hydrochloric  acid  (see  § 142,  at  the  end). 

§ 145. 

3.  Hydriodic  Acid. 

I.  Determination. 

a.  As  Iodide  of  Silver,  Gravimetrically. — If  you  have  hydriodic 
acid  in  solution,  free  from  hydrochloric  and  hydrobromic  acids,  precipi- 
tate with  nitrate  of  silver,  and  proceed  exactly  as  with  hydrochloric 
acid  (§  141).  For  the  properties  of  iodide  of  silver,  see  § 94,  3.  The 
results  are  perfectly  accurate. 

b.  As  Protiodide  of  Palladium,  Gravimetrically. — The  following 
method,  recommended  first  by  Lassaigne,  is  resorted  to  exclusively  to 
effect  the  separation  of  hydriodic  acid  from  hydrochloric  and  hydrobromic 
acids,  for  which  purpose  it  is  extremely  well  adapted.  Acidify  the  solu- 
tion slightly  with  hydrochloric  acid,  and  add  a solution  of  protochloride  of 
palladium,  as  long  as  a precipitate  forms  ; let  the  mixture  stand  from  24 
to  48  hours  in  a warm  place,  filter  the  brownish-black  precipitate  off  on  a 
weighed  filter,  wash  with  warm  water,  and  dry  at  a temperature  from 
about  70°  to  80°,  until  the  weight  remains  constant.  The  drying  may  be 
greatly  facilitated  by  replacing  the  water  (after  the  operation  of  washing) 
by  some  alcohol,  and  the  latter  fluid  again  by  a little  ether.  For  the  pro- 
perties of  the  precipitate,  see  § 94,  3.  This  method  gives  very  accurate 
results,  provided  the  drying  be  managed  with  proper  care ; but  if  the 


DETERMINATION. 


312 


[§  145. 


temperature  is  raised  to  near  100°,  the  precipitate  smells  of  iodine,  and  a 
trifling  loss  is  incurred. 

Instead  of  simply  drying  the  protiodide  of  palladium,  and  weigh- 
ing it  in  that  form,  you  may  ignite  it  in  a crucible  of  porcelain  or  pla- 
tinum,* and  calculate  the  iodine  from  the  residuary  metallic  palladium 
(H.  Rose). 

c.  With  Chlorine  Water  and  Chloroform  (after  A.  and  F. 
Dupre-}-).  This  is  based  upon  the  circumstance  that,  when  chlorine 
water  or  solution  of  chloride  of  soda  is  added  to  a metallic  iodide,  the 
first  equivalent  of  chlorine  liberates  iodine,  which  then  combines  with  5 
more  equivalents  of  chlorine  to  pentachloride  of  iodine.  Golfier-Bes- 
seyre  adds  starch  paste  to  render  this  transition  perceptible,  whilst  A.  and 
F.  Dupre  employ,  with  much  better  success,  chloroform  or  bisulphide  of 
carbon,  which  are  colored  intensely  violet  by  free  iodine  as  well  as  by  all 
compounds  of  iodine  with  chlorine  containing  less  than  5 eq.  chlorine. 

The  process  may  be  conducted  in  two  different  ways. 

a.  Add  chlorine  water  to  a few  litres  of  water,  and  determine  the  chlo- 
rine in  the  fluid  as  directed  in  § 142. 

Take  now  of  the  fluid  under  examination  a quantity  containing  no  more 
than  about  10  mgrm.  iodine,  and  pour  this  into  a stoppered  bottle,  add  a 
few  grammes  of  pure  chloroform  or  pure  bisulphide  of  carbon  (free  from 
sulphur  and  sulphuretted  hydrogen),  and  then  gradually,  drop  by  drop, 
chlorine  solution,  adding  and  shaking  vigorously  by  turns,  until  the  violet 
color  of  the  chloroform  or  bisulphide  of  carbon  just  disappears ; which 
point  maybe  hit  with  the  greatest  precision.  6 eq.  chlorine  consumed  in 
this  process  correspond  to  1 eq.  iodine.  A still  simpler  way  is  to  deter- 
mine the  strength  of  the  dilute  chlorine  water  by  making  it  act  upon  a 
known  quantity  of  iodide  of  potassium,  say  10  c.  c.  of  a solution  con- 
taining 0*001  grm.  iodine  in  1 c.  c.,  and  then  to  apply  it  to  the  fluid  under 
examination.  The  amount  of  chlorine  consumed  in  the  first  experiment 
is,  in  that  case,  to  the  known  amount  of  iodine  as  the  quantity  consumed 
in  the  second  experiment  is  to  x. 

In  cases  where  the  quantity  of  iodine  is  so  considerable  as,  when  sepa- 
rated, to  impart  a distinctly  perceptible  coloration  to  the  fluid,  it  is  better 
to  delay  adding  the  chloroform  or  bisulphide  of  carbon,  until  the  color 
first  produced  has  nearly  disappeared  again  upon  further  addition  of 
chlorine  water. 

That  this  method  cannot  be  employed  in  presence  of  substances  liable  to 
be  acted  upon  by  free  chlorine  or  iodine,  is  self-evident ; organic  matters, 
more  particularly,  must  not  be  present.  If  they  are,  as  is  usually  the  case 
with  mother  liquors,  the  method  # should  be  employed. 

P.  Add  to  the  fluid  under  examination  chloroform  or  bisulphide  of 
carbon,  then  dilute  chlorine  water  of  unknown  strength,  until  the  fluid  is 
just  decolorized.  At  this  point  all  the  iodine  is  converted  in  I Cl5.  Add 
now  solution  of  iodide  of  potassium  in  moderate  excess  ; this  will  produce 
for  every  equivalent  of  I Cl5,  6 eq.  free  iodine,  which  remain  dissolved  in 
the  fluid.  Determine  the  liberated  iodine  with  hyposulphite  of  soda 
or  sulphurous  acid,  as  directed  in  § 146,  and  divide  the  quantity  found 
by  6 : the  quotient  expresses  the  quantity  of  iodine  contained  in  the  ex- 
amined fluid. 


* This  substance  is  not  injured  by  the  operation, 
f Anual.  d.  Chem.  u.  Pharm.  94,  365. 


FREE  IODINE. 


313 


§ 146.] 

In  presence  of  bromides,  Dupre’s  method  requires  certain  modifications, 
for  which.  I refer  to  § 169. 

This  method  is  suited  more  particularly  for  the  estimation  of  minute 
quantities  of  iodine.  The  results  are  most  accurate. 

d.  By  Distillation  with  Sesquichloride  of  Iron  (after  Duflos). 
When  hydriodic  acid  or  a metallic  iodide  is  heated,  in  a distillatory 
apparatus,  with  solution  of  pure  sesquichloride  of  iron,  the  whole  of  the 
iodine  escapes  along  with  the  aqueous  vapor  and  protochloride  of  iron 
is  formed  (Fe2  Cl3  + HI  = 2FeCl-fHCl  + I).  The  iodine  passing  over  is 
received  in  solution  of  iodide  of  potassium  (apparatus,  fig.  59,  p.  308), 
and  its  quantity  determined  by  means  of  hyposulphite  of  soda  or  sulphurous 
acid,  as  directed  § 146.  In  employing  this  method,  it  must  be  borne  in 
mind  that  the  sesquichloride  of  iron  must  be  free  from  chlorine  and  nitric 
acid.  It  is  best  to  prepare  it  from  sesquioxide  of  iron  and  hydrochloric 
acid. 

e.  By  Separation  with  Hyponitric  Acid.  See  separation  of  iodine 
from  chlorine,  § 169. 

II.  Separation  of  Iodine  from  the  Metals. 

The  metallic  iodides  are  analyzed  like  the  corresponding  chlorides. 
From  iodides  of  the  alkali  metals  containing  free  alkali  the  iodine  may 
be  precipitated  as  iodide  of  silver,  by  first  saturating  the  free  alkali 
almost  completely  with  nitric  acid,  then  adding  solution  of  nitrate  of 
silver  in  excess,  and  finally  nitric  acid  to  strongly  acid  reaction.  If  an 
excess  of  acid  were  added  at  the  beginning,  free  iodine  might  separate, 
which  is  not  converted  completely  into  iodide  of  sil  ver  by  solution  of 
nitrate  of  silver. 

With  respect  to  the  salts  insoluble  in  water,  I have  to  observe  that 
many  of  them  are  more  advantageously  decomposed  by  boiling  with  potassa 
or  soda,  than  dissolved  in  dilute  nitric  acid,  the  latter  process  being  apt 
to  be  attended  with  separation  of  iodine.  This  applies  more  particularly 
to  subiodide  of  copper  and  to  protiodide  of  palladium.  From  iodides 
soluble  in  water,  the  iodine  may  also  be  precipitated  as  protiodide  of 
palladium. 

Lastly,  it  is  open  to  the  analyst  in  almost  all  cases  to  determine  the 
base  in  one  portion  of  the  compound,  by  heating  with  concentrated  sul- 
phuric acid,  the  iodine,  in  another  portion,  by  the  method  I.,  e.  The 
iodide  of  mercury  is  best  decomposed  by  distillation  with  8 to  10  parts  of 
a mixture  of  1 part  cyanide  of  potassium  with  2 parts  anhydrous  lime. 
Apparatus,  fig.  50,  p.  222  ; a b is  filled  with  magnesite  (H.  Bose  *). 

Supplement. 

Determination  of  Free  Iodine. 

§ 146. 

The  determination  of  free  iodine  is  an  operation  of  great  importance  in 
analytical  chemistry,  since,  as  Bunsen  first  pointed  out,  it  is  a means  for 
the  estimation  of  all  those  substances  which,  when  brought  into  contact  with 
iodide  of  potassium,  separate  from  the  same  a definite  quantity  of  iodine 
(e.g.,  chlorine,  bromine,  &c.),  or,  when  boiled  with  hydrochloric  acid,  yield 


* Zeitschrift  f.  anal.  Chem.  2,  1. 


314 


DETERMINATION. 


[§  146. 


a definite  quantity  of  chlorine  (e.y.,  chromic  acid,  some  peroxides,  &c.). 
By  causing  the  chlorine  produced  to  act  on  iodide  of  potassium,  we  obtain 
the  equivalent  quantity  of  free  iodine. 

Bunsen  and  Schwarz’s  Method. 

This  method  is  based  on  the  following  reaction  2 (NaO  S3  Cb)-f-I  = 
Na  I-f  NaO  S4  05. 

a.  Requisites. 

a.  Iodine  solution  of  known  strengh.  Dissolve  6*2  to  6 *3  grm.  iodine 
with  the  aid  of  about  9 grm.  iodide  of  potassium  (free  from  iodic  acid) 
and  water  to  about  1200  c.  c. 

j3.  Solution  of  hyposulphite  of  soda.  Dissolve  12*2  to  12'3  grm.  of 
the  pure  and  dry  salt  in  water  to  about  1200  c.  c. 

y.  Solution  of  iodide  of  potassium.  Dissolve  1 part  of  the  salt  (free 
from  iodic  acid)  in  about  10  parts  of  water.  The  solution  must  be  col- 
orless and  must  remain  so  immediately  after  the  addition  of  dilute  sul- 
phuric or  hydrochloric  acid  (either  must  be  iron-free). 

6.  Starch  solution.  Stir  the  purest  starch  powder  gradually  with 
about  100  parts  cold  water  and  heat  to  boiling  with  constant  stirring. 
Allow  to  cool  quietly,  and  pour  off  the  fluid  from  any  deposit.  The 
solution  should  be  almost  clear  and  free  from  all  lumps.  The  starch 
solution  is  best  prepared  fresh  before  each  series  of  experiments. 

b.  Preliminary  Determinations. 

a.  Determination  of  the  relation  between  the  Iodine  Solution  and  the 
Hyposulphite  Solution. 

Fill  two  burettes  with  the  solutions.  Bun  20  c.  c.  of  the  hyposul- 
phite into  a beaker,  add  some  water  and  3 or  4 c.  c.  starch  solution, 
then  add  the  iodine  till  a blue  coloration  is  just  produced.  If  you  have 
added  a drop  too  much,  run  in  one  or  two  drops  more  of  the  hyposul- 
phite, and  then  more  cautiously  one  drop  after  another  of  the  iodine 
solution.  After  a few  minutes  read  off  the  height  of  the  fluid  in  both 
burettes.  Suppose  we  had  used  20  c.  c.  hyposulphite  to  20-2  c.  c. 
iodine. 

0.  Exact  Determination  of  the  Iodine  in  the  Solution. 

This  is  performed  by  comparison  with  a known  quantity  of  pure 
iodine ; the  process  is,  as  far  as  my  experience  goes,  best  conducted  in 
the  following  manner  : — 

Select  three  watch-glasses,  a,  5,  and  c,  which  fit  each  other ; weigh  b 
and  c together  accurately.  Put  about  0*5  grm.  pure  dry  iodine  (pre- 
pared according  to  § 65,  6)  into  a,  place  it  on  an  iron  plate  and  heat  gen- 
tly, till  dense  fumes  of  iodine  escape.  Now  cover  it  with  b and  regulate 
the  heat  so  that  the  iodine  may  sublime  entirely  or  almost  entirely  into 
b.  Next  remove  b , while  still  hot,  give  it  a gentle  swing  in  the  air,  to 
remove  the  still  uncondensed  iodine  fumes  and  any  traces  of  aqueous 
vapor,  cover  it  with  c , allow  to  cool  under  the  desiccator,  weigh  and 
transfer  the  two  watch-glasses,  together  with  the  weighed  iodine,  to  a 
capacious  beaker,  containing  a sufficient  quantity  of  iodide  of  potassium 
solution  to  dissolve  the  whole  of  the  iodine  to  a clear  fluid.  Now  run 
in  hyposulphite  from  the  burette  till  the  fluid  is  just  decolorized,  add  3 
to  4 c.  c.  starch  solution,  and  then  iodine  solution  from  a second  buret te; 
to  incipient  blueness. 


FREE  IODINE. 


315 


§ 146.] 

After  the  two  burettes  have  been  read  off,  the  following  simple  calcu- 
lation gives  the  strength  of  the  iodine  solution  : — 

Suppose  we  had  weighed  off  0150  grm.  iodine,  and  used  205  c.  c. 
hyposulphite  and  0*3  c.  c.  iodine  solution. 

From  a,  we  know  that  20  c.  c.  hyposulphite  correspond  to  20*2  c.  c. 
iodine  solution;  29*5  c.  c.  therefore  correspond  to  29*8  c.  c. 

Now  29*5  c.  c.  hyposulphite  correspond  to  0*150  grm.  iodine-]- 0*3  c.  c. 
iodine  solution. 

But  29*5  c.  c.  hyposulphite  also  correspond  to  29*8  c.  c.  iodine  solu- 
tion. 

.*.0*150  grm.  iodine+0‘3  c.  c.  iodine  solution=29*8  c.  c.  iodine  solu- 
tion. 

.*.0*150  grm.  iodines 29*5  c.  c.  iodine  solution. 

.*.1  c.  c.  iodine  solution=0*0050847  grm.  iodine. 

The  experiment  just  described  is  repeated  and  the  mean  of  the  two 
results  taken,  provided  they  exhibit  sufficient  uniformity. 

y.  Dilution  of  the  standard  fiuids  to  a convenient  strength. 

With  the  aid  of  the  iodine  solution  the  strength  of  which  we  now 
know  exactly,  and  the  solution  of  hyposulphite  of  soda  which  stands  in 
a known  relation  to  the  same,  we  might  make  any  determinations  of 
iodine.  The  calculation,  although  in  principle  extremely  simple,  is  yet 
somewhat  hampered  by  reason  of  the  long  decimal  which  expresses  the 
quantity  of  iodine  in  1 c.  c.  of  the  solution.  It  is  therefore  convenient 
to  dilute  the  iodine  solution  so  that  1 c.  c.  may  exactly  contain  0*005 
grm.  iodine.  This  is  done  by  filling  a litre  flask  therewith,  and  adding 
the  necessary  quantity  of  water;  in  our  case  16*94  c.  c.,  for  5 : 5*0847 
::  1000  : 1016*94.  If  the  litre  flask  will  hold  above  the  mark,  this 
16*94  c.  c.,  it  is  simply  added,  otherwise  it  is  put  into  the  dry  bottle 
destined  to  receive  the  iodine  solution,  the  iodine  solution  added,  the 
whole  shaken  together,  a portion  of  the  fluid  returned  to  the  flask, 
shaken,  poured  back  into  the  bottle,  and  the  whole  shaken  again. 

The  solution  of  hyposulphite  may  now  be  diluted  in  a corresponding 
manner.  In  our  case  we  should  have  had  to  add  27*11  c.  c.  water  to 
1000  c.  c.  of  the  solution,  as  will  be  seen  from  the  following  considera- 
tion : — 

20*2  c.  c.  of  the  original  iodine  solution  correspond  to  20  c.  c.  of  the 
hyposulphite  solution. 

.*.1000  c.  c.  correspond  to  990*1  c.  c. 

Now  these  1000  c.  c.  were  made  up  to  1016*94  by  addition  of  water ; 
if  therefore  we  make  up  990*1  c.  c.  of  the  hyposulphite  of  soda  to  the 
same  bulk  by  addition  of  water  we  shall  have  equivalent  solutions. 
Hence,  to  990*1  c.  c.  we  must  add  26*84  c.  c.  water,  or  to  1000  c.  c. 
27*11  water. 

In  such  cases  of  dilution,  I always  prefer  to  take  exactly  1 litre  in- 
stead of  an  uneven  number  of  c.  c.,  as  in  measuring  the  latter  errors  and 
inaccuracies  may  readily  occur;  I have  therefore,  above,  recommended 
the  preparation  of  1200  c.  c.  of  the  fluids,  so  that  after  their  determina- 
tion 1000  c.  c.  may  be  sure  to  remain. 

c.  The  actual  Analysis. 

Weigh  the  iodine,  best  in  a small  flask,  dissolve  in  the  iodide  of  po- 
tassium solution,  using  about.  5 c.  c.  to  0*1  grm.  of  iodine,  add  hyposul- 


316 


DETERMINATION. 


[§  147. 

phite  solution  from  tlie  burette  till  decoloration  is  just  produced,  then 
3 or  4 c.  c.  starch  solution,  then  iodine  solution  from  a second  burette  to 
incipient  blueness.  The  substance  contains  the  same  amount  of  iodine 
as  the  c.  c.  of  iodine  solution  corresponding  to  the  hyposulphite  used 
minus  the  c.  c.  of  the  former  used  to  destroy  the  excess  of  the  latter. 
Where  the  solutions  are  of  equal  value  and  1 c.  c.  corresponds  to  0-005 
grm.  iodine,  the  calculation  is  in  the  highest  degree  simple ; for  suppose 
we  had  used  21  c.  c.  Na  O,  S2  02  and  1 c.  c.  iodine,  the  quantity  of  iodine 
present  is  0T00  grm. 

21—1=20,  and  20x0-005=0*100. 
d.  Keeping  of  the  Solutions. 

The  iodine  solution  and  the  hyposulphite  solution  are  kept  in  glass- 
stoppered  bottles  in  a cool,  dark  place.  The  former  then  suffers  no 
alteration,  and  the  latter  also  is  stable  or  only  slightly  liable  to  change. 
Caution  demands,  that  the  relation  between  the  two  solutions  should  be 
tested  before  each  new  series  of  experiments.  The  known  amount  of 
iodine  in  the  iodine  solution  is  and  always  remains  the  basis  of  the  pro- 
cess. 


If  a fluid  contains  free  iodine  in  presence  of  iodine  in  a state  of  com- 
bination, the  former  is  determined  in  one  portion,  by  the  preceding 
method,  and  the  total  amount  of  iodine  present  in  another  portion.  To 
this  end,  sulphurous  acid  is  added  until  the  fluid  appears  colorless,  and 
then  solution  of  nitrate  of  silver  (§  145,  I.,  a) ; the  mixture  is  digested 
with  nitric  acid,  to  remove  any  sulphate  of  silver  that  might  have  been 
thrown  down  along  with  the  iodide,  filtered,  &c. ; or  the  fluid  is  distilled 
with  sesquiehloride  of  iron,  as  directed  in  § 145,  I.,  d. 

§ 147. 

4.  Hydrocyanic  Acid. 

I.  Determination. 

a.  If  you  have  free  hydrocyanic  acid  in  solution,  mix  the  solution,  in 
a rather  dilute  state,  with  a solution  of  nitrate  of  silver  in  excess,  add  a 
little  nitric  acid,  allow  to  settle  without  warming,  and  determine  the  pre- 
cipitated cyanide  of  silver  either  by  collecting  on  a weighed  filter,  drying 
at  100°  and  weighing  (§  115,  3),  or  by  collecting  on  an  unweighed  filter 
and  converting  into  metallic  silver.  The  latter  operation  is  performed 
by  igniting  the  precipitate  in  a porcelain  crucible  for  ^ hour,  or  till  it 
ceases  to  lose  weight  (H.  Hose). 

If  you  wish  to  determine  in  this  way  the  hydrocyanic  acid  in  bitter 
almond  water  or  cherry  laurel  water,  add  ammonia  after  the  addition  of 
the  solution  of  nitrate  of  silver  till  the  fluid  has  become  clear,  and  at 
once  supersaturate  slightly  with  nitric  acid.  This  modification  of  the 
process  is  indispensable  to  precipitate  from  these  fluids  the  whole  of  the 
hydrocyanic  acid  as  cyanide  of  silver.  In  measuring  a fluid  containing 
hydrocyanic  acid  with  a pipette,  have  a little  tube  filled  with  granulated 
soda-lime  between  the  latter  and  the  mouth. 

b.  Liebig’s  Volumetric  Method* — If  hydrocyanic  acid  is  mixed  with 


* Anna!,  d.  Chem.  u.  Pharm.  77,  102. 


HYDROCYANIC  ACID. 


317 


§ 147.] 

potassa  to  strong  alkaline  reaction,  and  a dilute  solution  of  nitrate  of 
silver  is  then  added,  a permanent  turbidity  of  cyanide  of  silver — or,  if  a 
few  drops  of  solution  of  chloride  of  sodium  have  been  added  (which  is 
always  advisable),  of  chloride  of  silver — forms  only  after  the  whole  of 
the  cyanogen  is  converted  into  double  cyanide  of  silver  and  potassium.  The 
first  drop  of  solution  of  nitrate  of  silver  added  in  excess  produces  the  per- 
manent precipitate.  1 eq.  silver  consumed  in  the  process  corresponds,  there- 
fore, exactly  to  2 eq.  hydrocyanic  acid  (2  K Cy-f  Ag  0, 1ST 05= Ag  Cy,  K Cy 
+ KO,  N 05).  A decinormal  solution  of  nitrate  of  silver,  containing 
consequently  10*797  grm.  silver  in  the  litre,  should  be  used;  1 c.  c.  of 
this  solution  corresponds  to  0*0054  of  hydrocyanic  acid.  In  examining 
medicinal  hydrocyanic  acid,  5 to  10  grm.  ought  to  be  used,  but  of  bitter 
almond  water  about  50  grm.  ; if  exactly  5*4  or  54  grm.  are  used,  the 
c.  c.  of  the  silver  solution,  divided  by  10,  or  by  100,  expresses  exactly 
the  percentage  of  hydrocyanic  acid.  Medicinal  hydrocyanic  acid  is  suita- 
bly diluted  first  by  adding  from  5 to  8 volumes  of  water ; bitter  almond 
water  also  is  slightly  diluted  ; if  turbid,  alcohol  is  added,  until  the  tur- 
bidity disappears. 

Liebig  has  examined  hydrocyanic  acid  of  various  degrees  of  dilution, 
and  has  obtained  results  by  this  method  corresponding  exactly  with  those 
obtained  by  a.  In  this  method  it  does  not  matter  whether  the  hydro- 
cyanic acid  contains  an  admixture  of  hydrochloric  acid  or  formic  acid. 
A considerable  excess  of  potassa  must  be  avoided. 

If  it  is  intended  to  determine  cyanide  of  potassium  by  this  method,  a 
solution  of  that  salt  must  be  prepared  of  known  strength,  and  a measured 
quantity  used  containing  about  0*1  grm.  of  the  salt.  Should  it  contain 
sulphide'  of  potassium,  a small  quantity  of  freshly  precipitated  carbonate 
of  lead  must  be  first  added,  and  the  solution  filtered  before  proceeding 
to  the  determination. 

II.  Separation  of  Cyanogen  from  the  Metals. 

a.  In  Cyanides  of  the  Alkali  Metals. 

Mix  the  substance  (if  solid,  without  previous  solution  in  water)  with 
excess  of  nitrate  of  silver  solution,  then  add  water,  finally  nitric  acid  in 
slight  excess,  allow  to  settle  without  warming,  and  determine  the  cyanide 
of  silver  as  in  I.,  a.  The  bases  are  determined  in  the  filtrate  after  sepa- 
rating the  excess  of  silver. 

b.  In  Cyanides , which  are  easily  decomposed  by , and  soluble  in , Nitric 
Acid. 

Digest  for  some  time  with  nitrate  of  silver,  stirring  frequently,*  then 
add  nitric  acid  in  moderate  excess,  and  digest  at  a gentle  heat,  till  the 
foreign  cyanide  is  fully  dissolved  and  the  cyanide  of  silver  has  become 
pure  and  quite  white.  Then  filter.  As  a precautionary  measure  it  is 
well  to  test  the  metal  obtained  by  long  ignition  of  the  cyanide  of  silver, 
whether  it  is  free  from  those  metals  which  were  combined  with  the 
cyanogen. 

c.  In  Cyanide  of  Mercury. 

Precipitate  the  aqueous  solution  with  sulphuretted  hydrogen ; the  sul- 
phide of  mercury  may  be  filtered  without  difficulty  if  a little  ammonia 

* Double  cyanide  of  nickel  and  potassium  yields  by  this  process  a mixture  of 
cyanide  of  silver  with  cyanide  of  nickel.  Other  double  cyanides  are  similarly 
decomposed. 


318 


DETERMINATION. 


[§  147. 

I 

or  hydrochloric  acid  be  added;  it  is  determined  according  to  § 118,  3. 
If  the  compound  is  in  the  solid  condition,  the  cyanogen  may  be  deter- 
mined in  another  portion  by  ignition  with  oxide  of  copper,  the  nitrogen 
and  carbonic  acid  being  collected  and  separated  (comp,  organic  analysis). 

H.  Rose  and  Finkener*  give  the  following  method  for  determining 
cyanogen  in  solutions  of  cyanide  of  mercury.  Mix  the  solution  of  the 
cyanide  of  mercury  with  nitrate  of  zinc  dissolved  in  ammonia.  To  1 
part  of  mercury-salt  add  about  2 parts  of  the  zinc-salt.  Add  to  the 
clear  solution  sulphuretted  hydrogen  water  gradually  till  it  produces  a 
perfectly  white  precipitate  of  sulphide  of  zinc.  The  precipitate,  which 
is  a mixture  of  the  sulphides  of  mercury  and  zinc,  settles  well.  After 
a quarter  of  an  hour  filter  it  off  and  wash  with  very  dilute  ammonia. 
The  filtrate  contains  cyanide  of  zinc  dissolved  in  ammonia,  together  with 
nitrate  of  ammonia.  It  does  not  smell  of  hydrocyanic  acid,  and  conse- 
quently no  escape  of  the  latter  takes  place.  Mix  it  with  nitrate  of  sil- 
ver and  then  add  dilute  sulphuric  acid  in  excess.  The  cyanide  of  silver 
is  next  washed  a little  by  decantation,  then — to  free  it  from  any  cyanide 
of  zinc  simultaneously  precipitated — heated  with  a solution  of  nitrate 
of  silver,  finally  filtered  off,  washed,  and  determined  after  I.,  a.  The 
precipitated  sulphides  may  be  dissolved  in  aqua  regia,  and  the  mercury 
precipitated  as  subchloride  according  to  § 118,  2,  a.  The  test-analyses 
communicated  by  Rose  yielded  excellent  results. 

d.  In  compounds  decomposable  by  Oxide  of  Mercury  in  the  Wet  Way. 

Many  simple  cyanides,  and  also  double  cyanides — both  of  the  charac- 
ter of  the  double  cyanide  of  nickel  and  potassium,  and  of  the  ferro-  or 
ferricyanides  (not,  however,  cobalticyanides) — may,  as  is  well  known,  be 
completely  decomposed  by  boiling  with  excess  of  oxide  of  mercury  and 
water,  all  cyanogen  being  obtained  as  cyanide  of  mercury,  and  the  metals 
passing  into  oxides. 

H.  Rose  ( loc . cit.)  has  shown,  that  Prussian  blue,  ferro-  and  ferri- 
cyanide  of  potassium,  more  particularly,  may  be  readily  analyzed  in 
this  manner. 

Boil  a few  minutes  with  water  and  excess  of  oxide  of  mercury  till  com- 
plete decomposition  is  effected,  add — in  order  to  render  the  sesquioxide 
of  iron  and  oxide  of  mercury  removable  by  the  filter — nitric  acid  in 
small  portions,  till  the  alkaline  reaction  has  nearly  disappeared,  filter, 
wash  with  hot  water,  dry  the  precipitate,  ignite — very  gradually  raising 
the  heat — under  a hood  (with  a good  draught),  and  weigh  the  sesqui- 
oxide of  iron  remaining.  In  the  filtrate  the  cyanogen  is  determined 
according  to  c,  and  any  potassa  that  may  be  present  is  estimated  in  the 
fluid  filtered  from  the  cyanide  of  silver. 

e.  Determination  o f Metals  contained  in  Cyanides  with  decomposition 
and  volatilization  of  the  Cyanogen. 

Of  the  various  means  for  completely  decomposing  compounds  of  cyan- 
ogen, especially  also  the  double  cyanides,  according  to  H.  Rose  {loc.  cit.)f 
three  particularly  are  worthy  of  recommendation,  viz.,  concentrated 
sulphuric  acid,  sulphate  of  mercury,  and  chloride  of  ammonium.  The 
nitrates  seemed  decidedly  less  suitable  on  account  of  their  too  violent 
action. 

a.  Decomposition  by  Sulphuric  Acid.  All  cyanogen  compounds, 


* Zeitschr.  f.  anal.  Chem.  1,  288. 


HYDROCYANIC  ACID. 


319 


§147.] 

simple  or  double,  are  completely  decomposed  and  converted  into  sul- 
phates or  oxides,  as  the  case  may  be,  if  treated  in  a powdered  condition 
in  a platinum  dish  or  a capacious  platinum  crucible  with  a mixture  of 
about  3 parts  concentrated  sulphuric  acid  and  1 part  water,  and  heated 
till  almost  all  the  sulphuric  acid  has  been  expelled.  The  residual  mass 
is  then  free  from  cyanogen.  It  is  dissolved  in  water,  if  necessary,  with 
addition  of  hydrochloric  acid,  and  the  oxides  determined  by  the  usual 
methods. 

j3.  Decomposition  by  Sulphate  of  Mercury.  Of  the  combinations 
of  oxide  of  mercury  with  sulphuric  acid,  those  suitable  to  our  present 
purpose  are  the  neutral  and  the  basic  (Turpeth  mineral).  The  substance 
is  mixed  with  6 parts  of  the  latter,  heated  in  a platinum  crucible  gradu- 
ally, and  finally  maintained  for  a long  time  at  a red-heat,  till  all  the 
mercury  has  volatilized,  and  the  weight  of  the  crucible  remains  constant. 
If  alkalies  are  present,  a little  carbonate  of  ammonia  is  added  during 
the  final  ignition,  from  time  to  time,  in  order  to  convert  the  bisulphates 
into  neutral  salts.  The  residue  may  usually  be  analyzed  by  simple  treat- 
ment with  water,  in  the  case  of  ferrocyanide  of  potassium,  for  instance, 
the  sulphate  of  potassa  dissolves,  and  pure  (alkali-free)  sesquioxide  of 
iron  remains  behind.  The  test-analyses  that  have  been  communicated 
yielded  excellent  results. 

y.  Decomposition  by  Chloride  of  Ammonium.  Mix  the  substance 
with  twice  or  thrice  the  amount  of  this  salt  and  ignite  the  mixture 
moderately  in  a stream  of  hydrogen  (apparatus,  p.  181,  fig.  47).  From 
the  cooled  mass  water  extracts  alkaline  metallic  chloride,  while  the 
reducible  metals  remain  behind  in  the  metallic  state.  The  method  is 
peculiarly  adapted  for  the  analysis  of  double  cyanide  of  nickel  and  po- 
tassium and  cobalticyanide  of  potassium,  not  so  for  iron  compounds, 
since  the  iron  obtained  is  not  pure,  but  contains  carbon. 

If  one  of  the  methods  described  in  e is  employed,  the  nitrogen  and 
carbon  (the  cyanogen)  must  be  determined  by  combustion,  if  an  estima- 
tion by  the  loss  is  not  sufficient. 

f.  Determination  of  the  Alkalies , especially  of  Ammonia  in  Soluble 
Ferrocyanides. 

Mix  the  boiling  solution  with  a solution  of  chloride  of  copper  in 
moderate  excess,  filter  off  the  precipitated  ferrocyanide  of  copper,  free 
the  filtrate  from  copper  by  means  of  sulphuretted  hydrogen,  and  then 
determine  the  alkalies  (Reindel*). 

g.  Volumetric  Determination  of  Ferro-  and  Ferricyanogen. 

a.  After  E.  de  Haen.  This  method,  devised  in  my  laboratory,  is 
founded  upon  the  simple  fact  that  a solution  of  ferrocyanide  of  potassium 
acidified  with  sulphuric  acid  or  with  hydrochloric  acid  (and  which  may 
accordingly  be  assumed  to  contain  free  hydroferrocyanic  acid),  is  by 
addition  of  permanganate  of  potassa  converted  into  the  corresponding 
ferricyanide.  If  this  conversion  is  effected  in  a very  dilute  fluid,  con- 
taining about  0*2  grm.  ferrocyanide  of  potassium  in  from  200  to  300  c. 
c.,  the  termination  of  the  reaction  is  clearly  and  unmistakably  indicated 
by  the  change  of  the  originally  pure  yellow  color  of  the  fluid  to  reddish- 
yellow. 

The  process  requires  two  test  fluids  of  known  strength,  viz., 


* Joum.  f.  prakt.  Chem.  65,  452. 


320 


DETERMINATION. 


[§  147. 


1.  A solution  of  pure  ferrocyanide  of  potassium. 

2.  A solution  of  permanganate  of  potassa. 

The  former  is  prepared  by  dissolving  20  grm.  perfectly  pure  and  dry 
crystallized  ferrocyanide  of  potassium  in  water  to  1 litre;  each  c.  c. 
therefore  contains  20  mgrm.  The  latter  is  diluted  so  that  somewhat 
less  than  a buretteful  is  required  for  10  c.  c.  of  the  solution  of  ferro* 
cyanide  of  potassium. 

To  determine  the  strength  of  the  permanganate  of  potassa  solution  in 
its  action  upon  ferrocyanide  of  potassium,  measure  off',  by  means  of  a 
small  pipette,  10  c.  c.  of  the  solution  of  ferrocyanide  of  potassium  (con- 
taining 0*200  grm.)  dilute  with  about  250  c.  c.  water,  acidify  with  hydro- 
chloric acid,  place  the  glass  on  a sheet  of  white  paper,  and  allow  the 
permanganate  to  drop  into  the  fluid,  stirring  it  at  the  same  time,  until 
the  change  from  yellow  to  reddish-ye llow  indicates  that  the  conversion 
is  complete.*  Repetitions  of  the  experiment  always  give  very  accu- 
rately corresponding  results.  If  at  any  time  you  have  reason  to  suspect 
that  the  permanganate  has  suffered  alteration,  recourse  must  be  had 
again  to  this  experiment. 

To  determine  the  amount  of  real  ferrocyanide  of  potassium  contained 
in  any  given  sample  of  the  commercial  article,  dissolve  5 grm.  to  250 
c.  c. ; take  10  c.  c.  of  this  solution,  and  examine  as  just  directed.  Sup- 
pose, in  determining  the  strength  of  the  permanganate,  you  have  used 
20  c.  c.,  and  you  find  now  that  19  c.  c.  is  sufficient,  the  simple  rule-of- 
three  sum, 

20  : 0*200::  19  : a: 

will  inform  you  how  much  pure  ferrocyanide  of  potassium  0*200  grin, 
of  the  analyzed  salt  contains.  And  even  this  small  calculation  may  be 
dispensed  with,  by  diluting  the  permanganate  so  that  exactly  50  c.  c. 
correspond  to  0*200  of  ferrocyanide  of  potassium,  as,  in  that  case,  the 
number  of  half-c.  c.  consumed  expresses  directly  the  percentage  of  the 
ferrocyanide  of  potassium  present  in  the  analyzed  salt. 

Instead  of  determining  the  strength  of  the  permanganate  by  means 
of  pure  ferrocyanide  of  potassium,  which  is  unquestionably  the  best  way, 
one  of  the  methods  given  in  § 112,  2,  may  also  be  employed;  bearing 
in  mind,  in  that  case,  that  2 eq.  ferrocyanide  of  potassium  = 422*44 
(together  with  the  water  of  crystallization),  2 eq.  iron  dissolved  to  pro- 
toxide = 56,  and  1 eq.  oxalic  acid  = 63  (together  with  the  water  of 
hydration  and  crystallization)  are  equivalent  in  their  action  upon  solu- 
tion of  permanganate  of  potassa. 

The  analysis  of  soluble  ferricyanides  by  this  method  is  effected  by 
reducing  them  to  ferrocyanides,  acidifying,  and  then  proceeding  in  the 
same  way  as  just  now  described.  The  reduction  is  effected  as  follows: — 
Mix  the  weighed  ferricyanide  with  solution  of  soda  or  potassa  in  excess, 
boil,  and  add  concentrated  solution  of  sulphate  of  protoxide  of  iron 
gradually,  and  in  small  portions,  until  the  color  of  the  precipitate  appears 
black,  which  is  a sign  that  protosesquioxide  of  iron  has  precipitated. 
Dilute  now  to  300  c.  c.,  mix,  filter,  and  proceed  to  determine  the  ferro- 
cyanide in  portions  of  50  or  100  c.  c.  of  the  fluid.  As  the  space  occu- 
pied by  the  precipitate  is  not  taken  into  account  in  this  process,  the 

* If  you  wish  at  first  for  some  additional  evidence  besides  the  change  of  color, 
add  to  a drop  of  the  mixture  on  a plate,  a drop  of  solution  of  sesquichloride  of 
iron : if  this  fails  to  produce  a blue  tint,  the  conversion  is  accomplished. 


HYDROSULPHURIC  ACID. 


321 


§ 148.] 

results  are  not  absolutely  accurate.  The  difference  is  so  very  trifling, 
however,  that  it  may  safely  be  disregarded. 

Insoluble  ferro-  or  ferricyanides,  decomposable  by  boiling  solution  of 
potassa  (as  are  most  of  these  compounds),  are  analyzed  by  boiling  a weighed 
sample  sufficiently  long  with  an  excess  of  solution  of  potassa  (adding,  in 
the  case  of  ferricyanides,  sulphate  of  protoxide  of  iron),  and  then  pro- 
ceeding in  the  same  way  as  directed  above. 

f3.  After  E.  Bohlig.* 

In  the  case  of  a fluid  containing  ferrocyanide  of  potassium,  and  also 
sulphocyanide  (for  instance,  the  red  liquor  of  the  prussiate  works),  the 
method  given  in  a cannot  be  employed,  as  the  hydrosulphocyanic  acid 
also  reduces  permanganic  acid.  The  following  method — depending  on 
the  precipitation  of  the  ferrocyanogen  with  solution  of  sulphate  of  copper 
— may  then  be  used ; , it  is  accurate  enough  for  technical  purposes.  Dis- 
solve 10  grm.  pure  sulphate  of  copper  to  1 litre,  also  4 grm.  pure  dry 
ferrocyanide  of  potassium  to  1 litre.  Add  to  50  c.  c.  of  the  latter  solution 
(which  contain  0*2  grm.  ferrocyanide  of  potassium)  copper  solution  from 
a burette  to  complete  precipitation  of  the  ferrocyanogen.  In  order  to  hit 
this  point  exactly,  from  time  to  time  dip  a strip  of  filter-paper  into  the 
brownish-red  fluid,  which  will  imbibe  the  clear  filtrate,  leaving  the  preci- 
pitate of  ferrocyanide  of  copper  behind.  At  first  the  moist  strips  of  paper, 
when  touched  with  sesquichloride  of  iron,  become  dark  blue,  the  reaction 
gradually  gets  weaker  and  weaker,  and  finally  vanishes  altogether.  We 
now  know  the  value  of  the  copper  solution  with  reference  to  its  action  on 
ferrocyanide  of  potassium,  and  can,  therefore,  by  its  means  test  solutions 
containing  unknown  amounts  of  ferrocyanogen.  If  alkaline  metallic  sul- 
phides are  present,  they  are  first  removed  by  boiling  with  carbonate  of 
lead.  After  filtering  off  the  sulphide  of  lead,  acidify  with  dilute  sulphu- 
ric acid,  and  then  proceed. 

§ 148. 

5.-  Hydrosulphuric  Acid. 

I.  Determination. 

Sulphuretted  hydrogen  in  the  free  state  is  most  readily  and  very  accu- 
rately determined  by  volumetric  analysis,  by  means  of  iodine;  it  may  also 
be  determined  by  conversion  into  a suitable  sulphide  or  into  sulphate  of 
baryta,  and  weighing. 

a.  The  method  of  determining  free  sulphuretted  hydrogen  by  volu- 
metric analysis,  by  means  of  a solution  of  iodine,  was  employed  first  by 
Dupasquier.  That  chemist  used  alcoholic  solution  of  iodine  for  the  pur- 
pose. But  as  the  action  of'  the  iodine  upon  the  alcohol  gradually 
alters  the  composition  of  this  solution,  it  is  better  to  use  a solution  of 
iodine  in  iodide  of  potassium.  The  decomposition  is  as  follows : 

H S-f  I = H I + S 

1 eq.  1=127  corresponds,  therefore^  to  1 eq.  H S = 17.  However,  this 
exact  decomposition  can  be  relied  upon  with  certainty  only  if  the  amount 
of  sulphuretted  hydrogen  in  the  fluid  to  be  analyzed  does  not  exceed  004 
per  cent.  (Bunsen).  Fluids  containing  a larger  proportion  of  sulphuretted 


Polytechn.  Notizhlatt,  tfi,  81. 
21 


DETERMINATION. 


322 


[§  148. 


hydrogen  must  therefore  first  be  diluted  to  the  required  degree  with  boiled 
water  cooled  out  of  the  contact  of  air. 

The  iodine  solution  of  § 146  may  be  used  for  the  estimation  of  larger 
quantities  of  sulphuretted  hydrogen ; for  weak  solutions,  e.  g.,  sulphuretted 
mineral  water,  it  is  advisable  to  dilute  the  iodine  solution  of  § 146  to 
5 times  the  volume,  which  accordingly  will  give  a fluid  containing  about 
0* * * §001  grm.  iodine  in  the  c.  c. 

The  process  is  conducted  as  follows : — 

Measure  or  weigh  a certain  quantity  of  the  sulphuretted  water,  dilute, 
if  required,  in  the  manner  directed,  add  some  thin  starch-paste,  and  then 
solution  of  iodine,  with  constant  shaking  or  stirring,  until  the  permanent 
blue  color  begins  to  appear.  The  result  of  this  experiment  indicates  ap- 
proximately, but  not  witli  positive  accuracy,  the  relation  between  the 
examined  water  and  the  iodine  solution.  Suppose  you  have  consumed,  to 
220  c.  c.  of  the  sulphuretted  water,  12  c.  c.  of  a solution  of  iodine  con- 
taining 0*0009 18  grm.  iodine  in  the  c.  c.*  Introduce  now  into  a flask  nearly 
the  quantity  of  iodine  solution  required,  add  the  sulphuretted  water  in 
quantity  either  already  determined,  or  to  be  determined,  by  weight  oi 
measure ; f then  to  the  colorless  fluid  add  thin  starch-paste,  and  after  this 
iodine  solution  until  the  blue  color  just  begins  to  show.  By  this  course 
of  proceeding,  you  avoid  the  loss  of  sulphuretted  hydrogen  which  would 
otherwise  be  caused  by  evaporation  and  oxidation.  In  my  analysis  of 
the  Weilbach  water,  256  c.  c.  of  the  water  required,  in  my  second  experi- 
ment, 16*26  c.  c.  of  iodine  solution,  which,  calculated  to  the  quantity  of 
sulphuretted  water  used  in  the  first  experiment,  viz.,  220  c.  c.,  makes  13*9 
c.  c.,  or  T9  c.  c.  more. 

But  even  now  the  experiment  cannot  yet  be  considered  quite  conclu- 
sive, when  made  with  a solution  of  iodine  so  dilute ; it  being  still  necessary 
to  ascertain  how  much  iodine  solution  is  required  to  impart  the  same  blue 
tint  to  the  same  quantity  of  ordinary  water  mixed  with  starch-paste,  of  the 
same  temperature,  J and  as  nearly  as  possible  in  the  same  condition  § as 
the  analyzed  sulphuretted  water,  and  to  deduct  this  from  the  quantity  of 
iodine  solution  used  in  the  second  experiment.  Thus,  in  the  case  men- 
tioned, I had  to  deduct  0*5  c.  c.  from  the  16*26  c.  c.  used.  If  the  in- 
structions here  given  are  strictly  followed,  this  method  gives  very  accurate 
results  (see  Expt.  No.  91). 

b.  Mix  the  sulphuretted  fluid  with  an  excess  of  solution  of  arsenite  of 
soda,  add  hydrochloric  acid,  allow  to  deposit,  and  determine  the  sul- 
phide of  arsenic  as  directed  § 127.  If  the  quantity  of  sulphuretted  hydro- 
gen in  the  analyzed  fluid  is  moderately  large,  the  results  obtained  by  this 
method  are  accurate  (compare  Expt.  No.  91);  but  in  the  case  of  very 
dilute  solutions  the  results  are  too  low,  as  a little  tersulphide  of  arsenic 
remains  in  solution.  Hence,  in  my  analysis  of  the  Weilbach  water,  this 
method  gave  only  0*006621  and  0*006604  per  1000,  whilst  water  taken 
from  the  well  at  the  same  time,  and  determined  with  iodine,  gave  0*007025 
of  H S per  1000.  Instead  of  arsenious  acid,  solution  of  chloride  of  copper 


* The  numbers  here  stated  are  those  which  I obtained  in  the  analysis  of  the 
Weilbach  water, 

f Compare  Experiment  No.  91. 

X Annal.  d.  Chem.  u.  Pharm. , 102, 186. 

§ I would  recommend,  in  cases  where  the  sulphuretted  water  contains  bicar- 
bonate of  soda,  to  add  to  the  ordinary  water  an  equal  quantity  of  this  salt,  as  its 
presence  has  a -slight  influence  on  the  appearance  of  the  final  reaction. 


HYDROSULPHURIC  ACID. 


323 


§ 148.] 

or  a solution  of  silver  may  be  employed  as  precipitant,  and  the  sulphur 
determined  in  the  sulphide  of  copper  as  sulphate  of  baryta  (see  II.),  or 
in  the  sulphide  of  silver  as  chloride  of  silver.  The  results  obtained  by 
precipitating  with  chloride  of  copper  are  also  too  low,  in  the  case  of  very 
dilute  iluids. 

For  the  analysis  of  mineral  waters,  the  method  a will  always  answer 
best,  unless  presence  of  hyposulphites  should  impair  its  accuracy. 

c.  If  the  sulphuretted  hydrogen  is  evolved  in  the  gaseous  state,  and  large 
quantities  are  to  be  determined,  the  best  way  is  to  conduct  it  first  through 
several  bulbed  U-tubes  (fig.  59,  p.  308),  containing  an  alkaline  solution 
of  arsenite  of  soda,  then  through  a tube  connected  with  the  exit  of  the  last 
U-tube,  which  contains  pieces  of  glass  moistened  with  solution  of  soda ; to 
mix  the  fluids  afterwards,  and  proceed  as  in  b or  c.  If,  on  the  other  hand, 
we  have  to  determine  small  quantities  of  sulphuretted  hydrogen  contained  in 
a large  amount  of  air,  &c.,  it  is  well  to  pass  the  gaseous  mixture  in  question 
in  separate  small  bubbles  through  a very  dilute  solution  of  iodine  in  iodide 
of  potassium,  of  known  volume  and  strength,  which  is  contained  in  a long 
glass  tube  fixed  in  an  inclined  position  and  protected  against  sunlight. 
The  free  iodine  remaining  is  finally  estimated  by  means  of  a solution  of 
hyposulphite  of  soda  (§  146) ; the  difference  gives  us  the  quantity  of  iodine 
which  has  been  converted  by  sulphuretted  hydrogen  into  hydriodic  acid, 
and  consequently  corresponds  to  the  amount  of  the  sulphuretted  hydrogen 
present.  The  volume  of  the  gaseous  mixture  may  be  known  by  measuring 
the  water  which  has  escaped  from  the  aspirator  used.  The  arrangement 
of  the  absorption  tube  is  the  same  as  is  figured  in  connection  with  the  de- 
termination of  carbonic  acid  in  the  air  (§  241,  at  the  end).  The  thin 
glass  tube  conducting  the  gas  into  the  absorption  tube,  however,  must 
not  be  provided  with  an  india-rubber  elongation. 

II.  Separation  and  Determination  of  Sulphur  in  Sulphides . 

A.  Methods  based  on  the  Conversion  of  the  Sulphur  into 
Sulphuric  Acid. 

1.  Methods  in  the  Dry  Way. 

a.  Oxidation  by  Alkaline  Nitrates  (applicable  to  all  compounds  of  sul- 
phur). If  the  sulphides  do  not  lose  any  sulphur  on  heating,  mix  the  pulver- 
ized and  weighed  substance  with  3 parts  of  anhydrous  carbonate  of  soda  and 
4 of  nitrate  of  potassa,  with  the  aid  of  a rounded  glass  rod,  wipe  the  particles 
of  the  mixture  which  adhere  to  the  rod  carefully  off  against  somp  carbonate 
of  soda,  and  add  this  to  the  mixture.  Heat  in  a platinum  or  porcelain 
crucible  (which,  however,  is  somewhat  affected  by  the  process),  at  a 
gradually  increased  temperature  to  fusion ; keep  the  mass  in  that  state  for 
some  time,  then  allow  it  to  cool,  heat  the  residue  with  water,  filter,  and 
determine  in  the  filtrate,  which  contains  the  whole  of  the  sulphur  as  alka- 
line sulphate,  the  sulphuric  acid  as  directed  in  § 132.  The  metal,  metallic 
oxide,  or  carbonate,  which  remains  undissolved,  is  determined,  according 
to  circumstances,  either  by  direct  weighing  or  in  some  other  suitable  way. 
In  the  presence  of  lead,  before  filtering,  pass  carbonic  acid  through  the 
solution  of  the  fused  mass,  to  precipitate  the  small  quantity  of  that  metal 
which  has  passed  into  the  alkaline  solution, 

Should  the  sulphides,  on  the  contrary,  lose  sulphur  on  heating,  the  finely 
powdered  compound  is  mixed  with  4 parts  carbonate  of  soda,  8 parts 


DETERMINATION. 


324 


[§  148. 


nitre,  and  24  parts  pure  and  perfectly  dry  chloride  of  sodium,  and  the 
process  otherwise  conducted  as  already  given. 

b.  Oxidation  by  Chlorine  Gas  (after  Berzelius  and  H.  Bose,  especially 
suitable  for  sulphosalts  of  complicated  composition). 

The  following  apparatus,  or  one  of  similar  construction,  is  used  : — 


Fig.  60. 


A is  the  evolution  flask,*  J3  contains  concentrated  sulphuric  acid,  C 
chloride  of  calcium,  D the  substance,  JE  is  the  receiver  containing  water 
(or — in  the  presence  of  antimony — a solution  of  tartaric  acid  in  dilute 
hydrochloric  acid),  J^is  a TJ-tube  also  containing  water,  G conducts  the 
escaping  chlorine  into  a carboy  filled  with  moist  hydrate  of  lime. 

When  the  apparatus  is  arranged,  the  sulphide  to  be  examined  is  weighed 
in  a narrow  glass  tube  sealed  at  one  end,  and  subsequently  cautiously 
transferred  from  this  tube  to  the  bulb,  in  the  manner  illustrated  by 
fig.  61,  so  as  to  prevent  any  portion  of  the 
substance  getting  into  the  ends  of  the  bulb- 
tube. 

[In  most  cases  it  is  more  convenient  to  put 
the  weighed  substance  into  a porcelain  tray 
(fig.  24),  which  is  slipped  into  a plain  piece  of 
Bohemian  combustion-tube  bent  like  D 0.  At 
the  close  of  the  process  the  tray  may  be  with- 
drawn and  its  contents  weighed  or  otherwise 
treated.] 

When  the  apparatus  is  filled  with  chlorine,  D is  connected  with  C, 
and  the  chlorine  is  allowed  to  act  on  the  sulphide,  at  first  without  the 


* Pour  a perfectly  cold  mixture  of  45  parts  of  sulphuric  acid  and  21  of  water,  over 
one  of  18  parts  of  chloride  of  sodium  and  15  of  finely  powdered  binoxide  yf  manga- 
nese, and  shake,  when  a steady  evolution  of  chlorine  will  at  once  begin,  which, 
when  it  shows  signs  of  slackening,  may  be  promoted  by  a gentle  heat. 


§ US.] 


HYDROSULPIIURIC  ACID. 


325 


aid  of  heat.  When  no  further  alteration  is  observed — the  receiver  E 
being  full  of  chlorine — a very  gentle  heat  is  applied  to  the  bulb,  care 
being  taken  also  to  keep  the  tube  0 warm,  securing  it  thus  from  being 
stopped  up  by  the  sublimate  of  a volatile  chloride.  The  sulphide  is  com- 
pletely decomposed  by  the  chlorine,  the  metals  being  converted  into  chlo- 
rides, which  partly  remain  in  the  bulb,  partly — (viz.  the  volatile  ones,  as 
chloride  of  antimony,  chloride  of  arsenic,  chloride  of  mercury) — pass  over 
into  the  receiver  ; the  sulphur  combines  with  the  chlorine  to  chloride  of 
sulphur,  which  passes  over  into  E , where,  coming  in  contact  with  water, 
it  decomposes  with  the  latter,  forming  hydrochloric  acid  and  hypo- 
sulphurous  acid,  with  separation  of  sulphur.  The  hyposulphurous  acid 
decomposes  again  into  sulphur  and  sulphurous  acid,  which  latter  is  at  last, 
by  the  action  of  the  chlorine  water  in  E,  converted  into  sulphuric  acid. 
The  final  result  of  the  decomposition  is  consequently  sulphuric  acid  and  a 
greater  or  less  amount  of  separated  sulphur.  The  operation  is  concluded 
when  no  more  products — with  the  exception,  perhaps,  of  sesquichloride 
of  iron,  the  complete  expulsion  of  which  need  not  be  awaited — p ass  over 
from  the  bulb.  Heat  is  then  applied  to  the  bulb-tube,  proceeding  from 
the  bulb  towards  the  bend,  so  as  to  force  all  the  chloride  of  sulphur 
and  the  volatile  metallic  chlorides  to  pass  over  into  E,  or  at  least  to  oc- 
cupy the  end  of  the  bulb-tube. 

The  apparatus  is  left  undisturbed  a short  time  longer,  after  which  the 
tube  is  cut  off  under  the  bend  at  <9,  and  the  separate  end,  which  generally 
contains  a portion  of  the  volatile  chlorides,  closed  by  inverting  over  it  a 
glass  tube  sealed  at  one  end  and  moistened  inside.  [In  case  a porcelain 
tray  has  been  used,  this  is  withdrawn  and  the  entire  tube  is  subjected  to 
the  following  treatment.]  The  tube  is  now  allowed  to  stand  24  hours,  to 
allow  the  volatile  chlorides  to  absorb  moisture,  which  will  render  them  solu- 
ble in  water  without  generating  heat.  The  metallic  chlorides  in  the  cut-off 
end  of  the  tube  (or  tray)  are  then  dissolved  in  dilute  hydrochloric  acid, 
the  end  (or  tray)  is  rinsed,  and  the  solution  added  to  the  contents  of  the 
tubes  E and  E / a very  gentle  heat  is  now  applied  until  the  free  chlorine 
is  expelled,  and  the  fluid  is  then  allowed  to  stand  until  the  sulphur  has 
solidified.  The  sulphur  is  filtered  off  on  a weighed  filter,  washed,  dried, 
and  weighed.  The  filtrate  is  precipitated  with  chloride  of  barium  (§  132), 
by  which  operation  the  amount  of  that  portion  of  the  sulphur  is  determin- 
ed which  has  been  converted  into  sulphuric  acid.  The  fluid  filtered  from 
the  sulphate  of  baryta  contains,  besides  the  excess  of  chloride  of  barium 
added,  also  the  volatile  metallic  chlorides ; which  latter  are  finally  deter- 
mined in  it  by  the  proper  methods,  which  will  be  found  in  Section  Y. 

The  chloride  remaining  in  the  bulb-tube  is  either  at  once  weighed  as 
such  (chloride  of  silver,  chloride  of  lead),  or  where  this  is  impracticable — 
as  in  the  case  of  copper,  for  instance,  which  remains  partly  as  subchloride, 
partly  as  chloride — it  is  dissolved  in  water,  hydrochloric  acid,  nitrohydro- 
chloric  acid,  or  some  other  suitable  solvent,  and  the  metal  or  metals  in  the 
solution  are  determined  by  the  methods  already  described,  or  which  will 
be  found  in  Section  Y.  To  be  enabled  to  ascertain  the  weight  of  the 
bulb-tube  containing  the  chloride  of  silver  or  chloride  of  lead,  it  is  advisa- 
ble to  reduce  the  chlorides  by  hydrogen  gas,  and  then  dissolve  the  metals 
in  nitric  acid. 

c.  Oxidation  by  Oxide  of  Mercury  ( after  Bunsen). 

This  method,  which  will  be  found  in  detail  under  “ the  determination 


326 


DETERMINATION. 


[§  148. 


of  sulphur  in  organic  bodies”  (§  186,  a , 4),  is  particularly  suited  to  the 
estimation  of  sulphur  in  volatile  compounds,  or  in  substances  which 
when  heated  lose  sulphur. 

2.  Methods  in  the  T Vet  Way. 

a.  Oxidation  of  the  Sulphur  by  Acids  yielding  Oxygen  A 

a.  Weigh  the  finely  pulverized  sulphide  in  a small  glass  tube  sealed 
at  one  end,  and  drop  the  tube  into  a tolerably  capacious  strong  bottle 
with  glass  stopper,  which  contains  red  fuming  nitric  acid  (perfectly  free 
from  sulphuric  acid)  in  more  than  sufficient  quantity  to  effect  the  decom- 
position of  the  sulphide.  Immediately  after  having  dropped  in  the  tube, 
close  the  bottle.  When  the  action,  which  is  very  impetuous  at  first, has 
somewhat  abated,  shake  the  bottle  a little ; as  soon  as  this  operation 
ceases  to  cause  renewed  reaction,  and  the  fumes  in  the  flask  have  con- 
densed, take  out  the  stopper,  rinse  this  with  a little  nitric  acid,  letting 
the  rinsings  run  into  the  bottle,  and  then  heat  the  latter  gently. 

aa.  The  whole  of  the  Sulphur  has  been  oxidized , the  Fluid  is  perfectly 
clear,  f 

Dilute  with  much  water,  and  determine  the  sulphuric  acid  formed  as 
directed  in  § 132.  Do  not  neglect  to  wash  the  precipitate  thoroughly 
with  hot  water,  and  to  ascertain,  after  weighing,  whether  it  is  absolute- 
ly insoluble  in  dilute  hydrochloric  acid.  Separate  the  bases  in  the  fil- 
trate from  the  excess  of  the  salt  of  baryta  by  the  proper  methods,  which 
will  be  found  in  Section  \.  If  any  considerable  amount  of  nitric  acid 
has  been  used,  evaporate  the  excess  of  the  same  after  addition  of  some 
nitrate  of  potassa,  before  precipitating  the  sulphuric  acid. 

bb.  Undissolved  Sulphur  floats  in  the  fluid. 

Add  chlorate  of  potassa  in  small  portions,  or  strong  hydrochloric 
acid,  and  digest  some  time  on  a water  bath.  This  process  will  often  suc- 
ceed in  dissolving  the  whole  of  the  sulphur.  Should  this  not  be  the 
case,  and  the  undissolved  sulphur  appear  of  a pure  yellow  color,  dilute 
with  water,  collect  on  a weighed  filter,  wash  carefully,  dry,  and  weigh. 
After  weighing,  ignite  the  whole,  or  a portion  of  it,  to  ascertain  whether 
it  is  perfectly  pure.  If  a fixed  residue  remains  (consisting  commonly 
of  quartz,  gangue,  &c.,  but  possibly  also  of  sulphate  of  lead,  sulphate  of 
baryta,  &c.),  deduct  its  weight  from  that  of  the  impure  sulphur.  In  the 
filtered  fluid  determine  the  sulphuric  acid  as  in  aay  calculate  the  sulphur 
in  it,  and  add  the  amount  to  that  of  the  undissolved  sulphur.  If  the 
residue  left  upon  the  ignition  of  the  undissolved  sulphur  contains  an  in- 
soluble sulphate,  decompose  this  as  directed  in  § 132,  and  add  the  sul- 
phur found  in  it  to  the  principal  amount. 

In  the  presence  of  bismuth,  the  addition  of  chlorate  of  potassa  or  of 
hydrochloric  acid  is  not  advisable,  as  chlorine  interferes  with  the  deter- 
mination of  bismuth. 

j3.  Mix  the  finely  pulverized  metallic  sulphide,  in  a dry  flask,  by  shak- 
ing, with  powdered  chlorate  of  potassa  (free  from  sulphuric  acid),  and  add 


* In  presence  of  lead,  baryta,  strontia,  lime,  tin,  and  antimony,  method  b is 
preferable  to  a. 

\ This  can  of  course  be  the  case  only  in  absence  of  metals  forming1  insoluble 
salts  with  sulphuric  acid.  If  such  metals  are  present,  proceed  as  in  bb , as  it  is 
in  that  case  less  easy  to  judge  whether  complete  oxidation  of  the  sulphur  has 
beeu  attained. 


HYDROSULPHURIC  ACID. 


327 


§ 148.] 

moderately  concentrated  hydrochloric  acid  in  small  portions.  Cover  the 
flask  with  a watch-glass,  or  with  an  inverted  small  flask.  When  the 
whole  of  the  chlorate  of  potassa  is  decomposed,  heat  gently,  finally  on  the 
water-bath,  until  the  fluid  smells  no  longer  of  chlorine.  Proceed  now  as 
directed  in  a,  aa,  or  bb  according  to  whether  the  sulphur  is  completely 
dissolved  or  not.  In  the  latter  case  you  must  of  course  immediately  di- 
lute and  filter.  The  oxidation  of  the  sulphur  may  be  effected  also  by  heat- 
ing with  ordinary  nitric  acid  and  chlorate  of  potassa. 

y.  Strong  nitrohydrochloric  acid  is  also  often  used  instead  of  the  oxi- 
dizing agents  named  in  a and  3 ; however,  with  this  the  complete  con- 
version of  the  sulphur  into  sulphuric  acid  succeeds  more  rarely. 

b.  Oxidation  of  the  Sulphur  by  Chlorine  in  Alkaline  Solution  ( after 
Pivot,  Beudant,  and  Daguin.  Suitable  also  for  determining  the  sul- 
phur in  the  crude  article*). 

Heat  the  very  finely  pulverized  sulphide  or  crude  sulphur,  for  several 
hours  with  solution  of  potassa,  free  from  sulphuric  acid  (which  dissolves 
free  sulphur,  as  well  as  the  sulphides  of  arsenic  and  antimony),  and  then 
conduct  chlorine  into  the  fluid.  This  speedily  oxidizes  the  sulphur ; the 
sulphuric  acid  formed  combines  with  the  potassa  to  sulphate,  which  dis- 
solves in  the  fluid,  whilst  the  metals  converted  into  oxides  remain  undis- 
solved. Filter,  acidify  the  alkaline  filtrate,  and  precipitate  the  sulphuric 
acid  from  it  by  chloride  of  barium  (§  132).  Arsenic  and  antimony  pass 
into  the  alkaline  solution  in  the  form  of  acids,  but  not  so  lead,  which  is 
converted  into  binoxide,  and  remains  completely  undissolved.  This 
method  is,  therefore,  particularly  suitable  in  presence  of  sulphide  of 
lead.  In  presence  of  sulphide  of  iron,  sulphate  of  potassa  is  formed  at 
first,  and  hydrate  of  sesquioxide  of  iron,  which,  if  the  action  of  the 
chlorine  is  allowed  to  continue,  will  be  converted  into  ferrate  of  potassa. 
As  soon,  therefore,  as  the  fluid  commences  to  acquire  a red  tint,  the 
transmission  of  chlorine  must  be  discontinued,  and  the  fluid  gently 
heated  for  a few  moments  with  powdered  quartz,  to  decompose  the  ferric 
acid. 

It  occasionally  happens,  more  particularly  in  presence  of  sand,  iron 
pyrites,  oxide  of  copper,  &c.,  that  the  process  is  attended  with  impetu- 
ous disengagement  of  oxygen,  which  almost  completely  prevents  the 
oxidizing  action  of  the  chlorine.  However,  this  accident  may  be  guarded 
against  by  reducing  the  substances  to  be  analyzed  to  the  very  finest  pow- 
der. 

J3.  Methods  Based  on  the  Conversion  of  the  Sulphur  into 
Sulphuretted  Hydrogen  or  a Metallic  Sulphide. 

a.  The  determination  of  the  sulphur  in  the  sulphides  of  the  metals  of 
the  alkalies  and  alkaline  earths  soluble  in  water  is  best  effected — pro- 
vided they  are  free  from  excess  of  sulphur — by  I.,  b or  c.  The  bases  are 
conveniently  estimated  in  a separate  portion,  which  is  decomposed  by 
evaporation  with  hydrochloric  or  sulphuric  acid,  or — when  none  but 
alkali-metals  are  present — by  ignition  with  5 parts  of  chloride  of  ammo- 
nium in  a porcelain  crucible.  If  the  said  compounds  contain  excess 
of  sulphur  they  should  be  oxidized  either  by  chlorine  in  alkaline  solu- 
tion, or  treated  according  to  J5,  c,  or  C y if  they  contain  hyposulphite  or 
sulphite,  proceed  according  to  § 168. 


* Compt.  Rend.  37,  835  ; Journ.  f.  prakt.  Chem.  61,  134. 


328 


DETERMINATION-. 


[§  149. 


b.  Tlie  sulphur  contained  in  alkaline  fluids  as  monosulphide  or  hydro- 
sulphate of  the  sulphide  may  also  he  determined  directly  by  volumetric 
analysis,  by  means  of  a standard  ammoniacal  zinc  or  silver  solution.  The 
former  is  added  to  the  solution  of  the  sulphide  of  the  alkali-metal  until  a 
drop  coming  in  contact  with  a drop, of  alkaline  solution  of  lead  * on  fil- 
ter paper,  no  longer  produces  a black  line  (Fr.  MoHRf).  Or  the  latter 
reagent  is  added  to  the  fluid — previously  mixed  with  ammonia  and 
warmed — till  a further  addition  of  silver  solution  to  a filtered  portion 
only  gives  a trifling  turbidity  (Lestelle).  The  methods  are  especially 
adapted  to  technical  purposes,  e.  g.,  for  the  estimation  of  the  sulphide  of 
sodium  in  soda-lyes,  &c. 


third  group. 

NITRIC  ACID. — CHLORIC  ACID. 

§ 149. 

1.  Nitric  Acid. 

I.  Determination. 

Free  nitric  acid  in  a solution  containing  no  other  acid  is  determined 
most  simply  in  the  volumetric  way,  by  neutralizing  with  a dilute  solu- 
tion of  soda  of  known  strength  (comp.  Special  Part,  “ Acidimetry  ”). 
The  following  method  also  effects  the  same  purpose : Mix  the  solution 
with  baryta  water,  until  the  reaction  is  just  alkaline,  evaporate  slowly  in 
the  air,  nearly  to  dryness,  dilute  the  residue  with  water,  filter  the  solu- 
tion which  has  ceased  to  be  alkaline,  wash  the  carbonate  of  baryta  formed 
by  the  action  of  the  carbonic  acid  of  the  atmosphere  upon  the  excess  of 
the  baryta  water,  add  the  washings  to  the  filtrate,  and  determine  in  the 
fluid  the  baryta  as  directed  in  § 101.  Calculate  for  each  1 eq.  baryta  1 
eq.  nitric  acid.  Lastly,  free  nitric  acid  ma}^  also  be  determined  in  a sim- 
ple manner  by  supersaturating  with  ammonia,  evaporating  in  a.  weighed 
platinum  dish,  drying  the  residue  at  110°  to  120°,  and  weighing  the 
NH4  O,  N 05  (Schaffgotsch). 

II.  Separation  of  nitric  acid  from  tlie  bases , and  determination  of 
the  acid  in  nitrates. 

The  determination  of  nitric  acid  in  nitrates  is  an  important  and  occa- 
sionally a difficult  problem,  which  has  of  late  years  much  occupied  the 
attention  of  chemists.  Before  entering  upon  the  consideration  of  the 
question,  I would  lay  it  down  as  a general  rule,  that  whatever  method 
may  be  selected,  it  should  always  first  be  tried  repeatedly  upon  weighed 
quantities  of  a pure  nitrate,  that  some  familiarity  with  the  details  of 
these  rather  complicated  processes  may  be  acquired.  Considering  the 
great  number  of  methods  that  have  been  proposed,  I shall  confine  myself 
to  describing  the  simplest  and  the  best. 

a Methods  based  on  the  expulsion  of  the  Acid,  in  the  Dry  Way. 

a.  In  salts  of  the  heavy  metals  or  the  earths,  the  determination  of 
nitric  acid  maybe  effected  by  simple  ignition  of  the  anhydrous  compound. 


* Made  by  mixing  sugar  of  le^d,  Rochelle  salt,  and  solution  of  soda, 
f Lehrbuch  der  Titrirmethode,  2te  Aufl.  379. 


NITRIC  ACID. 


329 


§ 149.] 


If  we  are  certain  that  the  oxides  remain  in  the  same  condition  in  which 
they  were  contained  in  the  decomposed  salt,  the  loss  of  weight  indicates 
at  once  the  quantity  of  nitric  acid  present. 

j3.  In  the  case  of  nitrates,  whose  residue  on  ignition  has  no  constant 
composition,  or  by  whose  ignition  the  crucible  is  much  attacked  (alkaline 
and  alkaline  earthy  nitrates),  fuse  the  substance  (which  must  be  anhy- 
drous and  also  free  from  organic  and  other  volatile  bodies)  with  a non-vola- 
tile flux,  and  estimate  the  nitric  acid  from  the  loss.  Silicic  acid  is  the  best 
flux,  as  it  may  be  readily  procured,  and  the  execution  is  the  most  easy 
and  the  most  certain  to  succeed.  I shall  describe  the  method  in  its 
application  to  nitrate  of  potassa  or  soda. 

F use  the  latter  at  a low  temperature,  pour  out  on  to  a warm  porcelain 
dish,  powder  and  dry  again  before  weighing.  Now  transfer  to  a plati- 
num crucible  2 to  3 grm.  powdered  quartz,  ignite  well  and  weigh  after 
cooling.  Add  about  0‘5  grm.  of  the  salt  prepared  as  above,  mix  well, 
and  convince  yourself  by  the  balance  that  nothing  has  been  lost  during 
mixing.  The  covered  crucible  is  then  exposed  to  a low  red  heat  (just 
visible  by  day)  for  half  an  hour,  and  weighed  after  cooling  with  the 
cover.  The  loss  of  weight  represents  the  quantity  of  nitric  acid.  Sul- 
phates or  chlorides  are  not  decomposed  at  the  given  temperature ; if  a 
higher  heat  be  applied,  the  latter  may  volatilize.  The  action  of  reducing 
gases  must  be  avoided.  The  test-analyses,  communicated  by  Reich,*  as  well 
as  those  performed  in  my  own  laboratory,!  gave  very  satisfactory  results. 

b.  Method  based  on  the  distillation  of  the  Hydrate  of  Nitric  Acid. 

All  nitrates  may  be  decomposed  by  distillation  with  moderately  dilute 
sulphuric  acid.  The  nitric  acid  passing  into  the  receiver  may  then  be  de- 
termined, according  to  I.,  volumetrically  or  gravimetrically.  1 to  2 grm. 
of  the  nitrate  should  be  treated  with  a cooled  mixture  of  1 volume  con- 
centrated sulphuric  acid  and  2 volumes  water.  For  1 grm.  nitre  take  5 
c.  c.  sulphuric  acid  and  10  c.  c.  water.  The  distillation  may  be  performed 
either  with  a thermometer  at  160°  to  170°  in  a paraffin  or  sand-bath 
(duration  of  the  distillation  for  1 to  2 grm.  nitre,  3 to  4 hours),  or  in 
vacuo , with  the  use  of  a water-bath.  The  latter  process  is  the  best.  In 
the  former,  the  neck  of  the  tubulated  retort  (which  is  drawn  out  and 
bent  down)  is  connected  with  a bulbed  U-tube|  containing  a measured 
quantity  of  normal  soda  or  potassa  solution  (§  ).  The  distillation  in 

vacuo  may  be  conducted,  without  the  use  of  an  air  pump,  according  to 
FinkenerJ  as  follows:  transfer  the  measured  quantity  of  water  and 
concentrated  sulphuric  acid  to  the  tubulated  retort,  and  the  necessary 
quantity  of  standard  potassa  or  soda  solution  diluted  to  30  c.  c.,  to  a flask 
with  a narrow  neck  of  about  200  c.  c.  capacity.  Then,  by  means  of  an  india- 
rubber  tube,  connect  the  flask  with  the  retort  air-tight,  so  that  the  drawn- 
out  point  of  the  latter  may  extend  to  the  body  of  the  flask,  and — with 
tubulure  open — heat  the  contents  of  the  retort  and  of  the  flask  to  boiling. 
When  the  air  has  been  expelled  from  the  apparatus  by  long  boiling,  trans- 
fer the  salt  (weighed  in  a small  tube)  to  the  retort  through  the  tubulure, 
close  the  latter  immediately,  and  at  the  same  time  take  away  the  lamp. 
The  retort  is  then  heated  with  a water-bath,  the  flask  being  kept  cool. 

* Berg-  und  Hiittenmannische  Zeitschrift,  1861,  No.  21 ; Zeitschrift  f.  analyt. 
Chem.  1,  86. 

+ Zeitschrift  f.  analyt.  Chem.  1.  181. 

! The  bulbed  U-tube  will  be  found  figured  § 185. 

|j  Zeitschrift  f . analyt.  Chem.  1 , 309. 


330 


DETERMINATION. 


[§  U9. 


The  quantity  of  nitric  acid  that  has  passed  over  is  finally  ascertained  by 
determining  the  still  free  alkali  with  standard  acid.  If  it  is  suspected 
that  all  the  nitric  acid  has  not  been  driven  into  the  receiver  by  one  distil- 
lation, you  may — by  heating  the  flask  and  cooling  the  retort — distil  the 
water  back  into  the  latter,  and  then  the  distillation  from  the  retort  may 
be  repeated.  The  distillate  thus  obtained  is  always  free  from  sulphuric 
acid,  hence  the  results  are  very  exact.  The  base  remains  as  sulphate  in 
the  retort.  In  the  presence  of  chloride  add  to  the  contents  of  the  retort 
a sufficiency  of  dissolved  sulphate  of  silver,  or — when  much  chloride  is 
present — moist  oxide  of  silver.  The  nitric  acid  is  then  obtained  entirely 
free  from  chlorine. 

c.  Methods  based  on  the  decomposition  of  Nitrates  by  Alkalies , cfic. 

a.  Nitrates,  whose  bases  are  completely  separated  by  caustic  or  car- 
bonated alkalies — provided  basic  salts  are  not  precipitated  at  the  same 
time — may  be  analyzed  by  simple  boiling  with  an  excess  of  standard 
potassa  or  soda  or  their  carbonates.  After  cooling,  dilute  to  \ or  ^ litre, 
mix,  allow  to  settle,  draw  off  a portion  of  the  supernatant  clear  fluid,  de- 
termine the  free  alkali  remaining  in  it,  and  calculate  therefrom  the  amount 
consumed  by  the  nitric  acid.  Hayes  obtained  with  the  nitrates  of  silver 
and  bismuth  good  results ; but  with  subnitrate  of  mercury  (using  carbon- 
ate of  soda)  the  results  were  not  so  satisfactory.* 

0.  In  nitrates,  whose  bases  are  precipitated  by  hydrate  of  baryta  or 
lime,  or  by  their  carbonates  (or  by  sulphide  of  barium),  the  nitric  acid 
may  be  estimated  with  great  accuracy  by  filtering,  after  precipitation  has 
been  effected,  warm  or  cold,  passing  carbonic  acid  through  the  filtrate,  if 
necessary,  till  all  the  baryta  is  precipitated,  warming,  filtering,  and  deter- 
mining the  baryta  in  the  filtrate  by  sulphuric  acid.  1 eq.  of  the  same  cor- 
responds to  1 eq.  of  nitric  acid.  [In  case  of  bismuth-salts,  boil  until  the 
separated  oxide  is  perfectly  yellow.  Paige]. 

y.  In  many  nitrates  whose  bases  are  precipitable  by  sulphuretted  hy- 
drogen the  nitric  acid  may  be  determined  according  to  Gibbs  by  adding 
to  the  salt  in  solution  about  its  own  weight  of  some  neutral  organic  salt, 
e.g .,  Rochelle  salt,  and  throwing  down  the  metal  by  HS.  The  filtrate  and 
washings  are  brought  to  a definite  bulk  and  the  free  acid  is  determined  in 
aliquot  portions  alkalimetrically.f 

d.  Methods  based  upon  the  decomposition  of  the  Nitric  Acid  by  Proto- 
chloride of  Iron. 

Method  of  PelouzeJ;  and  Fresenius.  The  decomposition  is  as  fol- 
lows : 

6 Fe  Cl-j-K  O,  N 05-f  4 H Cl  = 4 H O + K Cl +3  Fe  Cl3+N  02. 

a.  Select  a tubulated  retort  of  about  200  c.  c.  capacity,  with  a long  neckf 
and  fix  it  so  that  the  latter  is  inclined  a little  upwards.  Introduce  into 
the  body  of  the  retort  about  1*5  grm.  fine  pianoforte  wire,  accurately 
weighed,  and  add  about  30  or  40  c.  c.  pure  fuming  hydrochloric  acid. 
Conduct  now  through  the  tubulure,  by  means  of  a glass  tube  reaching 
only  about  2 cm.  into  the  retort,  hydrogen  gas  washed  by  solution  of 
potassa,  or  pure  carbonic  acid,  and  connect  the  neck  of  the  retort  with  a 
TJ-tube  containing  some  water.  Place  the  body  of  the  retort  on  a water- 
bath,  and  heat  gently  until  the  iron  is  dissolved.  Let  the  contents  of 


* H.  Rose,  Zeitschrift  f.  analyt.  Chem.  1,  306. 
+ Am.  Jour.  Sci.  xliv.,  209. 

| Joum.  f.  prakt.  Chem.  40,  324. 


§ 149.] 


NITRIC  ACID. 


331 


the  retort  cool  in  the  current  of  hydrogen  gas  or  carbonic  acid  ; increase 
the  latter,  and  drop  in,  through  the  neck  of  the  retort,  into  the  body,  a 
small  tube  containing  a weighed  portion  of  the  nitrate  under  examina- 
tion, which  should  not  contain  more  than  about  0*200  grm.  of  nitric 
acid.  After  restoring  the  connection  between  the  neck  and  the  U-tube, 
heat  the  contents  of  the  retort  in  the  water-bath  for  about  a quarter  of 
an  hour,  then  remove  the  water-bath,  heat  with  the  lamp  to  boiling,  un- 
til the  fluid,  to  which  the  nitric  oxide  had  imparted  a dark  tint,  shows 
the  color  of  sesquichloride  of  iron,  and  continue  boiling  for  some  minutes 
longer.  Care  must  be  taken  to  give  the  fluid  an  occasional  shake,  to 
prevent  the  deposition  of  dry  salt  on  the  sides  of  the  retort.  Before  you 
discontinue  boiling,  increase  the  current  of  hydrogen  or  carbonic  acid 
gas,  that  no  air  may  enter  through  the  U-tube  when  the  lamp  is  removed. 
Let  the  contents  cool  in  the  current  of  gas,  dilute  copiously  with  water, 
and  determine  the  iron  still  present  as  protocliloride  by  permanganate 
(see  Note,  p.  198) — 168  of  iron  converted  by  the  nitric  acid  from  the  state 
of  proto-  to  that  of  sesquichloride  correspond  to  54  of  nitric  acid.  My 
test-analyses  of  pure  nitrate  of  potassa  gave  100*1 — 100*03 — 100*03,  and 
100*05  instead  of  100.*  [The  remaining  sesquioxide  may  also  be  deter- 
mined by  hyposulphite  of  soda,  p.  203,  3 6.]. 

[/?.  Schlosing’s  method,  f modified  by  Fruhling  and  Grouven.J 

The  following  method,  employed  by  Schlosing,  more  particularly  to 
determine  nitric  acid  in  tobacco,  and  which  affords  this  very  important 
advantage,  that  it  may  be  used  in  presence  of  organic  matter,  has  suc- 
cessfully passed  through  the  ordeal  of  numerous  and  searching  experi- 
ments. 

The  dissolved  nitrate  is  intro- 
duced into  a flask  of  400  c.  c. 
capacity,  fig.  62,  which  is  con- 
nected, by  means  of  an  india- 
rubber  stopper,  with  a narrow 
glass  tube,  a , which  is  joined  by 
means  of  a rubber  tube  8 cm. 
long,  with  another  glass  tube 
that  is  again  terminated  at  d , 
by  a piece  of  rubber  tube.  At 
c a pinch-cock  is  placed.  The 
solution  of  the  nitrate,  which 
must  be  neutral  or  alkaline,  is 
heated  to  boiling,  d being  sta- 
tioned in  a beaker  of  water, 
until  the  atmospheric  air  is 
perfectly  expelled  from  the  apparatus.  When  the  vapors  that  pass  over 
completely  condense  in  d , the  pinch-cock  c is  closed  and  the  lamp  is 
removed.  Water  immediately  rises  in  the  tube  and  fills  it  entirely  to 
c.  Shortly  the  vapors  in  the  flask  condense,  as  shown  by  the  collapse  of 
the  rubber  tube  at  c.  At  this  moment  the  tube  d is  removed  from  the 
water  and  dipped  in  a glass  containing  a solution  of  protochloride  of 
iron  in  hydrochloric  acid. 


* Annal.  d.  Chem.  u.  Pharm.  106,  217. 

+ Annal.  de  Chim.  3 ser.  tom.  40,  479  ; Joum.  f.  prakt.  Chem.  62,  142. 
\ Versuchs-Stationen,  IX.  14. 


332 


DETERMINATION. 


The  pinch-cock  is  cautiously  opened  so  as  to  allow  the  protochloride 
to  enter  the  flask  slowly.  When  sufficient  of  the  iron  solution  has  been 
introduced,  the  pinch-cock  is  closed,  and  d is  brought  into  a vessel  of 
hydrochloric  acid,  and  portions  of  this  are  made  to  enter  the  flask  in  the 
same  manner  repeatedly  until  the  tubes  are  completely  washed  of  all  pro- 
tochloride. In  these  operations,  as  in  all  the  subsequent  transfers,  it  is  need- 
ful to  exclude  all  traces  of  air,  which  is  easy,  provided  the  drop  of  liquid 
that  hangs  to  d when  it  is  carried  from  one  liquid  to  another,  is  not  allowed 
to  fall  off.  Finally,  the  tube  is  rinsed  once  by  allowing  boiling  water 
to  recede,  and  then,  the  cock  being  closed,  the  tube  d , still  full  of  water, 
is  passed  into  the  lateral  tubulure  of  the  receiver,  fig.  63,  which  stands 
immersed  in  mercury. 

The  flask  is  again  gently  heated  and  its  contents  immediately  boil 
with  violent  thumping.  The  solution  becomes  black,  and  shortly  the 
collapsed1  rubber  tube  at  c shows  that  there  is  interior  pressure.  As 
soon  as  this  is  evident,  open  the  cock  and  allow  the  nitric  oxide  gas  to 
pass  over  into  the  receiver. 

The  receiver,  fig.  63,  has  a rough-ground  neck,  which  is  connected  by 
rubber,/*,  with  a brass  cock ; * the  latter  is  likewise  joined  by  rubber  to 
a short  glass  tube,  g.  Into  this  receiver,  the  cock 
being  open,  some  water,  freed  from  air  by  long  boil- 
ing and  cooled  in  a closed  vessel,  is  introduced  by  a 
tall  funnel-tube  fitted  into  the  tubulure,  and  then 
mercury  is  poured  in  until  it  fills  the  vessel  up  to 
the  lower  edge  of  the  rubber,  f.  In  this  operation 
the  cock  and  small  tube,  g , should  be  overfilled  with 
the  water  previously  added.  The  receiver  is  thus 
empty  of  all  air,  and  stands  with  the  tubulure  cov- 
ered with  mercury,  as  in  fig.  64. 

By  means  of  a pipette,  having  a narrow  rubber 
tube  slipped  over  its  tip,  about  50  c.  c.  of  thick  and 
well-boiled  milk  of  lime  are  passed  into  the  receiver 
through  the  tubulure.  This  is  to  absorb  the  hydro- 
chloric acid  which  boils  over  from  the  flask,  and  the 
receiver  is  shaken  to  facilitate  the  absorption. 

The  nitric  oxide,  expelled  from  the  flask  by  continual  boiling,  gathers  in 
the  receiver  in  a state  of  purity.  The  period  of  its  complete  transfer  is  ex- 
actly marked  by  the  deposition  of  the  milk  of  lime,  which  is  thrown  into 
agitation  by  the  passage  of  a permanent  gas,  but  quietly  condenses  or 
absorbs  steam  and  hydrochloric  acid.  The  completion  of  the  reaction  is 
also  indicated,  in  case  pure  nitrates  are  employed,  by  the  liquid  in  the 
flask  assuming  the  color  of  pure  sesquichloride  of  iron.  When  dark 
vegetable  extracts  are  under  analysis  this  indication  is  not  offered. 

Should  the  nitric  oxide  come  off  in  quantity  greater  than  the  receiver 
can  contain  at  once,  the  cocks  are  closed  and  the  lamp  is  removed  from 
under  the  fkisk. 

The  receiver  is  then  emptied,  as  is  subsequently  described,  charged 
anew  with  water,  mercury,  and  milk  of  lime,  reconnected,  and  the  boil- 
ing resumed. 

When  the  nitric  oxide  has  been  completely  collected  in  the  receiver, 


[*  Such  receivers  (Bunsen’s  gasometer)  may  be  procured  with  a glass  stop- 
cock.] 


NITRIC  ACID. 


333 


§ 149.] 

it  must  be  transferred  to  a second  flask,  to  be  converted  into  nitric 
acid. 

This  flask,  fig.  64,  arranged  like  the  one  already  described,  contains  at 
first  about  100  c.  c.  of  pure  water,  which  is  boiled  to  expel  all  atmo- 
spheric air,  and  while  still  boiling  vigorously  is  connected  with  the 
receiver  by  passing  the  end  of  the  tube  x over  the  glass  tube  g , of  the 
latter.  The  lamp  is  then  removed,  and  when  collapse  of  the  rubber  tube 
takes  place,  the  brass  stopcock  of  the  receiver  is  slightly  and  cautiously 
opened  and  the  gas  allowed  to  recede  into  the  flask  until  the  milk  of 
lime  reaches  the  lower  edge  of  f.  The  cock  is  then  closed  and  the  last 
portions  of  nitric  oxide  are  rinsed  into  the  flask  by  passing  into  the 
receiver  a few  (20-30)  c.  c.  of  pure  hydrogen  (washed  by  passing  through 
oil  of  vitriol  and  milk  of  lime),  and  allowing  this  to  recede  in  the  same 
way.  This  rinsing  is  repeated  three  or  four  times.  The  rubber  tube 
is  now  closed  by  a pinch-cock  at  y,  and  disconnected  from  the  receiver. 
It  is  then  united  in  the  same  manner  with  a gas-holder  containing  pure 
oxygen  under  pressure,  and  the  gas  is  made  to  enter  the  flask.  It  is 
absorbed  with  the  appearance  of  red  fumes  and  the  formation  of  nitric 
acid.  After  half  an  hour  or  so,  the  flask  being  occasionally  shaken,  the 
nitric  acid  is  dissolved  in  the  water  of  the  flask,  and  may  be  estimated 
by  a standard  alkaline  solution,  § — . 


Fruhling  and  Grouven,  who  applied  this  method  to  the  estimation 
of  nitrates  in  plants,  extracted  the  dried  vegetable  with  alcohol  of  50 
per  cent.,  evaporated  the  solution  to  a small  volume,  precipitated  with 
caustic  lime,  and  employed  the  filtrate  for  the  analysis.  For  details, 
see  their  paper,  loc.  cit .] 

[e.  Method  based  on  the  conversion  of  the  Nitric  Acid  into  Ammonia. 

If  a nitrate  be  placed  cold  in  an  acid,  or  be  heated  in  an  alkaline  fluid 
in  which  nascent  hydrogen  is  evolved  in  sufficient  quantity,  all  the  nitric 
acid  may  be  converted  into  ammonia,  so  that  from  the  amount  of  the 
latter  the  quantity  of  the  nitric  acid  may  be  accurately  deduced,  ISTesbit* 
was  the  first  to  arrange  a method  for  the  determination  of  our  acid  on  this 


Quart.  Joum  Chem.  Soc.  1,  p.  281. 


334  DETERMINATION.  [§  149. 

principle.  Afterwards  Schulze,*  Harcourt,!  and  SiewertJ  suggested 
processes  with  the  same  object.  Nesbit  reduces  with  zinc  in  acid  solu- 
tion. The  others  reduce  in  alkaline  solution,  Schulze  with  platinized 
zinc,  Harcourt  and  Siewert  with  zinc  and  iron  filings. 

To  reduce  0*65  grm.  (10  grains,  of  nitre,  Nesbit  directs  to  place  15  or 
20  grm.  of  thin  clean  fragments  of  zinc  in  a flask  with  some  water. 
From  15  to  20  c.c.  of  hydrochloric  acid,  sp.  gr.  T17,  are  poured  out  into 
a small  measure,  and  about  one-tenth  part  is  added  to  the  zinc  and  water. 
When  effervescence  has  fairly  commenced,  a portion  of  the  nitrate,  pre- 
viously dissolved  in  water,  is  added  to  the  mixture.  The  temperature 
must  be  kept  low,  if  necessary,  by  placing  the  vessel  in  cold  water.  Af- 
ter a short  period  a little  more  acid  is  added,  and  then  a little  nitrate,  until 
all  the  solution  of  the  nitrate  and  the  washings  are  poured  in  and  about  one- 
fourth  of  the  acid  is  left.  Care  should  be  taken  that  for  the  first  hour  the 
effervescence  be  slow.  When  the  whole  of  the  solution  of  the  nitrate  is 
poured  in,  the  remainder  of  the  acid  must  be  added  from  time  to  time,  and 
the  whole  left  until  effervescence  ceases.  The  liquid  is  separated  from  the 
undissolved  zinc  which  is  washed  with  the  smallest  quantity  of  water,  and 
the  liquid  is  distilled  with  hydrate  of  lime,  or  potash,  and  the  ammonia 
estimated  as  directed  § 99,  3.  Instead  of  distilling  off  the  ammonia,  the 
acid  solution  is  brought  to  a volume  of,  say  50  c.c.,  and  10  c.  c.  are  treated 
in  the  azotometer  according  to  § 99,  4.  The  results  are  good  if  the 
directions  are  followed  strictly.  It  is  especially  needful  not  to  allow  the 
reducing  action  to  proceed  too  vigorously,  as  otherwise  the  mixture  gets 
warm  and  binoxide  of  nitrogen  escapes.  A similar  process  of  reduction 
has  given  good  results  in  the  hands  of  Krocker  and  Dietrich.  |] 

Siewert  employs  to  about  1 grm.  nitre,  4 grm.  iron  filings  and  8 — 10 
grm.  zinc-filings,  and  also  16  grm.  solid  hydrate  of  potassa  and  100  c.  c. 
alcohol,  0’825  sp.  gr.  By  the  use  of  alcohol  the  danger  of  the  boiling 
fluid  receding  is  got  rid  of.  His  apparatus  consists  of  a flask  of  300 — 350 
c.  c.  capacity  with  evolution  tube,  which  leads  to  the  flasks  represented  in 
fig.  65.  The  capacity  of  each  is  150 — 200  c.  c. ; they  contain  normal  acid. 

The  connecting-tube  b is  ground  obliquely 
at  both  ends,  c serves  during  the  operation 
to  hold  a strip  of  litmus  paper,  and  after 
it  to  enable  the  analyst  to  transfer  the  fluid 
from  one  flask  to  the  other  at  will.  After 
the  apparatus  has  been  put  together,  the 
disengagement  of  gas  may  be  allowed  to 
go  on  in  the  cold,  or  it  may  be  assisted 
from  the  first  by  a small  flame.  After  the 
lapse  of  half-an-hour  the  ammonia  formed 
begins  to  pass  over  in  proportion  as  the 
alcohol  distils  off.  As  soon  as  the  latter 
is  fully  removed  from  the  evolution  flask, 
heat  is  applied  with  great  caution — to 
drive  out  the  last  traces  of  ammonia — till 
steam  appears  in  the  evolution  tube,  or  10 — 15  c.  c.  alcohol  are  rapidly 
introduced  once  or  twice  into  the  evolution  flask  and  distilled  off.  Tho 
ammonia  is  determined  as  above.  Test-analyses  good. 


h c 


Fig.  65. 


* Chem.  Centralblatt,  1861,  657  u.  833.  f Joum.  of  the  Chem.  Soc.  xv.  385. 
% Anna!,  d.  Chem.  Pharm.  125,  293.  j Fres.  Zeit.  iff,  69. 


CHLORIC  ACID. 


335 


§ 150.] 


f.  Methods  in  which  the  Nitrogen  of  the  Nitric  Acid  is  separated 
and  measured  in  the  gaseous  form. 

These  methods  are  more  particularly  suitable  for  analyzing  nitrates 
which  are  decomposed  by  ignition  into  oxide  or  metal  and  oxides  of 
nitrogen ; they  will  be  found  in  the  Section  on  the  Ultimate  Analysis  of 
Organic  Bodies,  § 184.  Marignac  employed  them  to  analyze  compounds 
of  nitric  acid  with  suboxide  of  mercury.  B ROME  is  analyzed  nitrite,  &c., 
of  lead  by  a similar  method,  recommended  by  Bunsen.  In  cases  where 
it  is  intended  to  determine  the  water  of  the  analyzed  nitrate  in  the  direct 
way,  such  methods  are  almost  indispensable.* 


§ 150. 

2.  Chloric  Acid. 

I.  Determination. 

Free  chloric  acid  in  aqueous  solution  may  be  determined  by  converting 
it  into  hydrochloric  acid  by  the  agency  of  nascent  hydrogen  (II.,  c), 
and  determining  the  acid  formed,  as  directed  in  § 141 ; or  by  saturating 
with  solution  of  soda,  evaporating  the  fluid,  and  treating  the  residue  as 
directed  in  II.,  a or  b. 


II.  Separation  of  Chloric  Acid  from  the  Bases  and  Determina- 
tion of  the  Acid  in  Chlorates. 


a.  After  Bunsen.|  When  warm  hydrochloric  acid  acts  upon  chlo- 
rates, the  latter  are  reduced ; as  this  reduction  is  not  attended  with 
separation  of  oxygen,  the  following  decompositions  may  take  place  : — 


C10ft 

HC1 


CIO 
C103 
H O 


C105  ( 3 CIO 
2HC1 1 2 HO 


CIO* 

3 HC1 


(2  CIO 
■I  2 Cl 
(3  HO 


C105 
4 HC1 


( CIO 
1 4 Cl 
(4  HO 


CIO* 

5 HC1 


Uci 

1 5 HO 


Which  of  these  products  of  decomposition  may  actually  be  formed, 
whether  all  or  only  certain  of  them,  cannot  be  foreseen.  But  no  matter 
which  of  them  may  be  formed,  they  all  of  them  agree  in  this,  that,  in 
contact  with  solution  of  iodide  of  potassium,  they  liberate  for  every  1 
eq.  chloric  acid  in  the  chlorate,  6 eq.  iodine.  762  of  iodine  liberated 
correspond  accordingly  to  75’46  of  chloric  acid.  The  analytical  process 
is  conducted  as  described  § 142,  1. 

b.  After  Sestini.J  To  the  concentrated  aqueous  solution  of  the 
weighed  chlorate  add  a piece  of  zinc  and  then  some  pure  dilute  sulphuric 
acid  and  allow  to  stand  for  some  time  (with  0’1  grm.  chlorate  of  potassa, 
half  an  hour  is  sufficient).  By  the  nascent  hydrogen  the  chloric  acid  is 
converted  into  hydrochloric  acid,  which,  after  removal  and  rinsing  of  the 
zinc,  is  determined  according  to  § 141.  To  use  the  volumetric  method 
(§  141,  6,  a),  the  sulphuric  acid  is  first  precipitated  with  nitrate  of  baryta, 
then  the  zinc  and  excess  of  baryta  with  carbonate  of  soda,  the  liquid  is 
filtered  and  neutralized,  then  chromate  of  potassa  is  added,  and  finally 
standard  silver  solution. 


* See  also  Gibbs,  Am.  Joum.  Sci. , xxxvii.  350, 
f Anna!  d.  Chem.  u.  Pharm.  86,  282. 

\ Zeitschrift  f.  analyt.  Chem.  1,  500. 


336 


DETERMINATION. 


[§  15°* 


c.  The  bases  are  determined  with  advantage  in  a separate  portion, 
by  converting  the  chlorate  either  by  very  cautious  ignition,  or  by  warm- 
ing with  hydrochloric  acid  into  chloride. 

The  estimation  of  hypochlorous  acid  will  be  described  in  the  Special 
Part,  article  “ Chlorimetry.” 


SECTION  y. 


SEPARATION  OF  BODIES. 

§ 151. 

In  the  previous  Section  we  have  considered  the  methods  employed  for 
the  determination  of  bases  and  acids,  when  only  one  base  or  one  acid 
is  present.  In  the  present  Section  we  shall  treat  of  the  separation  of 
bodies,  i.  e.,  the  determination  of  the  bases  and  acids,  when  several  bases 
or  acids  are  present. 

The  separation  of  bodies  may  be  effected  in  three  ways,  viz.,  a,  by 
direct  analysis  ‘ b,  by  indirect  analysis  ’ c,  by  estimation  by  difference. 

By  direct  analysis , we  understand  the  actual  separation  of  the  bases 
or  acids.  Thus,  we  separate  potash  from  soda  by  bichloride  of  platinum ; 
copper  from  tin  by  nitric  acid ; arsenic  from  iron  by  sulphuretted  hydro- 
gen ; iodine  from  chlorine  by  nitrate  of  protoxide  of  palladium  ; phos- 
phoric acid  from  sulphuric  acid  by  baryta  ; carbon  from  nitrate  of  potassa 
by  water,  &c.,  &c.  In  direct  analysis  we  render  the  body  to  be  esti- 
mated insoluble,  while  the  other  remains  in  solution,  or  vice  versd , or  we 
volatilize  it,  leaving  the  others  behind,  or  we  effect  actual  separation  in 
some  other  manner.  This  is  the  mode  of  analysis  most  frequently  em- 
ployed. It  generally  deserves  the  preference  where  choice  is  permitted. 

We  term  an  analysis  indirect,  if  it  does  not  effect  the  actual  separation 
of  the  bodies  we  wish  to  determine,  but  causes  certain  changes  which 
enable  us  to  calculate  the  quantities  of  the  bases  or  acids,  present.  Thus 
the  quantity  of  potash  and  soda  in  a mixture  of  the  two  may  be  deter- 
mined by  converting  them  into  sulphates,  weighing  the  latter,  and  esti- 
mating the  sulphuric  acid  (§  152,  3). 

Finally,  if  we  weigh  two  bodies  together,  determine  one  of  them,  and 
subtract  its  weight  from  that  of  the  two,  , we  shall  find  the  weight  of  the 
other  body.  In  this  case  the  second  body  is  said  to  be  estimated  by 
difference.  Thus,  alumina  may  be  determined  when  mixed  with  sesqui- 
oxide  of  iron,  by  weighing  the  mixture  and  estimating  the  iron  volu- 
metrically. 

Indirect  analysis  and  estimation  by  difference  may  be  employed  in  an 
exceedingly  large  number  of  cases ; but  their  use  is  as  a r\de  only  to  be 
recommended,  where  good  methods  of  true  separation,  are  wanting.  The 
special  cases  in  which  they  are  preferable  to  direct  analysis  cannot  be  all 
foreseen  ; those  alone  are  pointed  out  which  are  of  more  frequent  occur- 
rence. As  regards  the  calculations  required  in  indirect  analysis  I have 
given  general  directions  under  the  “ Calculation  of  Analysis  ; ” where- 
ever  it  appeared  judicious,  I have  added  the  necessary  directions  to  the 
description  of  the  method  itself. 

I have  retained  our  former  subdivision  into  groups,  and,  as  far  as 
practicable,  systematically  arranged,  first,  the  general  separation  of  all 

22 


338 


SEPARATION  OF  BODIES. 


L§  151. 


the  bodies  belonging  to  one  group  from  those  of  the  preceding  groups; 
secondly,  the  separation  of  the  individual  bodies  of  one  group  from  all  or 
from  certain  bodies  of  the  preceding  groups ; and  finally,  the  separation 
of  bodies  belonging  to  one  and  the  same  group  from  each  other.  I think 
I need  scarcely  observe  that  the  general  methods  which  serve  to  separate 
the  whole  of  the  bodies  of  one  group  from  those  of  another  group,  are 
also  applicable  to  the  separation  of  every  individual  body  of  the  one 
group  from  one  or  several  bodies  of  the  other  group.  It  must  not  be 
understood  that  the  more  special  methods  are  necessarily  in  all  cases 
preferable  to  the  more  general  ones.  As  a rule  it  must  be  left  to  indi- 
vidual chemists  to  decide  for  themselves  in  each  special  case  which 
method  should  be  adopted.  With  respect  to  the  general  methods  for  se- 
parating one  group  from  another,  I would  observe  that  those  adduced 
appeared  to  me  more  adapted  to  the  purpose  than  others,  but  still  there 
may  be  other  that  are  equally  suitable,  and  in  special  cases  even  more  so. 
A wide  field  is  here  open  to  the  ingenuity  of  the  analyst. 

The  methods  given  for  the  separation  of  both  bases  and  acids  are 
generally  based  upon  the  supposition  that  they  are  in  the  free  state,  and 
in  the  form  of  salts  soluble  in  water.  Wherever  this  is  not  the  case, 
special  mention  is  made  of  the  circumstance. 

From  among  the  host  of  proposed  methods,  I have,  as  far  as  practica- 
ble, chosen  those  which  have  been  sanctioned  by  experience  and  are  dis- 
tinguished for  accurate  results.  In  cases  where  two  methods  were  on  a 
par  with  each  other  as  regards  these  two  points,  I have  either  given  both, 
or  selected  the  more  simple  one.  Methods  which  experience  has  shown  to 
be  defective  or  fallacious  have  been  altogether  omitted.  I have  endeavored 
to  point  out,  as  far  as  possible,  the  particular  circumstances  under  which 
either  the  one  or  the  other  of  several  methods  deserve  the  preference. 

Where  the  accuracy  of  an  analytical  method  has  been  established 
already,  in  Section  IV.,  no  further  statements  are  made  on  the  subject 
here.  Paragraphs  of  former  Sections  deserving  particular  attention  are 
referred  to  in  parentheses. 

The  extension  of  chemical  science  introduces  almost  every  day  new 
analytical  methods  of  every  description,  which  are,  rightly  or  wrongly, 
preferred  to  the  older  methods  ; the  present  time  may  therefore  be  looked 
upon  in  this,  as  in  so  many  other  respects,  as  a period  of  transition,  in 
which  the  new  strives  more  than  ever  to  overcome  and  supplant  the  old. 
I make  this  remark  to  show  the  impossibility  of  always  adding  to  the 
description  of  a method  an  opinion  of  its  usefulness  and  accuracy,  and 
also  to  point  out  the  importance,  under  such  circumstances,  of  a proper 
systematic  arrangement.  I have  in  this  Section  generally  arranged  the 
various  analytical  methods  upon  the  basis  of  their  scientific  principles, 
firmly  persuaded  that  this  will  greatly  tend  to  facilitate  the  study  of  the 
science,  and  will  lead  to  endeavors  to  apply  known  principles  to  the  sepa- 
ration of  other  bodies  besides  those  to  which  they  are  already  applied,  or 
to  apply  new  principles  where  experience  has  proved  the  old  ones  falla- 
cious, and  the  methods  based  on  them  defective. 

I conclude  these  introductory  remarks,  with  the  important  caution  to 
the  student,  never  to  look  upon  a separation  as  successfully  accomplished , 
beforehe  has  convinced  himself  that  the  weighed  precipitates , <&c.,  are  pure, 
and  free  from  those  bodies  from  which  it  was  intended  to  separate  them. 


§ 152.] 


BASES  OF  GROUP  I. 


339 


L SEPARATION  OF  THE  BASES  FROM  EACH  OTHER. 

FIRST  GROUP. 

POTASSA SODA AMMONIA (LITHIA)  .* 

§ 152. 

Index  : — The  Nos.  refer  to  those  in  the  margin. 

Potassa  from  soda,  1 , 5. 

“ “ ammonia,  3.  4. 

Soda  from  potassa,  1,  5. 

“ *k  ammonia,  3,  4. 

Ammonia  from  potassa,  3,  4. 

“ “ soda,  3,  4. 

{Lithia  from  the  other  alkalies,  6,  7,  8.) 

1 . Methods  based  upon  the  different  Degrees  of  Solubility  in  Alcohol , 
of  the  Double  Chlorides  of  the  Alkali  Metals  and  Dichloride 
of  Platinum .) 

a.  Potassa  from  soda. 

It  is  an  indispensable  condition  in  this  method  that  the  two  alkalies  1 
should  exist  in  the  form  of  chlorides.  If,  therefore,  they  are  present  in 
any  other  form,  they  must  be  first  converted  into  chlorides,  which  in 
most  cases  may  be  effected  by  evaporation  with  hydrochloric  acid  in 
excess  ; in  the  case  of  nitrates  the  evaporation  with  hydrochloric  acid 
must  be  repeated  4 — 6 times  till  the  weight  of  the  gently  ignited  mass 
ceases  to  diminish.  In  presence  of  sulphuric  acid,  phosphoric  acid, 
and  boracic  acid,  this  simple  method  will  not  answer.  For  the  methods 
of  separating  the  alkalies  from  the  two  latter  acids,  and  converting 
them  into  chlorides,  see  §§  135  and  136.  The  presence  of  sulphuric 
acid  being  a circumstance  of  rather  frequent  occurrence,  the  way  of 
meeting  this  contingency  is  given  below  (2). 

Determine  the  total  quantity  of  the  chloride  of  sodium  and  chloride 
of  potassium  f (§§  97,  98),  dissolve  in  a small  portion  of  water,  add  an 
excess  of  a concentrated  neutral  solution  of  bichloride  of  platinum  in 
water,  evaporate  on  the  water-bath  nearly  to  dryness  (the  double 
chloride  of  platinum  and  sodium  should  not  lose  its  water  of  crystal- 
lization), treat  the  residue  with  alcohol  of  from  *86  to  ’87  sp.  gr.,  cover 
the  beaker  or  dish  with  a glass  plate,  and  allow  to  stand  a few  hours, 
with  occasional  stirring.  If  the  supernatant  fluid  appears  of  a deep 
yellow  color,  this  is  a proof  that  a sufficient  quantity  of  bichloride  of 
platinum  has  been  used  to  precipitate  the  whole  of  the  potassium. 
When  the  precipitate  has  settled,  pour  off  the  clear  fluid  through  a 
weighed  filter  and  examine  the  precipitate  most  minutely,  if  necessary, 
with  the  aid  of  a microscope.  If  it  is  a heavy  yellow  powder  (suffi- 
ciently magnified,  small  octahedral  crystals,  it  is  the  pure  chloride  of 


* With  regard  to  the  separation  of  the  oxides  of  cgesium  and  rubidium  from  the 
other  alkalies,  see  Watts’  Dictionary  of  Chemistry,  1.  p.  1113. 

f Never  weigh  the  chlorides  of  the  alkali  metals  before  you  have  convinced 
yourself  of  their  purity  by  dissolving  them  in  water,  which  should  give  a clear 
solution,  and  testing  this  solution  with  ammonia  and  carbonate  of  ammonia,  which 
must  throw  down  no  precipitate.  It  may  be  thought,  perhaps,  that  a matter  so 
simple  need  not  be  mentioned  here  ; still,  I have  found  that  neglect  in  this  respect 
is  by  no  means  uncommon. 


340 


SEPARATION. 


platinum  and  potassium.*  Then  transfer  it — best  with  the  aid  of  the 
hltrate — to  the  filter,  wash  it  with  spirit  of  *86  to  *87  sp.  gr.  and 
proceed  according  to  § 97.  If,  on  the  contrary,  white  saline  particles 
(chloride  of  sodium)  are  to  be  seen  mixed  with  the  yellow  crystalline 
powder,  bichloride  of  platinum  has  been  wanting,  the  wdiole  of  the 
chloride  of  sodium  not  having  been  completely  converted  into  chlo- 
ride of  sodium  and  platinum.  In  this  case  the  precipitate  in  the  dish 
must  be  treated  with  some  water,  till  all  the  chloride  of  sodium  is 
dissolved,  a fresh  portion  of  bichloride  of  platinum  is  added,  the 
whole  evaporated  nearly  to  dryness,  and  the  above  examination  re- 
peated. The  quantity  of  the  soda  is  usually  estimated  by  subtracting 
from  the  united  weight  of  the  chloride  of  sodium  and  chloride  of  potas- 
sium the  weight  of  the  latter,  calculated  from  that  of  the  potassio- 
bichloride  of  platinum. 

To  make  quite  sure  that  the  potassa  has  completely  separated,  it  is 
advisable  to  add  to  the  filtrate  some  water,  some  more  bichloride  of 
platinum,  and,  if  the  quantity  of  soda  is  only  small,  also  some  chloride 
of  sodium  ; evaporate  on  the  water-bath  nearly  to  dryness,  at  a tem- 
perature not  exceeding  75°  (Bisciiof),  and  treat  the  residue  in  the 
manner  just  described.  In  order  to  diminish  the  solvent  action  of  the 
spirit  on  the  chloride  of  potassium  and  platinum,  ± ether  may  be  now 
mixed  with  it.  Should  this  operation  again  leave  a small  undissolved 
residue  of  chloride  of  potassium  and  platinum,  it  is  filtered  off,  best  on 
a separate  filter,  determined  by  itself,  and  the  number  added  to  the 
principal  amount. 

I prefer  subjecting  the  filtrate  to  this  examination,  to  the  process  of 
evaporating  it  to  dryness,  igniting  the  residue  with  addition  of  some 
oxalic  acid,  or  in  a current  of  hydrogen,  extracting  with  water  and 
determining  the  chloride  of  sodium  in  the  solution  obtained  ; since, 
after  all,  the  estimation  of  the  soda  here  is  only  apparently  direct : if 
the  chloride  of  potassium  has  not  completely  separated,  the  portion 
still  remaining  in  the  filtrate  will,  of  course,  be  obtained  now  mixed 
with  ^he  chloride  of  sodium.  The  latter  method  can  therefore  only 
afford  a control  to  determine  whether  a loss  of  substance  has  been 
sustained  in  the  operation.  Instead  of  the  process  given  for  the  direct 
determination  of  soda,  the  filtrate  containing  the  double  chloride 
of  platinum  and  sodium  may  also  be  evaporated  to  dryness  with 
addition  of  sulphuric  acid,  the  residue  ignited,  the  sulphate  of  soda 
extracted  with  water  and  determined  according  to  § 98,  1 (A.  Mit- 
scheruch). 

Should  the  solution  contain  sulphuric  acid,  it  may  be  in  presence  of  2 
hydrochloric  acid  or  of  some  volatile  acid,  convert  the  alkalies  first  into 
neutral  sulphates  (§§  97,  98),  and  weigh  them  as  such.  Dissolve  in  a 
little  water,  and  add  an  alcoholic  solution  of  chloride  of  strontium, 
slightly  in  excess.  (The  quantity  of  spirit  of  wine  in  the  fluid  must 
not  be  so  large  as  to  precipitate  chloride  of  sodium  or  chloride  of  potas- 
sium.) Allow  to  deposit,  filter,  and  wash  the  sulphhate  of  strontia 
(which  if  weighed  yields  an  exact  control  of  the  analysis — compare 
§ 152,  3)  with  weak  spirit  of  wine,  until  the  washings  no  longer  leave 


* If  small  tesseral  crystals  are  visible  of  a dark  orange  yellow  color,  and  rela- 
tively large  size,  and  appearing  transparent  by  transmitted  light,  then  the  double 
, chloride  contains  chloride  of  platinum  and  lithium  (Jenzsch). 


BASES  OF  GROUP  I. 


341 


§ 152.] 


a residue  upon  evaporation  on  a watch-glass  ; evaporate  the  filtrate 
until  the  spirit  of  wine  is  completely  driven  off,  dissolve  the  residue  in 
a very  small  quantity  of  water,  add  bichloride  of  platinum,  and  proceed 
as  directed  above.  The  minute  portion  of  chloride  of  strontium  added 
in  excess  dissolves,  either  in  that  form,  or  as  strontio-bichloride  of  pla- 
tinum, together  with  the  sodio-bichloride  of  platinum,  in  spirit  of 
wine. 

Instead  of  this  method,  the  following  process  may  be  resorted  to  : — 
Dissolve  the  sulphates  of  the  alkalies  in  water,  and  add  baryta  water, 
free  from  alkali,  as  long  as  a precipitate  forms ; allow  to  deposit,  fil- 
ter, wash  the  precipitate,  and  conduct  carbonic  acid  into  the  filtrate, 
to  throw  down  the  excess  of  baryta ; heat  to  boiling,  filter  the  precipi- 
tated carbonate  of  baryta,  wash,  add  hydrochloric  acid  to  the  filtrate, 
and  evaporate  to  dryness. 

Repeated  experiments  have  shown  that  the  process  of  separating 
potassa  and  soda,  as  described  above,  gives  always  a little  less  potassa 
than  is  really  present.  If  the  process  is  properly  conducted,  the  loss 
of  potassa  amounts  to  no  more  than  1 per  cent.  I haVe  found  that  it 
is  usually  greater  in  cases  where  the  concentrated  solution  of  the  me- 
tallic chlorides  is  mixed  with  bichloride  of  platinum,  and  then  with 
a rather  large  quantity  of  alcohol.  [See  also  Finkener,  Pogg.  Ann. 
xxix.,  p.  637.] 

2.  Methods  based  upon  the  Volatility  of  Ammonia  and  its  Salts . 

Ammonia  from  soda  and  potassa. 

a.  The  salts  of  the  alkalies  to  be  separated  contain  the  same  vola-  3 
tile  acid , and  admit  of  the  total  expulsion  of  their  water  by  drying  at 
100°,  without  losing  ammonia  (e.  g .,  the  metallic  chlorides). 

Weigh  the  total  mass  of  the  salts  in  a platinum  crucible,  and 
heat  with  the  lid  on,  gently  at  first,  but  ultimately  for  some  time 
to  faint  redness ; let  the  mass  cool,  and  weigh.  The  decrease  of 
weight  gives  the  quantity  of  the  ammonia  salt.  If  the  acid  present 
is  sulphuric  acid,  you  must,  in  the  first  place,  take  care  to  heat  very 
gradually,  as  otherwise  you  will  suffer  loss  from  the  decrepitation 
of  the  sulphate  of  ammonia  ; and,  in  the  second  place,  bear  in  mind 
that  part  of  the  sulphuric  acid  of  the  sulphate  of  ammonia  remains 
with  the  sulphates  of  the  fixed  alkalies,  and  that  you  must  accord- 
ingly convert  them  into  neutral  salts,  by  ignition  in  an  atmosphere 
of  carbonate  of  ammonia,  before  proceeding  to  determine  their  weight 
(compare  §§  97  and  98).  Chloride  of  ammonium  cannot  be  separated 
in  this  manner  from  sulphates  of  the  fixed  alkalies,  as  it  converts 
them,  upon  ignition,  partly  or  totally  into  chlorides. 

b.  Some  one  or  other  of  the  conditions  given  in  a is  not  fulfilled. 

If  it  is  impracticable  to  alter  the  circumstances  by  simple  means  4 
so  as  to  make  the  method  a applicable,  the  fixed  alkalies  and  the 
ammonia  must  be  estimated  separately  in  different  portions  of  the 
substance.  The  portion  in  which  it  is  intended  to  determine  the 
soda  and  potassa  is  gently  ignited  until  the  ammonia  is  completely 
expelled.  The  fixed  alkalies  are  converted,  according  to  circum- 
stances, into  chlorides  or  sulphates,  and  treated  as  directed  in  \ or  5- 
The  ammonia  is  estimated,  in  another  portion,  according  to  § 99,  3. 


342 


SEPARATION, 


[§  152. 


3.  Indirect  Method. 

POTASSA  FROM  SODA. 

Convert  both  alkalies  into  chlorides  (§  97,  2),  and  weigh  ; estimate  5 
the  chlorine  (§  141)  ; and  calculate  the  quantities  of  the  soda  and 
potassa  from  these  data  (see  “ Calculation  of  Analyses,”  § 197). 

The  indirect  method  of  determining  potassa  and  soda  is  appli- 
cable [whenever  the  mixed  chlorides  can  be  obtained  in  a state  of 
purity.  It  is  very  accurate  and  expeditious*],  particularly  if  the 
chlorine  is  determined  volumetrically  (§  141,  I.,  b). 


Supplement  to  the  First  Group. 

Separation  of  Lithia  from  the  other  Alkalies. 

Lithia  may  be  separated  from  potassa  and  soda  in  the  indirect  6 
way,  or  by  either  of  the  following  two  methods  : — 

a.  Treat  the  nitrates  or  the  chlorides,  dried  at  120°,  with  a mix- 
ture of  equal  volumes  of  absolute  alcohol  and  anhydrous  ether,  digest 
at  least  for  twenty-four  hours,  with  occasional  shaking  (the  salts  must 
be  completely  disintegrated),  decanton  to  a filter,  and  treat  the  residue 
again  several  times  with  smaller  portions  of  the  mixture  of  alcohol  and 
ether.  Determine,  on  the  one  part,  the  undissolved  potassa  and  soda 
salts  ; on  the  other,  the  dissolved  lithia  salt,  by  distilling  the  fluid  off, 
and  converting  the  residue  into  sulphate.  This  method  is  apt  to  give  too 
much  lithium,  as  the  potassa  and  soda  salts,  especially  the  chlorides,  are 
not  absolutely  insoluble  in  a mixture  of  alcohol  and  ether.  The  results 
may  be  rendered  more  accurate  by  treating  the  impure  lithia  salt,  ob- 
tained by  distilling  off  the  ether  and  alcohol,  once  more  with  alcohol 
and  ether,  with  addition  of  a drop  of  nitric  or  hydrochloric  acid,  add- 
ing the  residue  left  to  the  principal  residue,  and  then  converting  the 
lithia  salt  into  sulphate.  If  the  salts,  which  it  is  intended  to  treat 
with  alcohol  and  ether,  have  been  ignited,  however  so  gently,  caustic 
lithia  is  formed — in  the  case  of  the  chloride  by  the  action  of  water — and 
carbonate  of  lithia  by  attraction  of  carbonic  acid  ; in  that  case,  it  is 
necessary,  therefore,  to  add  a few  drops  of  nitric,  or,  as  the  case  may 
be,  hydrochloric  acid,  in  the  process  of  digestion.  The  separation  of 
the  chlorides  of  the  alkali  metals  by  a mixture  of  ether  and  spirit 
was  originally  recommended  by  Rammelsberg.I 

If  we  have  to  separate  the  sulphates,  they  must  be  converted  into 
nitrates  or  chlorides  before  they  can  be  subjected  to  the  above  method. 
This  conversion  may  be  effected  by  one  of  the  processes  given  in  2* 
Instead  of  the  alcoholic  solution  of  chloride  of  strontium  you  may 
use  an  aqueous  solution  of  nitrate  of  strontia  with  addition  of  alcohol. 

b.  Weigh  the  mixed  alkalies,  best  in  form  of  sulphates,  and  then  deter-  7 
mine  the  lithia  as  phosphate  according  to  § 100.  If  the  quantity  of 
lithia  is  relatively  very  small,  convert  the  weighed  sulphates  into  chlo- 
rides (6),  separate,  in  the  first  place,  the  principal  amount  of  the  po- 
tassa and  soda  by  means  of  alcohol  (§  100),  and  then  determine  the 
lithia.  (Mayer  }). 


* Collier,  Am.  Jour.  Sci.  (2)  xxxvii.  344. 
f Pogg.  Annal.  66,  79 . % Anna!,  d.  Chem.  u.  Pharm.  98, 193. 


§ 153.] 


BASES  OF  GROUP  II. 


343 


The  separation  of  lithia  from  ammonia  may  be  effected  like  that  8 
of  potassa  and  soda  from  ammonia  (3  and  4)- 


SECOND  GROUP. 

BARYTA STRONTIA LIME MAGNESIA. 

I.  Separation  of  the  Oxides  of  the  Second  Group  from 

THOSE  OF  THE  FlRST. 

§ 153. 

Index : — The  Nos.  refer  to  those  in  the  margin. 

Baryta  from  potassa  and  soda,  9,  11. 
ii  u ammonia,  10. 

Strontia  from  potassa  and  soda,  9,  12. 

“ ‘k  ammonia,  10. 

Lime  from  potassa  and  soda,  9,  13. 

“ “ ammonia,  10. 

Magnesia  from  potassa  and  soda,  14 — 19. 

“ “ ammonia,  10. 

A.  General  Method. 

1.  The  whole  of  the  Alkaline  Earths  from  Potassa  and 
Soda. 

Principle:  Carbonate  of  ammonia  precipitates , from  a i solution  9 
containing  chloride  of  ammonium , only  baryta , strontia , and  lime. 

Mix  the  solution,  which  contains  the  bases  as  chlorides,  with  a suffi- 
cient quantity  of  chloride  of  ammonium  to  prevent  the  precipitation  of 
the  magnesia  by  ammonia ; dilute  considerably,  add  some  ammonia,  then 
carbonate  of  ammonia  in  slight  excess,  let  the  mixture  stand  covered  for 
2 hours  in  a warm  place,  filter,  and  wash  the  precipitate  with  water  to 
which  a few  drops  of  ammonia  have  been  added. 

The  precipitate  contains  the  baryta , strontia , and  lime;  the  filtrate 
the  magnesia  and  the  alkalies.  So  at  least  we  may  assume  in  cases 
where  the  highest  degree  of  accuracy  is  not  required.  Strictly  speaking, 
however,  the  solution  still  contains  exceedingly  minute  traces  of  lime 
and  somewhat  more  considerable  traces  of  baryta,  as  the  carbonates  of 
these  two  earths  are  not  absolutely  insoluble  in  a fluid  containing  chlo- 
ride of  ammonium  ; the  precipitate  also  may  contain  possibly  a little 
carbonate  of  ammonia  and  magnesia.  Treat  the  precipitate  according  to 
§ 154, and  the  filtrate — in  rigorous  analyses — as  follows:  add  3 or  4 
drops  (but  not  much  more)  of  dilute  sulphuric  acid,  then  oxalate  of  am- 
monia, and  let  the  fluid  stand  again  for  12  hours  in  a warm  place.  If  a 
precipitate  forms,  collect  this  on  a small  filter,  wash,  and  treat  on  the 
filter  with  some  dilute  hydrochloric  acid,  which  dissolves  the  oxalate  of 
lime,  and  leaves  the  sulphate  of  baryta  undissolved.  Since  a little  oxa- 
late of  magnesia  may  have  separated  with  the  former,  add  some  ammo- 
nia to  the  hydrochloric  solution,  filter  after  the  precipitate  has  settled, 
and  mix.  the  filtrate  with  the  principal  filtrate. 

Evaporate  the  fluid  containing  the  magnesia  and  the  alkalies  to  dry- 
ness, and  remove  the  ammonia  salts  by  gentle  ignition  in  a covered 


344 


SEPARATION". 


[§  153. 


crucible,  or  in  a small  covered  dish  of  platinum  or  porcelain.*  In  the 
residue,  separate  the  magnesia  from  the  alkalies  by  one  of  the  methods 
given  (14—19). 


2.  The  whole  of  the  Alkaline  Earths  from  Ammonia. — The  same  1 0 
principle  and  the  same  process  as  in  the  separation  of  potassa  and  soda 
from  ammonia  (3  and  4). 

B.  Special  Methods. 

Single  Alkaline  Earths  from  Potassa  and  Soda. 

1.  Baryta  from  Potassa  and  Soda. 

Precipitate  the  baryta  with  dilute  sulphuric  acid  (§  101, 1,  a),  evap- 1 1 
orate  the  filtrate  to  dryness,  and  ignite  the  residue,  with  addition  to- 
wards the  end  of  carbonate  of  ammonia  (§  97,  1 and  § 98,  1).  Take 
care  to  add  a sufficient  quantity  of  sulphuric  acid  to  convert  the  al- 
kalies also  completely  into  sulphates. 

This  method  is,  on  account  of  its  greater  accuracy,  preferable  to 
the  one  in  9,  in  cases  where  the  baryta  has  to  be  separated  only  from 
one  of  the  two  fixed  alkalies ; but  if  both  alkalies  are  present,  the 
other  method  is  more  convenient,  since  the  alkalies  are  then  obtained 
as  chlorides. 


2.  Strontia  from  Potassa  and  Soda. 

Strontia  may  be  separated  from  the  alkalies,  like  baryta,  by  means  1 2 
of  sulphuric  acid  ; but  this  method  is  not  preferable  to  the  one  in  9,  in 
cases  where  the  choice  is  permitted  (comp.  § 102). 

3.  Lime  from  Potassa  and  Soda. 

Precipitate  the  lime  with  oxalate  of  ammonia  (§  103,  2,  b , a),  evapo- 13 
rate  the  filtrate  to  dryness,  and  determine  the  alkalies  in  the  ignited 
residue.  In  determining  the  alkalies,  dissolve  the  residue,  freed  by 
ignition  from  the  ammonia  salts,  in  water,  filter  the  solution  from  the 
undissolved  portion,  acidify  the  filtrate,  according  to  circumstances, 
with  hydrochloric  acid  or  sulphuric  acid,  and  then  evaporate  to  dry- 
ness ; this  treatment  of  the  residue  is  necessary,  because  oxalate  of 
ammonia  partially  decomposes  chlorides  of  the  alkali  metals  upon 
ignition,  and  converts  the  bases  into  carbonates,  except  in  presence 
of  a large  proportion  of  chloride  of  ammonium.  The  results  are  still 
more  accurate  than  in  9,  except  where  oxalate  of  ammonia  has  been 
used,  after  the  precipitation  by  carbonate  of  ammonia,  to  remove  the 
minute  traces  of  lime  from  the  filtrate. 

4.  Magnesia  from  Potassa  and  SoDA.f 

a.  Methods  based  upon  the  sparing  solubility  of  Magnesia  in  Water. 

a.  Make  a solution  of  the  bases,  as  neutral  as  possible,  and  free  from  14 


* This  operation  effects  also  the  removal  of  the  small  quantity  of  sulphuric 
acid  added  to  precipitate  the  traces  of  baryta,  as  sulphates  of  the  alkalies  are 
converted  into  chlorides  of  the  alkali  metals  upon  ignition  in  presence  of  a large 
proportion  of  chloride  of  ammonium. 

f The  methods  a and  are  suitable  for  the  separation  of  magnesia  from  lithia. 


§ 163.] 


BASES  OF  GROUP  II. 


345 


ammonia  salts  (it  is  a matter  of  indifference  whether  the  acid  is  sul- 
phuric, hydrochloric,  or  nitric),  add  baryta- water  as  long  as  a pre- 
cipitate forms,  heat  to  boiling,  filter  and  wash  the  precipitate  with 
boiling  water.  The  precipitate  contains  the  magnesia  as  hydrate ; it 
is  dissolved  in  hydrochloric  acid,  the  baryta  thrown  down  with  sul- 
phuric acid,  and  the  magnesia  as  phosphate  of  magnesia  and  ammo- 
nia (§  104,  2).  The  alkalies,  which  are  contained  in  the  solution, 
according  to  circumstances,  as  chlorides,  nitrates,  or  caustic  alkalies, 
are  separated  from  the  baryta  as  directed  in  9 or  H.  The  method 
gives  good  results,  but  is  rather  tedious. 

j3.  Precipitate  the  solution  with  a little  pure  milk  of  lime,  boil,  15 
filter,  and  wash.  Separate  the  lime  and  the  magnesia  in  the  precipi- 
tate according  to  25  or  29  ; the  lime  and  the  alkalies  in.  the  filtrate, 
as  directed  in  9 or  13.  I am  very  fond  of  employing  this  method 
in  cases  where  the  magnesia  has  to  be  removed  from  a fluid  contain- 
ing lime  and  alkalies,  provided  the  alkalies  alone  are  to  be  deter- 
mined. 

y.  Add  to  the  chlorides  pure  oxalic  acid  in  sufficient  quantity  to  16 
convert  all  the  bases  present,  viewed  as  potassa,  into  quadroxalates  ; 
add  some  water,  evaporate  to  dryness  in  a platinum  dish,  and  ignite. 

By  this  operation  the  chlorides  of  the  alkali  metals  are  partially,  the 
chloride  of  magnesium  completely,  converted  into  oxalates,  which, 
upon  ignition,  give  carbonated  alkalies  and  magnesia.  Treat  the  resi- 
due repeatedly  with  small  quantities  of  boiling  water ; during  this 
washing  the  precipitate  may  be  transferred  to  the  filter  or  remain  in  the 
dish,  no  matter  which.  When  all  the  alkali  salt  is  washed  out,  dry  the 
filter,  burn  it  in  the  dish,  ignite  strongly,  and  weigh  the  magnesia.  If 
the  solution  looks  a little  turbid,  evaporate  to  dryness,  treat  the  resi- 
due with  water,  and  filter  off  the  trifling  amount  of  magnesia  still  re- 
maining ; add,  finally,  hydrochloric  acid  to  the  filtrate,  and  determine 
the  alkalies  as  chlorides. 

If  the  bases  are  present  in  form  of  sulphates,  add  to  the  boiling  17 
solution  chloride  of  barium,  until  the  formation  of  a precipitate  just 
ceases,  evaporate  the  filtrate  with  an  excess  of  oxalic  acid,  and  proceed 
as  in  10.  Separate  the  carbonate  of  baryta,  which  remains  mixed 
with  magnesia,  from  the  latter,  as  directed  22. 

We  owe  these  methods  to  Mitscherlich,  and  the  description  of  IB 
them  to  Lasch.*  I can  add  my  own  testimony  to  the  accuracy  of 
the  results.  Still  the  weighed  alkali  salt  should  always  be  tested 
with  phosphate  of  soda  and  ammonia  for  magnesia.  Usually  a weigh- 
able  precipitate  is  produced  which  cannot  be  passed  over. 

The  method  described  in  16  may  also  be  successfully  employed 
with  nitrates,  for  which  it  is,  indeed,  specially  recommended  by 
DEViLLE.f  Carbonic  acid  and  nitrous  acid  are  evolved  in  the  process 
of  evaporation. 

b.  Precipitation  of  Magnesia  as  Carbonate  of  Ammonia- 
Magnesia. 

Mix  the  solution  of  sulphates,  nitrates,  or  chlorides  (it  must  be  very  19 
concentrated)  with  an  excess  of  a concentrated  solution  of  sesquicarbo- 


* Joum.  f.  prakt.  Chem.  63,  343. 


f Ibid.  60, 17. 


346 


SEPARATION. 


[Se- 


nate of  ammonia  in  water  and  ammonia  (230  grm.  of  the  salt,  180 
c.  c.  solution  of  ammonia  sp.  gr.  0*92,  and  water  to  1 litre).  After 
twenty-four  hours  filter  off  the  precipitate  (MgO,  C02  4-  NH4  0,C02-f 
4 aq.),  wash  it  with  the  solution  of  caustic  and  carbonated  ammonia 
used  for  the  precipitation,  dry,  ignite  strongly  and  for  a sufficient 
length  of  time,  and  weigh  the  magnesia.  Evaporate  the  filtrate  to 
dryness,  keeping  the  heat  at  first  under  100°,  expel  the  ammonia 
salts,  and  determine  the  alkalies  as  chlorides  or  sulphates.  When  soda 
alone  is  present  the  results  are  satisfactory.  In  the  presence  of  potassa 
the  ignited  magnesia  must  be  extracted  with  water,  before  weigh- 
ing, as  it  contains  an  appreciable  quantity  of  carbonate  of  potassa ; 
the  washings  are  to  be  added  to  the  principal  filtrate.  This  last  mea- 
sure is  unnecessary  in  the  absence  of  potassa.  Results  satisfactory ; 
the  magnesia  is  a little  too  low.  Mean  error  TqVo  (F.  G.  Schaff- 
gotsch,*  H.  Weber f). 


II.  Separation  of  the  Oxides  of  the  Second  Group  from 

EACH  OTHER. 

§ 154. 

Index  : — The  Nos.  refer  to  those  in  the  margin. 

Baryta  from  strontia,  21,  24,  32. 

“ lime,  21,  23,  24,  32. 

“ magnesia,  20,  22. 

Strontia  from  baryta,  21,  24,  32. 

“ lime,  28,  31. 

“ magnesia,  20,  22, 

Lime  from  baryta,  21,  23,  24,  32. 

“ strontia,  28,  31. 

“ magnesia,  20,  25,  26,  27,  29,  30. 

Magnesia  from  baryta,  20,  22. 

“ strontia,  20,  22. 

“ lime,  20,  25,  26,  27,  29,  30. 

A.  General  Method. 

THE  WHOLE  OF  THE  ALKALINE  EARTHS  FROM  EACH  OTHER. 

Proceed  as  in  9-  The  magnesia  is  precipitated  from  the  filtrate  20 
with  phosphate  of  soda.  The  precipitated  carbonates  of  the  baryta, 
strontia,  and  lime,  are  dissolved  in  hydrochloric  acid,  and  the  bases 
separtaed  as  directed  in  21*  The  traces  of  magnesia,  which  may  be 
present  in  the  carbonate  of  ammonia  precipitate,  are  obtained  by  eva- 
porating the  filtrate  from  the  sulphate  of  strontia  or  lime  to  dryness, 
taking  up  the  residue  with  water  and  precipitating  the  solution  with 
phosphate  of  soda  and  ammonia. 

B.  Special  Methods. 

1.  Methods  based  upon  the  Insolubility  of  Silicojluoride  of 
JBarium. 

Baryta  from  Strontia  and  from  Lime. 

Mix  the  neutral  or  slightly  acid  solution  with  hydrofluosilicic  acid  J 21 


* Pogg.  Annal.  104,  482.  f Vierteljahrsschrift  f.  prakt.  Pharm.  8,  161. 
X If  not  kept  in  a gutta-percha  bottle  it  should  be  freshly  prepared. 


BASES  OF  GROUP  II. 


347 


§ 154.1 


in  excess,  add  a volume  of  spirit  of  wine  equal  or  somewhat 
inferior  to  that  of  the  fluid  (H.  Rose),  let  the  mixture  stand  twelve 
hours,  collect  the  precipitate  of  silicojluoride  of  barium  on  a 
weighed  filter,  wash  with  a mixture  of  equal  parts  of  water  and 
spirit  of  wine,  until  the  washings  cease  to  show  even  the  least  trace 
of  acid  reaction  (but  no  longer),  and  dry  at  100°.  Precipitate  the 
strontia  or  lime  from  the  filtrate  by  dilute  sulphuric  acid  (§  102,  1, 
a,  and  § 103,  1,  a).  The  results  are  satisfactory.  For  the  pro- 
perties of  silicofluoride  of  barium,  see  § 71.  If  both  strontia  and 
lime  are  present,  the  sulphates  are  weighed,  converted  into  car- 
bonates (§  132,  II.,  5),  and  the  two  bases  then  separated  as  directed 

in  31. 


2.  Methods  based  upon  the  Insolubility  of  Sulphate  of  Baryta , 

or  Sulphate  of  Strontia , as  the  case  may  be , in  water  and 
in  Solution  of  Hyposulphite  of  Soda. 

a.  Baryta  and  Strontia  from  Magnesia. 

Precipitate  the  baryta  and  strontia  with  sulphuric  acid  (§  101,  1,22 
a,  and  § 102,  1,  a),  and  the  magnesia  from  the  filtrate  with  phosphate 
of  soda  and  ammonia  (§  104,  2). 

b.  Baryta  from  Lime. 

Mix  the  solution  with  hydrochloric  acid,  then  with  highly  dilute  23 
sulphuric  acid  (1  part  acid  to  300  water),  as  long  as  a precipitate 
forms  ; allow  to  deposit,  and  determine  the  sulphate  of  baryta  as 
directed  in  § 101,  1,  a.  Concentrate  the  washings  by  evaporation, 
and  add  them  to  the  filtrate,  neutralize  the  acid  with  ammonia,  and 
precipitate  the  lime  as  oxalate  (§  103,  2,  5,  a).  The  method  is  prin- 
cipally to  be  recommended  when  small  quantities  of  baryta  have  to 
be  separated  from  much  lime.  If  we  have  to  separate  sulphate  of 
lime  from  sulphate  of  baryta  the  salts  may  (in  the  absence  of  free 
acids)  be  treated  repeatedly  with  a solution  of  hyposulphite  of  soda 
at  a gentle  heat.  The  sulphate  of  baryta  remains  undissolved,  the 
sulphate  of  lime  dissolves.  The  lime  is  precipitated  from  the  filtrate 
by  oxalate  of  ammonia  (Diehl*). 

3.  Method  based  upon  the  different  deportment  with  Carbonated 

Alkalies  ofm  Sulphate  of  Baryta  on  the  one  hand , and 
Sulphates  of  Strontia  and  Lime  on  the  other. 

Baryta  from  Strontia  and  lime. 

Digest  the  precipitated  sulphates  of  the  three  bases  for  twelve  24 
hours,  at  the  common  temperature  (15 — 20°),  with  frequent  stirring, 
with  a solution  of  carbonate  of  ammonia,  decant  the  fluid  on  to  a 
filter,  treat  the  residue  repeatedly  in  the  same  way,  wash  finally  with 
water,  and  in  the  still  moist  precipitate,  separate  the  undecomposed 
sulphate  of  baryta  by  means  of  cold  dilute  hydrochloric  acid  from 
the  carbonates  of  strontia  and  lime  formed.  To  hasten  the  separa- 
tion you  may  boil  the  sulphates  for  some  time  with  a solution  of 
carbonate  of  potassa  (not  soda),  to  which  ^ the  amount  of  the  car- 


* Journ.  f.  prakt.  Chem.  79,  30. 


348 


SEPARATION. 


[§  154. 


bonate,  or  more,  of  sulphate  of  potassa  has  been  added.  By  this 
process  also  the  sulphates  of  strontia  and  lime  are  decomposed,  the 
sulphate  of  baryta  remaining  unacted  on.  If  the  bases  are  in  solu- 
tion, the  above  solution  of  carbonate  and  sulphate  of  potassa  is 
added  in  excess  at  once,  and  the  whole  boiled.  The  precipitate,  con- 
sisting of  sulphate  of  baryta  and  carbonates  of  strontia  and  lime,  is 
to  be  treated  as  above  with  cold  hydrochloric  acid  (H.  Bose  *). 

4.  Method  based  on  the  Insolubility  of  Sulphate  of  Lime  in 
Alcohol. 

[Lime  from  Magnesia. 

a.  Evaporate  the  hydrochloric  solution  nearly  to  dryness,  treat  25 
the  residue  with  strong  alcohol  until  it  is  dissolved.  Add  to  the 
solution  a slight  excess  of  concentrated  sulphuric  acid  and  let  stand 
several  hours.  The  precipitate,  containing  all  the  lime  and  some  of 
the  magnesia  as  sulphates,  is  transferred  to  a filter  with  the  aid  of 
strong,  nearly  absolute,  alcohol  and  washed  with  the  same  until  the 
washings  cease  to  react  acid  to  test  paper.  After  all  free  acid  is  thus 
removed,  continue  the  washing  with  alcohol  of  35 — 40  per  cent,  as 
long  as  any  solid  matters  are  extracted.  The  lime  all  remains  on  the 
filter  and  is  weighed  as  sulphate,  the  magnesia  is  all  found  in  the 
filtrate  and  washings,  from  which,  after  evaporating  oft'  the  alcohol, 

it  is  thrown  down  as  ammonio-phosphate.  Excellent  method  (A. 

CHIZYNSKlf  ).] 

b.  Small  quantities  of  Lime  from  much  Magnesia.  Convert  26 
the  bases  into  neutral  sulphates,  dissolve  the  mass  in  water,  and  add 
alcohol  with  constant  stirring,  till  a slight  permanent  turbidity  is 
produced.  Wait  a few  hours  and  then  filter,  wash  the  precipitated 
sulphate  of  lime  with  alcohol,  which  has  been  diluted  with  an  equal 
volume  of  water,  and  determine  it  after  § 103,  1,  a (in  which  case 
the  weighed  sulphate  must  be  tested  for  magnesia),  or  dissolve  the 
precipitate  in  water  containing  hydrochloric  acid  and  separate  the 
lime  from  the  small  quantity  of  magnesia  possibly  coprecipitated 
according  to  29  (Scheerer|). 

[c.  In  presence  of  phosphoric  acid,  evaporate  the  hydrochloric  27 
acid  solution  to  dryness,  add  strong  alcohol  to  the  residue,  then  mode- 
rately strong  sulphuric  acid,  and  treat  as  in  a.  The  lime  is  separated 
as  pure  sulphate.  The  filtrate,  after  evaporating  of  the  alcohol,  is 
divided  into  two  portions.  In  one  magnesia  is  precipitated  by  addi- 
tion of  chloride  of  ammonium,  ammonia,  and  phosphate  of  soda 
(§  104,  2) ; from  the  other  throw  down  phosphoric  acid  by  means  of 
magnesia  solution  (§  134,  5,  a).] 

i 5.  Method  based  on  the  Insolubility  of  Sulphate  of  Strontia  in 
Solution  of  Sulphate  of  Ammonia. 

Strontia  from  Lime.  If  the  mixture  is  soluble,  dissolve  in  the  28 
smallest  quantity  of  water,  add  about  50  times  the  quantity  of  the 
substance  of  sulphate  of  ammonia  dissolved  in  four  times  its  weight 
of  water,  and  either  boil  for  some  time  with  renewal  of  the  water  that 
evaporates  and  addition  of  a very  little  ammonia  (as  the  solution  of 
sulphate  of  ammonia  becomes  acid  on  boiling),  or  allow  to  stand  at 

* Pogg.  Annal.  xcv.  286,  299,  427.  f Fres.  Zeitschrift,  iv.  348. 

X Annal.  d.  Chem.  u.  Pharm.  110,  237. 


154.J 


BASES  OF  GROUP  II. 


349 


the  ordinary  temperature  for  twelve  hours.  Filter  and  wash  the  pre- 
cipitate, which  consists  of  sulphate  of  strontia  and  a little  sulphate  of 
strontia  and  ammonia  with  a concentrated  solution  of  sulphate  of  am- 
monia till  the  washings  remain  clear  on  addition  of  oxalate  of  am- 
monia. The  precipitate  is  cautiously  ignited,  moistened  with  a little 
dilute  sulphuric  acid  (to  convert  the  small  quantity  of  sulphide  of 
strontium  into  sulphate),  and  weighed.  The  highly  dilute  filtrate  is 
precipitated  with  oxalate  of  ammonia,  and  the  lime  determined  ac- 
cording to  § 103,  2,  b , a.  If  you  have  the  solid  sulphates  to  analyze, 
they  are  very  finely  powdered  and  boiled  with  concentrated  solution 
of  sulphate  of  ammonia  with  renewal  of  the  evaporated  water  and  addi- 
tion of  a little  ammonia.  Results  very  close,  e.r/.,  T048  SrO,  N05 
instead  of  1*053,  and  0*497  CaO,  C0.2,  instead  of  0*504  (H.  Rose*). 

6.  Methods  based  upon  the  Insolubility  of  Oxala,ie  of  lime  in 
Chloride  of  Ammonium  and  in  Acetic  Acid. 

Lime  from  Magnesia. 

a.  Mix  the  properly  diluted  solution  with  sufficient  chloride  of  am-  29 
monium  to  prevent  the  formation  of  a precipitate  by  ammonia,  which 
is  added  in  slight  excess ; and  oxalate  of  ammonia  as  long  as  a preci- 
pitate forms,  then  a further  portion  of  the  same  reagent,  about  suffi- 
cient to  convert  the  magnesia  also  into  oxalate  (which  remains  in  solu- 
tion). This  excess  is  absolutely  indispensable  to  insure  complete  precip- 
itation  of  the  lime,  as  oxalate  of  lime  is  slightly  soluble  in  solution  of 
chloride  of  magnesium  not  mixed  with  oxalate  of  ammonia  (Expt. 

No.  92).  Let  the  mixture  stand  twelve  hours  in  a moderately  warm 
place,  decant  the  supernatant  clear  fluid,  as  far  as  practicable,  from 
the  precipitated  oxalate  of  lime,  mixed  with  a little  oxalate  of  mag- 
nesia, on  to  a filter,  wash  the  precipitate  once  in  the  same  way  by  de- 
cantation, then  dissolve  in  hydrochloric  acid,  add  water,  then  ammo- 
nia in  slight  excess,  and  a little  oxalate  of  ammonia.  Let  the  fluid 
stand  until  the  precipitate  has  completely  subsided,  then  pour  on  to 
the  previous  Alter,  transfer  the  precipitate  finally  to  the  latter,  and 
proceed  exactly  as  directed  § 103,  2,  5,  a.  The  first  filtrate  contains 
the  larger  portion  of  the  magnesia,  the  second  the  remainder.  Evap- 
orate the  second  filtrate,  acidified  with  hydrochloric  acid,  to  a small 
volume,  then  mix  the  two  fluids,  and  precipitate  the  magnesia  with 
phosphate  of  soda  as  directed  § 104,  2.  If  the  quantity  of  ammonia 
salts  present  is  considerable,  the  estimation  of  the  magnesia  is  ren- 
dered more  accurate  by  evaporating  the  fluids,  in  a large  platinum  or 
silver  dish,f  to  dryness,  and  igniting  the  residuary  saline  mass,  in 
small  portions  at  a time,  in  a smaller  platinum  dish,  until  the  ammo- 
nia salts  are  expelled.  The  residue  is  then  treated  with  hydrochloric 
acid  and  water,  heat  applied,  the  fluid  filtered  J and  finally  precipitated 
with  ammonia  and  phosphate  of  soda. 

Numerous  experiments  have  convinced  me  that  this  method,  which 
is  so  frequently  employed,  gives  accurate  results  only  if  the  foregoing 
instructions  are  strictly  complied  with.  It  is  only  in  cases  where  the 


* Pogg.  Annal.  110,  296. 

f A porcelain  dish  does  not  answer  so  well  (see  Expt.  No.  3). 

X If  the  process  of  evaporation  has  been  conducted  in  a silver  vessel,  a little 
chloride  of  silver  will  often  separate. 


350 


SEPARATION. 


quantity  of  magnesia  present  is  relatively  small,  that  a single  precipi- 
tation with  oxalate  of  ammonia  may  be  found  sufficient  (comp.  Expt. 

No.  93). 

b.  In  the  case  of  lime  and  magnesia  combined  with  phosphoric  30 
acid,  dissolve  in  the  least  possible  quantity  of  hydrochloric  acid,  add 
ammonia  until  a copious  precipitate  forms ; redissolve  this  by  addi- 
tion of  acetic  acid,  and  precipitate  the  lime  from  the  solution  with 
an  excess  of  oxalate  of  ammonia.  To  determine  the  magnesia,  pre- 
cipitate the  filtrate  with  ammonia  and  phosphate  of  soda.  As  free 
acetic  acid  by  no  means  prevents  the  precipitation  of  small  quantities 
of  oxalate  of  magnesia,  the  precipitate  contains  some  magnesia,  and, 
as  oxalate  of  lime  is  not  quite  insoluble  in  acetic  acid,  the  filtrate 
contains  some  lime ; these  two  sources  of  error  compensate  each  other 
in  some  measure.  Inaccurate  analyses,  however,  these  trifling  admix- 
tures of  magnesia  and  lime  are  afterwards  separated  from  the  weighed 
precipitates  of  carbonate  of  lime  and  pyrophosphate  of  magnesia  re- 
spectively. 

7.  Indirect  Method. 

Strontia  from  Lime. 

Determine  both  bases  first  as  carbonates,  precipitating  them  either  31 
with  carbonate  or  with  oxalate  of  ammonia  (§§  102,  103) ; then  esti- 
mate the  amount  of  carbonic  acid  in  them,  and  calculate  the  amount 
of  strontia  and  of  lime  as  directed  in  § 197.  The  determination  of 
the  carbonic  acid  may  be  effected  by  fusion  with  vitrified  borax 
(§  139,  II.,  c),  but  the  application  of  a moderate  white  heat,  such  as 
is  given  by  a good  gas  blast-lamp  without  the  use  of  a crucible  jacket, 
is  alone  sufficient  to  drive  out  all  the  carbonic  acid  from  both  the 
carbonates  (F.  G.  Schaffgotsch  *).  I can  strongly  recommend  this 
method.  It  is  well  to  precipitate  the  carbonates  hot,  to  press  the  pre- 
cipitate cautiously  down  in  the  platinum  crucible  and  turn  over  the 
agglomerated  cake  every  now  and  then  till,  after  repeated  ignitions, 
the  weight  has  become  constant.  The  results  are  good,  if  neither  of 
the  bases  is  present  in  too  minute  quantity. 

The  indirect  separation  may  of  course  be  effected  by  means  of  32 
other  salts,  and  can  be  used  also  for  the  determination  of  lime  in 
PRESENCE  OF  BARYTA  Or  of  BARYTA  IN  PRESENCE  OF  STRONTIA.  In  the 
expulsion  of  carbonic  acid  from  carbonate  of  baryta  vitrified  borax 
must  be  used  (§  139,  II.,  c). 

THIRD  GROUP. 

Alumina — Sesquioxide  of  Chromium. 

I.  Separation  of  the  Oxides  of  the  Third  Group  from 
the  Alkalies. 

§ 155. 

1.  From  Ammonia. 

a.  Salts  of  alumina  and  of  sesquioxide  of  chromium  may  be  33 
separated  from  salts  of  ammonia  by  ignition.  However,  in  the 


Pogg.  Annal.  113,  615. 


156. 


BASES  OF  GROUP  III. 


351 


case  of  alumina,  this  method  is  applicable  only  in  the  absence  of 
chlorine  (volatilization  of  chloride  of  aluminium).  The  safest  way, 
therefore,  is  to  mix  the  compound  with  carbonate  of  soda  before 
igniting. 

b.  Determine  the  ammonia  by  one  of  the  methods  given  in  § 99,  3,34 
using  solution  of  potassa  or  soda  to  effect  the  expulsion  of  the  am- 
monia. The  alumina  and  sesquioxide  of  chromium  are  then  deter- 
mined in  the  residue  in  the  same  way  as  in  35- 

2.  From  Potassa  and  Soda. 

a.  Precipitate  and  determine  the  sesquioxide  of  chromium  and  35 
alumina  as  directed  in  § 105,  a,  and  § 106,  a.  The  filtrate  contains 
the  alkalies,  which  are  then  freed  from  the  salt  of  ammonia  formed, 
by  evaporation  to  dryness  and  ignition. 

b.  Alumina  maybe  separated  also  from  potassa  and  soda,  by  heat-  36 
ing  the  nitrates  (see  38). 

II.  Separation  of  the  Oxides  of  the  Third  Group  from  the 
Alkaline  Earths. 

§156. 

Index : — The  Nos.  refer  to  those  in  the  margin. 

Alumina  from  baryta,  37,  42,  43. 

strontia,  37,  42,  43. 

“ lime,  37,  42,  44,  45,  46. 

“ magnesia,  37,  42,  45,  46. 

Sesquioxide  of  chromium  from  the  alkaline  earths,  47,  48. 

Separation  of  Alumina  from  the  Alkaline  Earths. 

A.  General  Methods. 

The  whole  of  the  Alkaline  Earths  from  Alumina. 

1.  Precipitation  of  Alumina  by  Ammonia , and  its  Solution  in 
Soda. 

Mix  the  moderately  dilute  hot  solution  (preferably  in  a platinum  37 
dish)  with  a tolerable  quantity  of  chloride  of  ammonium,  if  such  be  not 
already  present,  add  ammonia  in  moderate  excess,  and  boil  till  no 
more  free  ammonia  is  observable.  Under  these  circumstances,  a little 
magnesia,  and  also  a small  quantity  of  carbonate  of  lime,  baryta,  or 
strontia  are  at  first  precipitated  along  with  the  alumina  ; on  the  boil- 
ing with  chloride  of  ammonium,  the  coprecipitated  alkaline  earths  re- 
dissolve, so  that  the  alumina  finally  retains  only  an  unweighable  or 
scarcely  weighable  trace  of  magnesia.  Allow  to  deposit,  and  proceed 
with  the  alumina  determination  according  to  § 105,  a.  After  it  has 
been  weighed  fuse  it  for  a long  time  with  bisulphate  of  potassa,  dis- 
solve the  fused  mass  in  water,  and  determine  any  silicic  acid  * that 
may  remain.  The  solution,  when  mixed  with  potassa  in  excess,  will 
not  appear  perfectly  clear,  but  will  contain  a few  flocks  of  magnesia. 

If  there  is  any  amount  of  the  latter,  filter  it  off,  dissolve  in  nitric  acid, 

* A small  quantity  will  always  be  found  if  you  have  boiled  in  a glass  or  por* 
celain  vessel. 


352 


SEPARATION. 


[§  156. 


precipitate  with  ammonia,  boil  till  the  fluid  ceases  to  smell  of  am- 
monia, filter,  evaporate  the  small  quantity  of  fluid  in  a platinum  cap- 
sule, ignite,  weigh  the  residual  magnesia,  deduct  it  from  the  alumina 
and  add  it,  on  the  other  hand,  to  the  principal  quantity  of  the  mag- 
nesia. In  order  to  the  further  separation  of  the  alkaline  earths, 
acidify  the  fluid  containing  them  with  hydrochloric  acid,  evaporate 
(preferably  in  a platinum  dish)  to  a small  bulk,  and  while  still  warm 
add  ammonia  just  in  excess.  A small  precipitate  of  alumina  is  some- 
times formed  at  this  stage  ; filter  off,  wash  and  weigh  with  the  prin- 
cipal precipitate.  In  the  filtrate  determine  the  alkaline  earths  ac- 
cording to  § 154. 

2.  Unequal  Decomposahility  of  the  Nitrates  at  a Moderate  Heat 

(Deville*). 

To  make  this  simple  and  convenient  method  applicable,  the  bases  38 
must  be  present  as  pure  nitrates.  Evaporate  to  dryness  in  a plati- 
num dish,  and  heat  gradually,  with  the  cover  on,  in  the  sand-  or  air- 
bath — or,  better  still,  on  a thick  iron  disk,  with  two  cavities,  one  for 
the  platinum  dish,  the  other,  filled  with  brass  filings,  for  the  thermo- 
meter— to  from  200°  to  250°,  until  a glass  rod  moistened  with  am- 
monia ceases  to  indicate  further  evolution  of  nitric  acid  fumes.  You 
may  also,  without  risk,  continue  to  heat  until  nitrous  acid  vapors 
form.  The  residue  consists  of  alumina,  nitrates  of  baryta,  strontia, 
and  lime,  and  nitrate  and  basic  nitrate  of  magnesia. 

Moisten  the  mass  with  a concentrated  solution  of  nitrate  of  am- 
monia, and  heat  gently,  but  do  not  evaporate  to  dryness.  Repeat  this 
operation  until  no  further  evolution  of  ammonia  is  perceptible.  (The 
basic  nitrate  of  magnesia,  insoluble  in  water,  dissolves  in  nitrate  of 
ammonia,  with  evolution  of  ammonia,  as  neutral  nitrate  of  magnesia.) 
Add  water,  and  digest  at  a gentle  heat. 

If  the  nitrate  of  ammonia  has  evolved  only  imperceptible 
traces  of  ammonia,  pour  hot  water  into  the  dish,  stir,  and  add  a 
drop  of  dilute  ammonia;  this  must  cause  no  turbidity  in  the 
fluid  ; should  the  fluid  become  turbid,  this  proves  that  the  heat- 
ing of  the  nitrates  has  not  been  continued  long  enough  ; in  which 
case  you  must  again  evaporate  the  contents  of  the  dish,  and  heat 
once  more. 

The  alumina  remains  undissolved  in  the  form  of  a dense  granular 
substance.  Decant  after  digestion,  and  wash  with  boiling  water ; 
ignite  strongly  in  the  same  vessel  in  which  the  separation  has  been 
effected,  and  weigh.  Separate  the  alkaline  earths  as  directed  § 154. 

In  the  same  way  alumina  may  be  separated  also  from  potassa  and 
soda. 

3.  Method  in  which  the  processes  of  1 and  2 are  combined. 

Precipitate  the  alumina  as  in  37?  wash  in  the  same  way  as  there  39 

directed,  then  treat  while  still  moist  with  nitric  acid,  and  proceed  ac- 
cording to  38  to  remove  the  trifling  amount  of  magnesia,  &c.,  copreci- 
pitated ; add  the  solution  obtained  to  the  principal  solution  of  the 
alkaline  earths,  and  treat  the  fluid  as  directed  in  37.  This  method 
may  be  employed  also  in  the  case  of  chlorides ; it  will  be  sometimes 
found  useful. 


Joum.  f.  prakt.  Chem.  1853,  60,  9. 


156.] 


BASES  OF  GROUP  III. 


353 


4.  Precipitation  of  Alumina  by  Acetate  or  Formiate  of  Soda 

upon  boiling. 

The  same  process  as  for  the  separation  of  sesquioxide  of  iron  from  40 
the  alkaline  earths.  The  method  is  employed  more  particularly  when 
both  alumina  and  sesquioxide  of  iron  have  to  be  separated  from  alka- 
line earths  at  the  same  time  (§  113,  1,  d). 

5.  Precipitation  of  Alumina  by  Succinate  of  Ammonia. 

Proceed  as  for  the  precipitation  of  sesquioxide  of  iron  b}7-  the  same  41 

reagent  (§  113,  1,  c ) ; especially  to  be  employed,  when  alumina  and 
sesquoixide  of  iron  are  both  to  be  separated  from  alkaline  earths  at 
the  same  time. 

B.  Special  Methods. 

Some  of  the  Alkaline  Earths  from  Alumina. 

1.  Precipitation  of  some  of  the  Salts  of  the  Alkaline  Earths. 

a.  Baryta  and  Strontia  from  Alumina. 

Precipitate  the  baryta  and  strontia  with  sulphuric  acid  (§§  101  43 
and  102),  and  the  alumina  from  the  filtrate  as  directed  § 105,  a.  This 
method  is  especially  suited  for  the  separation  of  baryta  from  alumina. 

b.  Lime  from  Alumina. 

Add  ammonia  to  the  solution  until  a permanent  precipitate  forms,  44 
then  acetic  acid  until  this  precipitate  is  redissolved,  then  acetate  of 
ammonia,  and  finally  oxalate  of  ammonia  in  slight  excess  (§  103,  2, 
b,  p ) ; allow  the  precipitated  oxalate  of  lime  to  deposit  in  the  cold, 
then  filter,  and  precipitate  the  alumina  from  the  filtrate  as  directed 
8 105,  a.  In  presence  of  oxalate  of  ammonia,  alumiifa  requires  some 
time  for  precipitation  (Pisani). 

c.  Magnesia  and  small  quantities  of  Lime  from  Alumina. 

Mix  with  some  tartaric  acid,  supersaturate  with  ammonia  and  45 

from  the  clear  fluid  (in  the  presence  of  enough  alumina  no  tartrate  of 
lime  is  precipitated)  precipitate  first  the  lime  by  oxalate  of  ammonia, 
then  the  magnesia  by  phosphate  of  soda.  If  the  alumina  is  to  be 
determined  in  the  filtrate,  the  latter  must  be  evaporated  with  addi- 
tion of  carbonate  of  soda  and  nitre  to  dryness,  the  residue  ignited, 
softened  with  water,  dissolved  in  hydrochloric  acid  (not  in  the  pla- 
tinum dish),  and  the  alumina  precipitated  by  ammonia.  The  am- 
monio-phosphate  of  magnesia  which  may  contain  basic  tartrate  of 
magnesia  is  to  be  dissolved  in  hydrochloric  acid,  reprecipitated  with 
ammonia,  then  dried  and  weighed.  [Not  applicable  when  alumina 
is  present  in  large  proportion,  since  alumina  salts  dissolve  ammonio- 
phosphate  of  magnesia  (Knapp).] 

2.  Precipitation  of  Alumina  by  Carbonate  of  Paipta. 

Alumina  from  Magnesia,  and  small  quantities  of  Lime. 

Mix  the  slightly  acid  dilute  fluid  in  a flask,  with  carbonate  of  48 
baryta  (shaken  up  with  water),  in  moderate  excess  ; cork  the  flask 
and  let  the  mixture  stand  in  the  cold  until  the  hydrated  alumina 
has  subsided,  wash  by  decantation  three  times,  filter,  and  then  de- 
termine the  alumina  in  the  precipitate  as  directed  43  j in  the  fil- 

23 


354 


SEPARATION. 


[8  w- 


trate,  first  precipitate  the  baryta  by  sulphuric  acid  (23),  and  then 
separate  the  lime  and  magnesia  according  to  § 154. 

Separation  of  Sesquioxide  of  Chromium  from  the  Alkaline 
Earths. 

The  best  way  to  effect  the  separation  of  sesquioxide  of  chromium  47 
from  the  alkaline  earths  at  the  same  time,  is  to  convert  the  ses- 
quioxide into  chromic  acid.  For  this  purpose  the  pulverized  sub- 
stance is  mixed  with  2|-  parts  of  pure  carbonate  of  soda  and  2£ 
parts  of  nitrate  of  potassa,  and  the  mixture  heated  in  a platinum 
crucible  to  fusion.  On  treating  the  fused  mass  with  hot  water,  the 
chromium  dissolves  as  alkaline  chromate ; the  residue  contains  the 
alkaline  earths  as  carbonates,  or  in  the  caustic  state  (magnesia). 

The  chromium  in  the  solution  is  determined  as  directed  § 130. 

I need  hardly  observe  that  sesquioxide  of  chromium  may  also  be  48 
separated  from  baryta  and,  though  less  perfectly,  from  strontia , by 
means  of  sulphuric  acid  added  to  the  acid  solution  of  the  substance. 
Sesquioxide  of  chromium  cannot  be  separated  by  ammonia  from  the 
alkaline  earths,  since,  even  though  carbonic  acid  be  completely  ex- 
cluded, particles  of  the  alkaline  earths  are  thrown  down  with  the 
sesquioxide  of  chromium.  From  solutions  containing  a salt  of  ses- 
quioxide of  chromium,  lime  cannot  be  precipitated  completely  by 
oxalate  of  ammonia ; but  it  may  be  by  sulphuric  acid  and  alcohol 

(§  103,  1). 

III.  Separation  of  Sesquioxide  of  Chromium  from  Alumina. 

§ 157. 

a.  Fuse  the  oxides  with  2 parts  by  weight  of  nitrate  of  potassa  and  49 
4 parts  of  carbonate  of  soda,  in  a platinum  crucible,  treat  the  fused 
mass  with  boiling  water,  rinse  the  contents  of  the  crucible  into  a 
porcelain  dish  or  beaker,  add  a somewhat  large  quantity  of  chlorate 

of  potassa,  supersaturate  slightly  with  hydrochloric  acid,  evaporate  to 
the  consistence  of  syrup,  and  add,  during  the  latter  process,  some  more 
chlorate  of  potassa  in  portions,  to  remove  the  free  hydrochloric  acid. 
Dilute  now  with  water,  and  precipitate  the  alumina  by  carbonate  of 
ammonia  or  ammonia  as  directed  in  § 105,  a.  The  alumina  falls  down 
free  from  sesquioxide  of  chromium.  In  the  filtrate  the  chromium  is 
determined  as  directed  § 1 30.  If  you  omit  the  evaporation  with  hydro- 
chloric acid  and  chlorate  of  potassa,  part  of  the  chromic  will  be  reduced 
by  the  nitrous  acid  in  the  fluid,  and  sesquioxide  of  chromium  will 
accordingly,  upon  addition  of  ammonia,  precipitate  with  the  alumina 
(Dexter*). 

b.  Dissolve  the  oxides  in  hydrochloric  acid  [make  the  solution  50 
nearly  neutral  by  carbonate  of  soda,  add  acetate  of  soda  in  excess],  and 
saturate  the  solution  with  chlorine  gas.  The  sesquioxide  of  chromi- 
um will  be  converted  {into  chromic  acid,  and  the  alumina  partially  sep- 
arated. When  the  fluid  has  become  of  a pure  yellow  color,  heat  to 
remove  the  excess  of  chlorine,  add  carbonate  of  ammonia,  and  digest 

to  destroy  the  hypochlorous  acid  and  precipitate  the  still  dissolved 
alumina,  filter  off  the  alumina,  and  determine  it  according  to  § 105, 


DPogg.  .Anna!  89,  142. 


BASES  OF  GROUP  IV. 


355 


§ 158.] 

a.  In  the  fluid  the  chromium  is  determined  according  to  § 130,  I.,  a. 
(Wohler,*  [Gibbs]|). 


FOURTH  GROUP. 

OXIDE  OF  ZINC PROTOXIDE  OF  MANGANESE PROTOXIDE  OF  NICKEL 

PROTOXIDE  OF  COBALT PROTOXIDE  OF  IRON SESQUIOXIDE  OF  IRON 

(SESQUIOXIDE  OF  URANIUM). 

I.  Separation  of  the  Oxides  of  the  Fourth  Group  from  the 

Alkalies. 

§ 158. 

A.  General  Methods. 

1.  All  the  Oxides  of  the  Fourth  Group  from  Ammonia. 

Proceed  as  for  the  separation  of  sesquioxide  of  chromium  and  alu-  51 
mina  from  ammonia,  33*  It  must  be  borne  in  mind  that  the  oxides 
of  the  fourth  group  comport  themselves,  upon  ignition  with  chloride 
of  ammonium,  as  follows  : Sesquioxide  of  iron  is  partly  volatilized  as 
sesquichloride  ; the  oxides  of  manganese  are  converted  into  proto- 
chloride of  manganese,  containing  protosesquioxide  of  that  metal ; the 
oxides  of  nickel  and  cobalt  are  reduced  to  the  metallic  state  ; oxide  of 
zinc  volatilizes,  with  access  of  air,  as  chloride  of  zinc  (H.  Rose).  It 
is,  therefore,  generally  the  safest  way  to  add  carbonate  of  soda.  The 
ammonia  is  determined  in  a separate  portion. 

2.  All  Oxides  of  the  Fourth  Group  from  Potassa  and  Soda. 

Mix  the  solution  in  a flask  with  chloride  of  ammonium  if  necessary,  52 
add  ammonia  till  neutral  or  slightly  alkaline,  then  yellow  sulphide  of 
ammonium  saturated  with  sulphuretted  hydrogen,  fill  the  flask  nearly 
to  the  top  with  water,  cork  it,  allow  the  precipitated  sulphides  to 
subside,  and  then  filter  them  off  from  the  fluid  containing  the  alka- 
lies. In  performing  this  process  the  precautionary  rules  given  under 
the  heads  of  the  several  metals  in  question  (§§  108 — 113)  must  be 
borne  in  mind.J  (If  notwithstanding,  the  filtrate  is  brownish, 
acidify  it  with  acetic  acid,  boil  and  filter  off  the  small  quantity  of  the 
sulphide  of  nickel  which  then  separates.)  Acidify  the  filtrate  with 
hydrochloric  acid,  evaporate,  filter  off  the  sulphur,  if  necessary,  con- 
tinue the  evaporation  to  dryness,  ignite  the  residue  to  remove  the 
ammonia  salts,  and  determine  the  alkalies  by  the  methods  given  §152. 

B.  Special  Methods. 

1.  Oxide  of  Zinc  from  Potassa  and  Soda,  by  precipitating  53 
the  zinc  from  the  solution  of  the  acetates  with  sulphuretted 
hydrogen  (see  p.  181  and  72)- 

2.  Sesquioxide  of  Iron  from  Potassa  and  Soda,  by  precipita- 
ting the  sesquioxide  of  iron  with  ammonia ; or  by  heating  the 
nitrates  (see  38)- 

* Anna!  d.  Chem.  u.  Pharm.  106,  121.  f Am.  Jour.  Science,  2d  ser.  39,  59. 

% Nickel  and  cobalt  may  be  separated  from  the  alkalies  also  in  the  manner 
given  in  73 


356 


SEPARATION. 


L§  159. 


3.  Protoxide  of  Manganese  from  the  Alkalies. 

a.  Saturate  the  solution  with  chlorine , and  precipitate  the  54 
manganese — as  hydrated  sesquioxide — with  carbonate  of 
baryta  or  ammonia.  The  latter  precipitant  is  apt  to  leave 
some  manganese  in  solution  [see  also  01]. 

b.  Heat  the  nitrates  (Deville)  ; (see  62)- 

II.  Separation  of  the  Oxides  of  the  Fourth  Group  from  the 
Alkaline  Earths. 


§159. 

Index  : — The  Nos.  refer  to  those  in  the  margin. 

Oxide  of  zinc  from  baryta,  strontia,  and  lime,  55,  56,  57,  63. 

“ magnesia,  55,  57. 

Protoxide  of  manganese  from  baryta,  strontia,  and  lime,  55,  56,  59 — 
62—67. 

Protoxide  of  manganese  from  magnesia,  55,  59,  62. 

Protoxides  of  nickel  and  cobalt  from  baryta,  strontia,  and  lime,  55,  56, 63. 

“ magnesia,  55. 

Sesquioxide  of  iron  from  baryta,  strontia,  and  lime,  55,  56,  58. 

“ magnesia,  55,  58. 


A.  General  Method. 

All  Oxides  of  the  Fourth  Group  from  the  Alkaline  Earths. 

Add  to  the  solution  chloride  of  ammonium,  and,  if  acid,  also  am-  55 
monia,  and  precipitate  with  sulphide  of  ammonium,  as  in  52-  Take 
care  to  use  slightly  yellow  sulphide  of  ammonium,  perfectly  satura- 
ted with  sulphuretted  hydrogen,  and  free  from  carbonate  and  sul- 
phate of  ammonia,  and  to  employ  it  in  sufficient  excess.  Insert  the 
cork,  and  let  the  flask  stand  for  some  time,  to  allow  the  precipitate 
to  subside,  then  wash  quickly,  and  as  far  as  practicable,  out  of  the 
contact  of  air,  with  water  to  which  some  sulphide  of  ammonium  has 
been  added.  Acidify  the  filtrate  with  hydrochloric  acid,  heat,  filter 
from  the  sulphur,  and  separate  the  alkaline  earths,  as  directed  in 
§ 154.  If  the  filtrate  is  brownish  from  a little  dissolved  sulphide  of 
nickel,  acidify  it  with  acetic  acid  instead  of  with  hydrochloric  acid, 
boil,  and  filter. 

If  the  quantity  of  the  alkaline  earths  is  rather  considerable,  it  is 
advisable  to  treat  the  slightly  washed  precipitate  once  more  with  hy- 
drochloric acid  (in  presence  of  nickel  or  cobalt,  it  is  not  necessary 
to  effect  complete  solution),  heat  the  solution  gently  for  some  time, 
and  then  reprecipitate  in  the  same  way. 

If  we  have  merely  to  effect  the  removal  of  nickel  and  cobalt,  we 
may  also,  after  .addition  of  sulphide  of  ammonium,  acidify  with  acet- 
ic acid,  and  filter.  Cobalt  alone  may  be  separated  as  follows : after 
precipitating  the  ammoniacal  solution  with  sulphide  of  ammonium, 
boil  the  whole  till  the  free  ammonia  has  escaped,  add  a few  drops  of 
sulphide  of  ammonium  and  ammonia,  and  filter  (H.  Hose*). 


Pogg.  Annal.  110,  416. 


BASES  OF  GROUP  IV. 


357 


§ 159*] 

B.  Special  Methods . 

1.  Baryta,  Strontia,  and  Lime,  from  the  whole  of  the  Oxides 

of  the  Fourth  Group. 

Precipitate  the  baryta  and  strontia  from  the  acid  solution  56 
with  sulphuric  acid  (§§  101  and  102),  in  the  presence  of  lime 
add  ^ — £ volume  of  strong  alcohol  (§  103).  For  baryta  this 
method  is  preferable  to  all  others. 

2.  Oxide  of  Zinc  from  the  Alkaline  Earths. 

Convert  the  bases  into  acetates,  and  precipitate  the  zinc  from  57 
the  solution  as  directed  in  § 108,  1,  b. 

3.  Sesquioxide  of  Iron  from  tile  Alkaline  Earths. 

a.  Mix  the  somewhat  acid  solution  with  enough  chloride  58 
of  ammonium,  heat  to  boiling,  add  slight  excess  of  am- 
monia, boil,  till  the  excess  of  the  latter  is  expelled,  and  fil- 
ter. The  solution  is  free  from  iron,  the  precipitate  is  free 
from  lime,  baryta,  and  strontia,  but  contains  a very  slight 
trace  of  magnesia  (H.  Bose*). 

b.  Precipitate  the  sesquioxide  of  iron  as  basic  acetate  or  for- 
miate  (§  113,  1,  d [and  § 81,  e]  ).  The  method  is  good 
and  can  frequently  be  employed. 

c.  Decompose  the  nitrates  by  heat  (38). 

4.  Protoxide  of  .Manganese  from  the  Alkaline  Earths. 

Separation  of  Manganese  as  Sesquioxide  or  B inoxide. 

a.  Schiel’s  Method.f — Add  to  the  hydrochloric  acid  solution  car-  59 
bonate  of  soda  until  the  fluid  is  nearly  neutralized,  mix  with  acetate 
of  soda,  dilute  sufficiently,  and  then  conduct  chlorine  gas  into  the 
mixture.  The  acetate  of  protoxide  of  manganese  is  decomposed,  and 
the  whole  of  the  manganese  separates  as  binoxide.  The  alkaline 
earths  remain  in  solution.  The  solution  is  kept  heated  to  between 
50°  and  60°,  whilst  the  chlorine  gas  is  transmitted  through  it ; as 
soon  as  the  binoxide  has  separated,  the  transmission  of  the  gas  is 
stopped.  The  protosesquioxide  of  manganese  obtained  by  the  igni- 
tion of  the  binoxide  so  produced  contains  alkali.  The  binoxide  must 
therefore  be  dissolved  in  hydrochloric  acid,  and  the  solution  precipi- 
tated as  directed  § 109,  3.  Instead  of  chlorine  gas,  solution  of  hy- 
pochlorous  acid  or  of  hypochlorite  of  soda  may  be  used.J  In  using 
the  latter,  care  must  be  taken  to  keep  the  fluid  always  slightly  acid 
by  acetic  acid.  The  method  is  good. 

(3.  H.  Bose|]  recommends  to  mix  the  dilute  solution  with  acetate  60 
of  soda,  heat  and  saturate  with  chlorine  gas,  then  to  the  fluid,  which 
becomes  red  from  the  formation  of  permanganic  acid,  to  add  excess 
of  ammonia  (in  presence  of  much  magnesia,  also  chloride  of  ammoni- 


* Pogg.  Annal.  110,  300.  f Sillim.  Journ.  15,  275. 

\ [Bromine  is  the  most  convenient  reagent  to  employ  for  the  above  purpose.  ] 
| Pogg.  Annal.  110,  305. 


358 


SEPARATION. 


[§  160. 


um),  to  boil,  till  all  free  ammonia  is  expelled,  and  filter  off  the  pre- 
cipitated sesquioxide  of  manganese.  The  manganese  may  also  be 
completely  precipitated  from  a dilute  cold  fluid  saturated  with  chlo- 
rine by  means  of  carbonate  of  baryta. 

[7.  Reichardt*  directs  to  add  to  the  hot  and  dilute  hydrochlor-  61 
ic  acid  solution  carbonate  of  soda  until  a slight  permanent  precipi- 
tate is  formed,  to  redissolve  this  by  the  least  necessary  hydrochloric 
acid,  and  to  add  excess  of  (crystals  of)  acetate  of  soda.  The  acetic 
solution  thus  obtained  is  heated  just  to  boiling,  and  solution  of  hypo- 
chlorite of  soda  (procured  by  boiling  good  bleaching  powder  with 
solution  of  carbonate  of  soda,  using  the  latter  in  but  slight  excess)  is 
added  in  sufficient  quantity  with  stirring.  That  enough  hypochlo- 
rite has  been  added  is  shown  by  the  reddening  and  subsequent  bleach- 
ing of  litmus  paper.  This  test  should  not  be  applied  until  the  hy- 
pochlorite has  had  a little  time  to  react  on  the  manganese.  If  the 
acetic  acid  should  be  neutralized  more  must  be  added.  After  a few 
minutes  filter  and  wash  with  hot  water.  Reichardt  assures  that  the 
bin  oxide  thus  obtained  is  free  from  alkali.] 

0.  Deville’s  Method.f — The  bases  must  be  present  as  nitrates.  62 
Heat  in  a covered  platinum  dish  to  from  200°  to  250°,  until  the 
formation  of  fumes  has  completely  ceased,  and  the  mass  has  become 
black;  and  proceed  in  all  other  respects  as  directed  in  38*  The 
presence  of  a small  quantity  of  organic  matter,  or  the  action  of  a too 
intense  heat,  may  cause  the  reduction  of  traces  of  binoxide  of  man- 
ganese, and  their  solution  in  nitrate  of  ammonia ; these  traces  will  be 
found  with  the  magnesia. 

5.  Protoxide  of  Cobalt,  Protoxide  of  Nickel,  and  Oxide  of 
Zinc,  from  Baryta,  Strontia,  and  Lime. 

Mix  with  carbonate  of  soda  in  excess,  add  cyanide  of  potassium,  63 
heat  very  gently,  until  the  precipitated  carbonates  of  protoxide  of 
cobalt,  protoxide  of  nickel,  and  oxide  of  zinc  are  redissolved ; then 
filter  the  alkaline  earthy  carbonates  from  the  solution  of  the  cyanides 
in  cyanide  of  potassium.  The  former  are  dissolved  in  dilute  hydro- 
chloric acid,  and  separated  according  to  § 154;  the  latter  are  sepa- 
rated according  to  § 160. 

III.  Separation  of  the  Oxides  of  the  Fourth  Group  from 

THOSE  OF  THE  THIRD,  AND  FROM  EACH  OTHER. 

§160. 

Index : — The  Nos.  refer  to  those  in  the  margin. 

Alumina  from  oxide  of  zinc,  64,  65,  70,  71,  81. 

“ protoxide  of  manganese,  64,  65,  66,  68,  70,  71,  78. 

“ protoxides  of  nickel  and  cobalt,  64,  65,  67,  70,  71,  81. 

“ protoxide  of  iron,  64.  65,  66,  67. 

“ sesquioxide  of  iron,  65,  66,  67,  75,  84. 

Sesquioxide  of  chromium  from  oxide  of  zinc,  protoxides  of  manganese,  nickel, 

cobalt,  and  iron,  64.  65,  76. 

“ sesquioxide  of  iron,  65,  75,  76. 

Analysis  of  chromic  iron,  77. 


* Fres.  Zeitschrift,  v.  62. 


\ Joum.  f.  prakt.  Chem.  60,  11 


§ 160.] 


BASES  OF  GROUP  IY. 


359 


I 


Oxide  of  zinc  from  alumina,  64,  65,  70,  71,  81. 

“ protoxide  of  manganese,  64,  65,  76,  78. 

protoxide  of  nickel,  74,  83. 
u protoxide  of  cobalt,  72,  74,  79. 

u sesquioxide  of  iron,  64,  69,  70,  71,  85. 

Protoxide  of  manganese  from  alumina,  64,  65,  66,  68,  70,  71,  78. 

sesquioxide  of  chromium,  64,  65,  76. 
“ oxide  of  zinc,  78. 

“ protoxide  of  nickel,  73,  74,  78,  80. 

“ protoxide  of  cobalt,  73,  74,  79,  80. 

“ sesquioxide  of  iron,  64,  68,  69,  70,  71. 

Protoxide  of  nickel  from  alumina,  64,  65,  67,  70,  71,  81. 

“ sesquioxide  of  chromium,  64,  65,  76. 

u oxide  of  zinc,  72,  74,  83. 

“ protoxide  of  manganese,  73,  74,  78,  80. 

“ protoxide  of  cobalt,  79,  82. 

“ sesquioxide  of  iron,  64,  69,  70,  71,  73,  85. 

Protoxide  of  cobalt  from  alumina,  64,  65,  67,  70,  71,  81. 

“ sesquioxide  of  chromium,  64,  65,  76. 

“ oxide  of  zinc,  72,  74,  79. 

“ protoxide  of  manganese,  73,  74,  79,  80. 

“ protoxide  of  nickel,  79,  82. 

u sesquioxide  of  iron,  64,  69,  70,  71,  73. 

Protoxide  of  iron  from  alumina,  64,  65,  66,  67. 

“ sesquioxide  of  chromium,  64,  65,  76. 

11  sesquioxide  of  iron,  64,  85. 

Sesquioxide  of  iron  from  alumina,  66,  67,  75,  84. 

“ sesquioxide  of  chromium,  65,  75,  76. 

“ oxide  of  zinc,  64,  69,  70,  71,  85. 

“ protoxide  of  manganese,  64,  68,  69,  70,  71. 

“ protoxide  of  nickel,  64,  69,  70,  71,  73,  85. 

u protoxide  of  cobalt,  64,  69,  70,  71,  73. 

“ protoxide  of  iron,  64,  85. 


A.  General  Methods. 

1.  Precipitation  of  some  Oxides  by  Carbonate  of  Paryta. 

Sesquioxide  of  Iron,  Alumina,  and  Sesquioxide  of  Chromium, 

FROM  ALL  OTHER  BASES  OF  THE  FOURTH  GROUP. 

Mix  the  sufficiently  dilute  solution  of  the  chlorides  or  nitrates,  04 
but  not  sulphates,  which  must  contain  a little  free  acid,*  in  a flask, 
with  a moderate  excess  of  carbonate  of  baryta  diffused  in  water ; 
cork,  and  allow  to  stand  some  time  in  the  cold,  with  occasional 
shaking.  The  sesquioxide  of  iron,  alumina,  and  sesquioxide  of  chro- 
mium, are  completely  separated,!  whilst  the  other  bases  remain  in 
solution,  with  the  exception  perhaps  of  traces  of  protoxide  of  cobalt 
and  protoxide  of  nickel,  which  will  generally  fall  down  with  the  preci- 
pitated oxides.  This  may  be  prevented, # at  least  as  regards  nickel,  by 
addition  of  chloride  of  ammonium  to  the  fluid  to  be  precipitated 
(Schwarzenberg  J).  Decant,  stir  up  with  cold  water,  allow  to  deposit, 
decant  again,  filter,  and  wash  with  cold  water.  The  precipitate  con- 


* If  there  is  much  free  acid,  the  greater  part  of  it  must  first  be  saturated 
with  carbonate  of  soda. 

f The  separation  of  the  sesquioxide  of  chromium  requires  the  most  time. 

\ Annal.  d.  Chem.  u.  Pharm.  97,  216. 


360 


SEPARATION. 


L§  ieo. 


tains,  besides  tbe  precipitated  oxides,  carbonate  of  baryta ; and  the 
filtrate,  besides  the  non-precipitated  oxides,  a salt  of  baryta. 

If  protoxide  of  iron  is  present, 
c and  it  is  wished  to  separate  it  by 

this  method  from  sesquioxide  of 
iron,  &e.,  the  air  must  be  excluded 
during  the  whole  of  the  operation. 

In  that  case,  the  solution  of  the 
substance,  the  precipitation,  and  the 
washing  by  decantation,  are  effected 
in  a flask  (A,  fig.  66),  through 
which  carbonic  acid  is  transmitted 
(e?).  The  washing  water,  boiled  free 
from  air,  and  cooled  out  of  contact 
of  air  (preferably  in  a current  of 
carbonic  acid),  is  poured  in  through 
a funnel  tube  (c),  and  the  fluid 
drawn  off  by  means  of  a movable 
syphon  (6)  ; all  the  tubes  are  fitted 
air-tight  into  the  cork;  they  are 
smeared  with  tallow. 

2.  Precipitation  of  the  Oxides  of  the  Fourth  Group , by 
Sulphide  of  Sodium , or  Sulphide  of  Ammonium , from 
Alkaline  Solution  effected  with  the  aid  of  Tartaric  Acid. 

Alumina  and  Sesquioxide  of  Chromium  from  the  Oxides  of 
the  Fourth  . Group. 

Mix  the  solution  with  tartaric  acid,  then  with  pure  solution  of  05 
soda  or  potassa  until  the  fluid  has  cleared  again  ; * add  sulphide  of 
sodium  as  long  as  a precipitate  forms,  allow  it  to  deposit  until  the 
supernatant  fluid  no  longer  exhibits  a greenish  or  brownish  tint ; 
decant,  stir  the  precipitate  up  with  water  containing  sulphide  of  so- 
dium, decant  again,  transfer  the  precipitate,  which  contains  all  the 
metals  of  the  fourth  group,  to  a filter,  wash  with  water  containing 
sulphide  of  sodium,  and  separate  the  metals  as  directed  in  B.  Add 
to  the  filtrate  nitrate  of  potassa,  and  evaporate  to  dryness  ; fuse  the 
residue,  and  separate  the  alumina  from  the  chromic  acid  formed,  as 
directed  § 157.  If  you  have  merely  to  separate  alumina  from  the 
oxides  of  the  fourth  group,  it  is  better,  after  addition  of  tartaric  acid, 
to  supersaturate  with  ammonia,  add  chloride  of  ammonium,  and  pre- 
cipitate in  a flask  with  sulphide  of  ammonium.  When  the  precipi- 
tate has  settled  it  is  filtered  off  and  washed  with  water  containing 
sulphide  of  ammonium.  The  filtrate  is  evaporated  with  addition  of 
carbonate  of  soda  and  nitrate  of  potassa  to  dryness,  fused,  and  the 
alumina  determined  in  the  residue. 


* Sesquioxide  of  chromium  and  oxide  of  zinc  cannot  be  obtained  together  in 
alkaline  solution  (Chancel,  Compt.  rend.  43,  927 ; Journ.  f.  prakt.  Cbem.  70. 
378). 


§ 160.] 


BASES  OF  GROUP  IV. 


361 


B.  Special  Methods. 

1.  Solubility  of  Alumina  in  Caustic  Alkalies. 

a.  Alumina  from  Protoxide  and  Sesquioxide  of  Iron,  and 
Small  Quantities  of  Protoxide  of  Manganese  (but  not  from  the 
protoxides  of  nickel  and  cobalt). 

Heat  the  rather  concentrated  acid  solution  in  a flask  to  boiling,  66 
remove  from  the  gas,  and  reduce  the  sesquioxide  of  iron  present  by 
sulphite  of  soda.  Replace  the  fluid  over  the  lamp,  keep  boiling  some 
time,  and  then  neutralize  with  carbonate  of  soda,  add  solution  of  pure 
soda  or  potassa  in  excess,  and  boil  for  some  time. 

If  the  analyzed  substance  contains  much  iron,  the  precipitate  will 
become  black  and  granular,  which  is  a proof  that  the  iron  has  been 
converted  into  protosesquioxide.  The  tendency  to  bumping,  preced- 
ing the  actual  ebullition  of  the  fluid,  may  be  guarded  against  by 
means  of  a spiral  coil  of  platinum  wire  placed  in  the  liquid,  or  by 
constant  agitation  of  the  latter  : when  ebullition  has  once  set  in,  there 
is  no  further  need  of  these  precautions.  Remove  the  fluid  now  from 
the  gas,  allow  to  deposit,  pass  the  clear  fluid  through  a Alter,  which 
must  not  be  over-porous,  boil  the  precipitate  again  with  a fresh  quan- 
tity of  solution  of  soda,  then  wash  it,  Arst  by  decantation,  afterwards 
on  the  Alter  with  hot  water.  Acidify  the  alkaline  Altrate  with  hy- 
drochloric acid,  boil  with  some  chlorate  of  potassa  (to  destroy  any 
traces  of  organic  matter),  concentrate  by  evaporation,  and  precipi- 
tate the  alumina  as  directed  § 105,  a*  The  boiling  of  the  precipi- 
tated oxides  with  the  solution  of  soda  is  effected  best  in  a somewhat 
capacious  silver  or  platinum  dish.  A solution  of  soda  containing 
alumina  and  silica  must  be  particularly  avoided. 

If  sesquioxide  of  chromium  was  present  in  the  analyzed  sub- 
stance, you  will  And  the  principal  portion  of  it  with  the  sesquioxide 
of  iron ; but  a small  quantity  has  been  oxidized  to  chromic  acid,  and 
is  accordingly  found  in  the  fluid  Altered  from  the  alumina. 

b.  The  method  described  in  a is  often  employed  also  in  a modiAed 
form,  omitting  the  reduction  of  the  sesquioxide  of  iron ; in  which 
case  the  process  is  performed  as  follows  : — Precipitate  with  ammonia, 
decant,  Alter,  wash,  transfer  the  precipitate  still  moist  to  a platinum 
dish,  without  the  aid  of  water,  and  remove  the  last  particles  adhering 
to  the  Alter  by  means  of  warm  hydrochloric  acid,  which  is  allowed 
to  drop  into  the  platinum  dish.  The  aqueous  washings  of  the  Alter 
are  kept  separate.  When  the  precipitate  in  the  platinum  dish  has 
dissolved,  add,  very  cautiously,  concentrated  solution  of  caustic 
potassa,  or  carbonate  of  soda,  until  the  free  acid  is  almost  neutralized, 
and  apply  heat,  Anally  to  boiling ; after  this,  remove  the  lamp,  and 
add  a lump  of  pure  hydrate  of  potassa  sufficiently  large  to  redissolve 
the  precipitated  alumina,  leaving  the  hydrated  sesquioxide  of  iron 
undissolved.  Rinse  the  platinum  dish  now  into  the  beaker  which 
contains  the  washings  of  the  Alter;  wash  the  sesquioxide  of  iron, 
Arst  by  decantation,  then  upon  the  Alter  with  boiling  water,  and  treat 
the  Altrate  as  in  a. 

If  the  fluid  in  which  it  is  intended  to  separate  sesquioxide  of  iron 
and  alumina  contains  lime  or  magnesia,  some  alumina  is  likely  to 
remain  undissolved. 


Joum.  f.  prakt.  Chem.  45,  261. 


362 


SEPARATION. 


c.  Alumina  from  Sesquioxide  of  Iron  and  Protoxides  of  Iron, 
Cobalt,  and  Nickel. 

Fuse  the  oxides  with  hydrate  of  potassa  in  a silver  crucible,  boil  67 
the  mass  with  water,  and  filter  the  alkaline  fluid,  which  contains  the 
alumina,  f*’om  the  oxides,  which  are  free  from  alumina,  but  contain 
potassa  (H.  Rose). 

2.  Different  behavior  of  the  Oxides  towards  Ammonia  in  the 

presence  of  Chloride  of  Ammonium. 

Alumina  and  Sesquioxide  of  Iron  from  Protoxide  of  Man- 
ganese. 

The  solution  should  be  sufficiently  dilute,  mixed  with  chloride  of  68 
ammonium,  and  slightly  acid.  Heat  to  boiling,  add  ammonia  in 
moderate  excess,  and  allow  to  boil  gently  without  interruption  till  all 
free  ammonia  is  expelled,  then  filter  off  the  precipitate  which  con- 
tains the  sesquioxide  of  iron  and  the  alumina  from  the  fluid  contain- 
ing the  manganese.  If  the  quantity  of  the  manganese  is  small,  the 
precipitate  will  contain  merely  unweighable  traces  of  it.  If,  on  the 
other  hand,  much  is  present,  the  precipitate  after  being  partially 
washed  is  redissolved  in  hydrochloric  acid,  and  the  above  precipita- 
tion is  repeated.  Results  good  (H.  Rose*). 

3.  Different  deportment  of  neutralized  Solutions  at  boiling  heat. 

Sesquioxide  of  Iron  from  Protoxides  of  Manganese,  Nickel 
and  Cobalt,  Oxide  of  Zinc,  and  other  strong  Bases. 

Mix  the  dilute  solution  largely  with  chloride  of  ammonium  (at  least  69 
20  of  NH4C1  to  1 of  oxide),  add  carbonate  of  ammonia  in  small 
quantities,  at  last  drop  by  drop  and  in  very  dilute  solution,  as  long 
as  the  precipitated  iron  redissolves,  which  takes  place  promptly  at  first, 
but  more  slowly  towards  the  end.  As  soon  as  the  fluid  has  lost  its 
transparency,  without  showing,  however,  the  least  trace  of  a distinct 
precipitate  in  it,  and  fails  to  recover  its  clearness  after  standing  some 
time  in  the  cold,  but,  on  the  contrary,  becomes  rather  more  turbid 
than  otherwise,  the  reaction  may  be  considered  completed.  When 
this  point  has  been  attained,  heat  slowly  to  boiling,  and  keep  in 
ebullition  for  a short  time  after  the  carbonic  acid  has  been  entirely 
expelled.  The  sesquioxide  of  iron  separates  as  a basic  salt,  which 
rapidly  settles,  if  the  solution  was  not  too  concentrated.  Add  now 
a drop  of  ammonia,  to  see  whether  the  iron  has  been  completely 
thrown  down,  then  a little  more  ammonia,  to  convert  the  basic  salt 
of  iron,  which  has  a tendency  to  dissolve  upon  cooling,  into  hydrated 
sesquioxide,  and  filter.  To  insure  accurate  results,  the  fluid  must 
not  contain  more  than  3*4  grm.  sesquioxide  of  iron  in  the  litre,  and 
must  be  tolerably  free  from  sulphuric  acid,  since  it  is  difficult  in 
presence  of  the  latter  to  hit  the  exact  point  of  saturation.  (Herschel,! 
Schwarzenberg.J)  The  precipitate  should  be  washed  with  water 
containing  chloride  of  ammonium. 


* Pogg.  Annal.  110,  304  u.  307.  f Anna!  de  Chim.  et  de  Phys.  49,  306. 
\ Annal.  d.  Chem.  u.  Pharm.  97,  216. 


160.] 


BASES  OF  GROUP  IV. 


363 


4.  Method  based  on  the  behavior  of  the  Acetates  at  a boiling  heat. 

Sesquioxide  of  Iron  and  Alumina  from  Protoxide  of  Manga- 
nese, Oxide  of  Zinc,  Protoxide  of  Cobalt,  and  (but  not  so  well) 
Protoxide  of  Nickel. 

' Precipitate  the  sesquioxide  of  iron  and  alumina  according  to  § 113,  70 
1,  d.  See  also  § 81,  e.  The  precipitate  is  free  from  manganese,  co- 
balt, and  zinc  ; but  it  contains  some  nickel,  from  which  it  can  only 
be  freed  by  redissolving  (after  slight  washing),  reprecipitating  in  the 
same  manner,  and  repeating  the  operation  a third  time.  The  method 
is  more  suited  to  the  separation  of  sesquioxide  of  iron,  or  of  sesqui- 
oxide of  iron  and  alumina,  than  of  alumina  alone.  Results  good. 

5.  Method  based  on  the  different  behavior  of  the  Succinates. 

Sesquioxide  of  Iron  (and  Alumina)  from  Oxide  of  Zinc,  and 

Protoxides  of  Manganese,  Nickel,  and  Cobalt. 

The  solution  should  contain  no  considerable  quantity  of  sulphuric  71 
acid.  If  acid,  as  is  usually  the  case,  add  ammonia  till  the  color  is 
reddish  brown,  then  acetate  of  soda,  or  of  ammonia  (H.  Rose)  till 
the  color  is  deep  red,  finally  precipitate  with  neutral  alkaline  succi- 
nate at  a gentle  heat,  and  filter  the  succinate  of  sesquioxide  of  iron 
from  the  solution  which  contains  the  rest  of  the  metals.  For  the 
further  treatment  of  the  precipitate,  see  § 113,  1,  c.  With  proper 
care  the  separation  is  complete,  and  especially  to  be  recommended 
when  a relatively  large  quantity  of  iron  is  present.  The  method  may 
also  be  used  in  the  presence  of  alumina.  The  latter  falls  down  com- 
pletely with  the  iron.  (E.  Mitsclierlich,  Pagels*.) 

6.  Different  deportment  of  several  Sulphides  with  Acids , or  of 

the  Acetic  Acid  Solutions  with  Sulphuretted  Hydrogen. 

[a.  Oxide  of  Zinc  from  Protoxides  of  Nickel  and  Cobalt. 
Brunner’s  Method.! 

The  metals  must  exist  in  dilute  nitric  or  hydrochloric  solution  (not  7 2 
more  than  1 grm.  of  both  oxides  in  ^ litre).  This  is  so  nearly  neu- 
tralized by  carbonate  of  soda  that  only  a very  small  quantity  of  free 
acid  remains.  To  accomplish  this  purpose  it  is  best  to  add  a dilute 
solution  of  carbonate  until  a slight  precipitate  is  left,  after  agitating 
and  standing  for  some  time,  and  then  to  remove  this  by  one  or  more 
drops  of  dilute  acid.  Conduct  into  the  liquid  thus  prepared  hydro- 
sulphuric  acid,  which,  after  a time,  produces  a perfectly  white  pre- 
cipitate of  sulphide  of  zinc.  After  a good  share  of  the  zinc  has  thus 
been  thrown  down,  add  to  the  liquid  a few  drops  of  a very  dilute 
solution  of  acetate  of  soda  and  continue  the  passage  of  hydrosulphuric 
acid  gas  as  long  as  the  precipitate  appears  to  increase,  and  afterwards 
let  the  whole  stand  12  hours  at  ordinary  temperatures.  The  preci- 
pitate settles  perfectly  and  washes  easily  upon  the  filter. 

In  order  to  make  certain  of  the  thorough  separation  of  the  zinc, 
add  to  a portion  of  the  filtered  liquid  a drop  of  solution  of  acetate  of 
soda  and  treat  again  with  hydrosulphuric  acid  gas.  If  a white  tur- 
bidity ensues  the  whole  filtrate  must  be  subjected  to  the  same  opera- 
tion. 


* Jahresber.  v.  Kopp  u.  Will.  1858,  617.  f Dmgler’s  polyt.  Joum.  150,  370. 


364 


SEPARATION. 


The  sulphide  of  zinc  is  farther  treated  according  to  § 108,  2. 

This  separation  succeeds  only  <when  the  directions  are  strictly  ad- 
hered to.  If  the  solution  be  neutral,  or  contain  too  much  acetate  o‘f 
soda,  or  be  heated,  nickel  will  go  down  with  the  zinc.  If  iron  be 
present  it  must  be  previously  separated.  Mixter  has  employed  this 
method  in  the  analysis  of  German  silver  with  most  satisfactory  re- 
sults.] 

b.  Protoxides  of  Cobalt  and  Nickel  from  Protoxide  of  Man- 
ganese and  the  Oxides  of  Iron. 

The  solution,  which  must  be  free  from  nitric  acid,  is,  after  neutra-  73 
lization  of  any  free  acid  which  may  be  present  by  ammonia,  precipi- 
tated with  sulphide  of  ammonium,  and  highly  dilute  hydrochloric 
acid,  or — if  manganese  alone  has  to  be  separated — acetic  acid  then 
added,  and  sulphuretted  hydrogen  gas  conducted  into  the  fluid  to 
saturation,  with  frequent  stirring.  This  serves  to  dissolve  the  sul- 
phide of  manganese  and  the  sulphide  of  iron,  whilst  the  sulphide  of 
cobalt  and  the  sulphide  of  nickel,  though  the  latter  less  completely, 
remain  undissolved.  The  filtrate  is  reprecipitated  by  addition  of 
ammonia  and  sulphide  of  ammonium,  and  the  above  treatment  is  re- 
peated. The  results  are  accurate.  It  is  advisable,  however,  to  test 
the  weighed  cobalt  and  nickel  compounds,  for  manganese  and  iron. 

c.  Protoxides  of  Cobalt  and  Nickel  from  Protoxide  of  Man- 
ganese and  Oxide  of  Zincl 

a.  Put  the  weighed  mixture  of  the  oxides  in  a porcelain  or  plati-  74 
num  boat,  insert  this  into  a tube,  heat  to  dull  redness,  whilst  con- 
ducting sulphuretted  hydrogen  gas  over  it.  Let  the  sulphides  formed 
cool  in  the  current  of  gas,  and  then  digest  them  for  several  hours 
with  cold  dilute  hydrochloric  acid,  which  dissolves  only  the  sulphide 
of  manganese  (and  sulphide  of  zinc).  The  sulphides  of  nickel  and 
cobalt  are  left  behind  pure  (Ebelmen*). 

/?.  Precipitate  with  carbonate  of  soda,  filter,  wash,  and  ignite  ; 
mix  1 part  of  the  residue  with  1*5  of  sulphur  and  0*75  of  carbonate 
of  soda,  and  heat  the  mixture  in  a small  retort  as  strongly  as  possi- 
ble for  half  an  hour.  Allow  the  mixture  to  cool,  and  extract  the 
sulphide  of  zinc  (and  sulphide  of  manganese)  formed,  with  dilute 
hydrochloric  acid  (1  part  acid  to  10  water),  BRUNNER.f 

7.  Different  deportment  of  the  several  Oxides  with  Hydrogen 
Gas  at  a red  heat. 

Sesquioxide  of  Iron  from  Alumina  and  Sesquioxide  of  Chro- 
mium. 

[Precipitate  with  ammonia,  heat,  filter,  ignite  and  weigh.  Tritu-  75 
rate,  and  weigh  off  a portion  in  a platinum  crucible.  Ignite  to  red- 
ness in  a stream  of  hydrogen  gas  as  long  as  water  forms  (about  1 


* Anna!  d.  Chem.  u.  Pharm.  72,  329.  Ebelmen  has  given  his  method  simply 
for  the  separation  of  cobalt  and  nickel  from  manganese. 

f Annal.  d.  Chem.  u.  Pharm.  80,  364.  Brunner  has  given  his  method  simply 
for  nickel  and  zinc. 


§ 160.] 


BASES  OF  GROUP  IV. 


365 


hour).  Then  ignite  over  the  blast-lamp  in  a current  of  mixed 
hydrogen  and  hydrochloric  acid  gases. 

This  leaves  the  alumina  and  sesquioxide  of  chromium  in  a state  of 
purity ; the  iron  volatilizes  as  protochloride,  and  is  determined  by  the 
loss.  (Method  of  Rivot  and  Deville  modified.)] 

8.  Different  capacity  of  the  several  Oxides  to  be  converted  into 
higher  Oxides , or  higher  Chlorides. 

a.  Sesquioxide  of  Chromium  from  all  the  Oxides  of  the 
Fourth  Group. 

Fuse  the  oxides  with  nitrate  of  potassa  and  carbonate  of  soda  7 0 
(comp.  § 157),  boil  the  mass  with  water,  add  a sufficient  quantity  of 
spirit  of  wine,  and  heat  gently  for  several  hours.  Filter,  and  deter- 
mine in  the  filtrate  the  chromium  as  directed  § 130,  and  in  the  residue 
the  bases  of  the  fourth  group.  The  following  is  the  theory  of  this 
process : the  oxides  of  zinc,  cobalt,  nickel,  iron,  and  partly  that  of 
manganese,  separate  upon  the  fusion,  whilst,  on  the  other  hand,  man- 
ganate  (perhaps  also  some  ferrate)  and  chromate  of  potassa  are  formed. 
Upon  boiling  with  water,  part  of  the  manganic  acid  of  the  manga- 
nate  of  potassa  is  converted  into  permanganic  acid  at  the  expense  of 
the  oxygen  of  another  part,  which  is  reduced  to  the  state  of  binoxide ; 
the  latter  separates,  whilst  the  potassa  salts  are  dissolved.  The  addi- 
tion of  alcohol,  with  the  application  of  a gentle  heat,  effects  the  decom- 
position of  the  manganate  and  permanganate  of  potassa,  binoxide 
of  manganese  being  separated.  Upon  filtering  the  mixture,  we  have 
therefore  now  the  whole  of  the  chromium  in  the  filtrate  as  alkaline 
chromate,  and  all  the  oxides  of  the  fourth  group  on  the  filter.  Alu- 
mina, if  present,  will  be  found  partly  in  the  residue,  partly  as  alka- 
line aluminate  in  the  filtrate ; proceed  with  the  latter  according  to  49. 

If'  you  have  to  deal  with  the  native  compound  of  sesquioxide  of 
chromium  with  protoxide  of  iron  (chromic  iron)  the  above  method 
does  not  answer.  In  this  case  the  following  plan  may  be  adopted : 

Take  0*5  grm.  of  the  impalpable  powder,  and  fuse  in  a capacious  77 
platinum  crucible  with  6 grm.  bisulphate  of  potassa  for  fifteen 
minutes,  at  a temperature  scarcely  above  the  fusing  point  of  the 
latter,  then  raise  the  heat  somewhat,  so  that  the  bottom  of  the  cru- 
cible may  just  appear  red,  and  keep  it  so  for  fifteen  or  twenty  minutes. 

The  fusing  mass  should  not  rise  higher  than  halfway  up  the  crucible. 

The  mass  begins  to  fuse  quietly,  and  abundant  fumes  of  sulphuric 
acid  escape.  At  the  expiration  of  twenty  minutes  the  heat  is  in- 
creased as  much  as  necessary  to  drive  out  the  second  equivalent  of 
sulphuric  acid,  and  even  to  decompose  partially  the  sulphate  of  iron 
and  chromium.  To  the  fused  mass  now  add  3 grm.  pure  carbonate 
of  soda,  heat  to  fusion,  and  add  in  small  portions  from  time  to  time 
during  an  hour  3 grm.  nitre,  maintaining  a gentle  red  heat  all  the 
while,  then  heat  for  15  minutes  to  bright  redness.  Treat  the  cold 
mass  with  boiling  water,  filter  hot,  wash  the  residue  with  hot  water, 
then  digest  in  the  heat  with  hydrochloric  acid.  If  anything  remains 
undissolved,  it  is  a portion  of  the  ore  undecomposed,  and  must  be 
subjected  again  to  the  above  operation.  To  weigh  such  a residue 
and  deduct  it  from  the  ore  first  taken  is  not  good,  as  it  never  pos- 


366 


SEPARATION. 


[§  160. 


sesses  the  composition  of  the  original  substance.  The  alkaline  solu- 
tion. which  often  contains,  besides  the  chromic  acid,  also  some  silicic, 
titanic,  and  manganic  acids  and  alumina,  is  evaporated  with  excess 
of  nitrate  of  ammonia  on  a water-bath  nearly  to  dryness,  and  till  all 
free  ammonia  is  expelled.  On  addition  of  water,  the  silicic  acid, 
alumina,  titanic  acid,  and  sesquioxide  of  manganese  remain  undis- 
solved, while  the  chromic  acid  passes  into  solution,  and  is  to  be  de- 
termined according  to  § 130.  (T.  S.  Hunt.  F.  A.  Genth*.) 


b.  Protoxide  of  Manganese  from  Alumina,  Protoxide  of 
Nickel,  and  Oxide  of  Zinc  (but  not  from  protoxide  of  cobalt  and 
the  oxides  of  iron). 

After  ScHiEL.f — Conduct  chlorine  gas  into  the  solution  mixed  78 
with  acetate  of  soda  (see  59,  60  and  61). 


9.  Method  based  upon  the  different  deportment  of  the  Nitrites. 

Protoxide  of  Cobalt  from  Protoxide  of  Nickel,  also  from 
Protoxide  of  Manganese  and  Oxide  of  Zinc. 

The  separation  of  cobalt  as  nitrite  of  sesquioxide  of  cobalt  and  79 
potassa,  which  was  recommended  first  by  Fischer,  J afterwards  by  A. 
Stromeyer||  is  unquestionably  the  best  method  for  separating  cobalt 
and  nickel.  The  best  mode  of  proceeding  is  as  follows : — The  solu- 
tion of  the  oxides  (from  which  any  iron  [as  well  as  all  alkaline  earths 
where  nickel  is  present,]  must  first  be  separated)  is  evaporated  to  a 
small  bulk,  and  then,  if  much  free  acid  is  present,  neutralized  with 
potassa.  Then  add  a concentrated  solution  of  nitrite  of  potassa 
(previously  neutralized  with  acetic  acid  and  filtered  from  any  flocks 
of  silica  and  alumina  that  may  have  separated)  in  sufficient  quantity 
and  finally  acetic  acid,  till  any  flocculent  precipitate  that  may  have 
formed  from  excess  of  potassa  has  redissolved  and  the  fluid  is  decid- 
edly acid.  Allow  it  to  stand  at  least  for  24  hours  in  a warm  place, 
take  out  a portion  of  the  supernatant  fluid  with  a pipette,  mix  it 
with  more  nitrite  of  potassa  and  observe  whether  a further  precipi- 
tation takes  place  in  this  after  long  standing.  If  no  precipitate  is 
formed  the  whole  of  the  cobalt  has  fallen  down,  otherwise  the  small 
portion  must  be  returned  to  the  principal  solution,  some  more  nitrite 
of  potassa  added,  and  after  long  standing  the  same  test  applied. 
Thus  alone  can  the  analyst  be  sure  of  the  complete  precipitation  of  the 
cobalt.  Finally  filter  and  treat  the  precipitate  according  to  § 111,  4, 
if  you  desire  to  determine  it  after  the  method  of  Genth  and  Gibbs. 

H.  Rose  recommends  washing  the  precipitate  with  a saturated  so- 
lution of  chloride  of  potassium  or  of  sulphate  of  potassa,  then  dis- 
solving it  in  hydrochloric  acid,  precipitating  the  protoxide  of  cobalt 
from  the  solution  with  potassa,  washing,  igniting  in  hydrogen,  wash- 
ing the  metal  and  finally  weighing. 


* Zeitschrift  f.  analyt.  Chem.  1.  498. 

f Sillim.  Joum.  15,  275.  Schiel  speaks  only  of  the  separation  of  manganese 
from  iron  (?)  and  nickel ; but  it  is  obvious  that  its  separation  from  alumina  and 
zinc  may  be  effected  by  the  same  method. 

^ Pogg.  Annal.  72,  477.  ||  Annal.  d.  Chem.  u.  Pharm.  96,  218. 


160.] 


BASES  OF  GROUP  IV. 


367 


10.  Method  based  on  the  different  behavior  of  the  Phosphates. 

Manganese  from  Nickel  and  Cobalt. 

Mix  the  warm  solution  of  the  sulphates  or  chlorides  with  chloride  of  80 
ammonium  and  ammonia,  then  with  phosphoric  acid  (the  ammonia 
must  remain  still  in  large  excess).  The  white  precipitate  is  2 Mn  O, 

N H4  O,  P 05-f-  2 H O (which  on  ignition  becomes  2 Mn  O,  P 05),  the 
' filtrate  contains  the  whole  of  the  nickel.  If  cobalt  is  present  the  preci- 
pitate must  be  dissolved  in  hydrochloric  acid  and  reprecipitated  with 
ammonia,  in  order  to  free  it  from  the  small  quantity  of  cobalt  which 
first  falls  down  with  it.  The  precipitate  becomes  crystalline  soon 
after  falling,  it  is  to  be  washed  with  solution  of  chloride  of  ammo- 
nium containing  free  ammonia  (T.  H.  Henry*).  [See  also  § 109,  3.] 

The  test-analyses  are  satisfactory. 

11.  Methods  based  upon  the  different  deportment  with  Cyanide 

of  Potassium. 

a.  Alumina  from  Oxide  of  Zinc,  Protoxide  of  Cobalt,  and 
Protoxide  of  Nickel. 

Mix  the  solution  with  carbonate  of  soda,  add  cyanide  of  potassium  81 
in  sufficient  quantity,  and  digest  in  the  cold,  until  the  precipitated 
carbonates  of  zinc,  cobalt  and  nickel  are  redissolved.  Filter  off  the 
undissolved  alumina,  wash,  and  remove  the  alkali  which  it  contains, 
by  resolution  in  hydrochloric  acid  and  reprecipitation  by  ammonia 
(Fresenius  and  HaidlenI). 

b.  Protoxide  of  Nickel  from  Protoxide  of  Cobalt. 

Liebig’s  Method. J — Mix  the  solution  of  the  two  oxides,  which  82 

must  be  free  from  other  oxides,  with  hydrocyanic  acid,  then  with  so- 
lution of  potassa,  and  warm,  until  everything  is  dissolved.  (Cyanide 
of  potassium,  free  from  cyanate,  may  be  used  instead  of  hydro- 
cyanic acid  and  potassa.)  The  solution  looks  reddish-yellow  ; heat  to 
boiling  to  remove  the  free  hydrocyanic  acid.  By  this  process  the 
double  cyanide  of  cobalt  and  potassium  (K  Cy,  Co  Cy)  in  the  solu- 
tion is  mostly  converted,  with  evolution  of  hydrogen,  into  cobalti- 
cyanide  of  potassium  (K3  Co2  Cy6)j|  whilst  the  double  cyanide  of 
nickel  and  potassium  in  the  solution  remains  unaltered.  Let  the 
solution  cool,  then  supersaturate  with  chlorine,  and  constantly  redis- 
solve the  precipitate  of  cyanide  of  nickel  which  forms,  by  addition 
of  solution  of  soda  or  potassa.  The  chlorine  does  not  act  upon  the 
cobalticyanide  of  potassium,  but  it  decomposes  the  double  cyanide 
of  nickel  and  potassium,  and  throws  down  the  whole  of  the  nickel 
as  black  peroxide.  [This  must  be  washed,  dissolved,  and  reprecipi- 
tated to  separate  impurities.  It  is  safest  to  weigh  as  metallic  nickel.] 

To  determine  the  cobalt  in  the  filtrate,  supersaturate  with  acetic 
acid,  boil,  precipitate  the  boiling  solution  with  sulphate  of  copper, 
keep  in  ebullition  for  some  time  longer,  then  filter  the  fluid  from  the 
precipitated  cobalticyanide  of  copper  (Cu3  Co2  Cy6+  7 H O) ; decom- 
pose the  latter  by  boiling  with  solution  of  potassa,  and  calculate  the 


* Phil.  Mag.  16.  No  106,  197.  f Annal.  d.  Chem.  u.  Pharm.  43,  129. 
X Ibid.  65,  244,  and  87,  128. 

1 2 (Co  Cy,  K Cy)  + K Cy  + H Cy  = (K3  Co2  Cy6)  +H. 


368 


SEPARATION. 


quantity  of  the  cobalt  from  that  of  the  oxide  of  copper  obtained. 
[Or  evaporate  to  dryness  with  excess  of  hydrochloric  acid,  dissolve 
the  residue  in  water,  separate  the  cobalt  as  sulphide,  convert  into 
sulphate  and  oxide,  and  weigh  as  metallic  cobalt.  The  best  method 
of  separating  a little  nickel  from  much  cobalt.  (Gauhe.*)] 

c.  Protoxide  of  Nickel  from  Oxide  of  Zinc. 

Mix  the  concentrated  solution  of  both  oxides  with  an  excess  of  S3 
concentrated  pure  solution  of  potassa,  then  with  solution  of  hydro- 
cyanic acid  in  sufficient  quantity  to  redissolve  the  precipitate  com- 
pletely ; add  solution  of  monosulphide  of  potassium , allow  the  pre- 
cipitated sulphide  of  zinc  to  deposit  at  a gentle  heat,  filter,  and  de- 
termine the  nickel  in  the  filtrate  by  heating  for  some  time  with  fum- 
ing hydrochloric  acid  and  nitric  acid,  or,  instead  of  the  latter,  chlo- 
rate of  potassa,  evaporating,  and  finally  precipitating  with  potassa 
(Wohler|). 

12.  Volumetric  Determination  of  one  of  the  Oxides . 

a . Sesquioxide  of  Iron  from  Alumina. 

Precipitate  both  oxides  with  ammonia  (§  105,  a,  and  § 113,  1).  8 * 
Dissolve  the  weighed  residue,  or  an  aliquot  part  of  it,  by  digestion 
with  concentrated  hydrochloric  acid,  or  by  fusion  with  bisulphate  of 
potassa  [or  better,  carbonate  of  soda],  and  treatment  with  water  con- 
taining sulphuric  acid ; and  determine  the  iron  volumetrically  as  direc- 
ted § 113,  3,  a,  or  b.  When  hydrochloric  acid  is  used  to  dissolve 
the  oxides,  the  solution  should  be  evaporated  with  excess  of  sul- 
phuric acid,  to  remove  the  hydrochloric  acid,  in  case  permanganate  is 
employed  for  estimating  the  iron.  The  alumina  is  found  from  the 
difference.  This  is  an  excellent  method,  and  to  be  recommended 
more  particularly  in  cases  where  the  relative  amount  of  iron  is  small. 

If  you  have  enough  substance  it  is  of  course  much  more  convenient 
to  divide  the  solution,  by  weighing  or  measuring,  into  two  equal  por- 
tions, and  determine  in  the  one  the  sesquioxide  of  iron  -f-  alumina, 
in  the  other  the  iron.  Instead  of  estimating  the  iron  by  volumetric 
analysis,  you  may  also  precipitate  it,  after  addition  of  tartaric  acid 
and  ammonia,  with  sulphide  of  ammonium. 

b.  Sesquioxide  of  Iron  from  Protoxide  of  Iron  (Oxide  of 
Zinc,  Protoxide  of  Nickel). 

Determine  in  a portion  of  the  substance  the  total  amount  of  the  35 
iron  as  sesquioxide,  or  by  the  volumetric  way.  Dissolve  another  por- 
tion by  warming  with  sulphuric  acid  in  a flask  through  which  car- 
bonic acid  is  conducted,  to  exclude  the  air;  dilute  the  solution, 
and  determine  the  protoxide  of  iron  volumetrically  (§112,  2,  a).  The 
difference  gives  the  quantity  of  the  sesquioxide.  Or,  dissolve  the 
compound  in  like  manner  in  hydrochloric  acid,  and  determine  the 
sesquichloride  of  iron  with  hyposulphite  of  soda,  according  to  § 113, 

3,  b.  In  this  case  the  difference  gives  the  protoxide  of  iron.  If  it 
is  desired  to  determine  the  protochloride  of  iron  in  the  hydrochloric 
acid  solution  with  permanganate,  the  remarks  on  p.  198  must  be  borne 


* Fres.  Zeitschrift,  v.  83. 


f Annal.  d.  Chem.  u.  Pharm.  89,  376. 


§ 160.1 


BASES  OF  GROUP  IV. 


365 


in  mind.  These  convenient  and  simple  methods  deserve  to  replace  the 
older  and  more  complicated  methods  of  determining  protoxide  of  iron 
in  presence  of  sesquioxide.  If  the  compound  in  which  sesqui-  and 
protoxide  of  iron  are  to  be  estimated  is  only  with  difficulty  decom- 
posed by  acids,  heat  it  with  a mixture  of  4 parts  sulphuric  acid  and 
1 part  water  in  a sealed  tube  at  210°  (Mitscherlich,  Jour.  f. 
prakt.  Chem.,  81, 108,  and  83,  455),  or,  if  this  is  not  enough,  fuse  it  with 
borax  (1  part  mineral,  5 — 6 vitrified  borax)  in  a small  retort,  con- 
nected with  a flask  containing  nitrogen  (produced  by  combustion  of 
phosphorus  in  air)  ; an  atmosphere  of  carbonic  acid  is  less  suitable. 
Triturate  the  fused  mass,  and  dissolve  in  boiling  hydrochloric  acid, 
in  an  atmosphere  of  carbonic  acid  (Hermann;  v.  Kobell). 


Fig.  67. 


[Cooke*  dissolves  silicates  in  a mixture  of  sulphuric  and  hydro- 
fluoric acids  in  an  atmosphere  of  steam  and  carbonic  acid,  and  mea- 
sures the^ protoxide  of  iron  by  means  of  permanganate  of  potassa. 

Fig.  67  exhibits  his  apparatus.  To  the  sides  of  a copper  water- 
bath  are  attached  three  tubes.  The  tube  on  the  left  connects  with  a 
Mariotte’s  flask  to  maintain  the  water  at  a constant  level.  The  upper 
tube  on  the  right  connects  with  a carbonic  acid  gas  generator,  while 
the  third  tube  carries  off  any  overflow  of  water  to  the  sink. 

On  the  cover  of  the  water-bath  close  to  the  rim  is  a circular 
groove,  which  receives  the  edge  of  an  inverted  glass  tunnel.  When 
the  apparatus  is  in  use  this  groove  is  kept  full  of  water  by  the  spray 
from  the  boiling  liquid  and  thus  forms  a perfect  water  joint;  but  in 
order  to  secure  this  result  the  bath  must  be  kept  nearly  full  of  water 
and  holes  for  the  ready  escape  of  the  steam  and  spray  should  be  pro- 
vided in  the  rings,  which  cover  the  bath  and  adapt  it  for  vessels  of 
various  sizes.  By  this  arrangement  the  funnel  may  be  kept  filled  with 
an  atmosphere  of  steam  or  of  carbonic  acid  for  an  indefinite  period. 
Moreover  we  can  either  pour  in  fresh  quantities  of  solvent,  or  we 
can  stir  up  the  material,  in  the  vessel  within,  introducing  a tube-fun- 
nel or  stirrer  through  the  spout  of  the  covering  funnel. 

[*  Am.  Jour.  Science,  2d  ser.,  xliv  347.1 
24 


370 


SEPARATION. 


L§  161. 


The  finely  pulverized  substance  (| — 1 grm.)  is  placed  in  a large 
platinum  crucible.  Upon  it  pour  a mixture  of  dilute  sulphuric  acid 
(sp.  gr.  T5)  with  as  little  hydrofluoric  acid  as  experience  may  show 
is  required  to  dissolve  or  decompose  the  substance,  stirring  up  the 
material  with  a platinum  spatula.  The  crucible  is  next  transferred 
to  the  water-bath,  the  covering  funnel  put  in  place,  water  poured  into 
the  groove,  the  interior  filled  with  carbonic  acid,  and  the  lamp  lighted. 

As  soon  as  the  water  boils,  the  supply  of  carbonic  acid  is  stopped, 
and  if  the  water  level  has  been  properly  adjusted,  the  apparatus  will 
take  care  of  itself,  the  groove  will  be  kept  full  of  water  and  the  inter- 
ior of  the  funnel  full  of  steam.  If  the  materials  cake  on  the  bottom  of 
the  crucible, — as  is  not  unfrequently  the  case  when  a large  amount  of 
insoluble  sulphate  is  formed, — the  lamp  may  be  removed,  the  appara- 
tus again  filled  with  carbonic  acid,  and  the  contents  of  the  crucible 
stirred  up  by  aid  of  a stout  platinum  wire  about  two  inches  long, 
fused  to  the  end  of  a glass  tube.  Anything  adhering  to  the  rod  can 
easily  be  washed  back  into  the  crucible  by  directing  the  jet  from  the 
wash  bottle  down  the  throat  of  the  covering  funnel.  The  lamp  may 
then  be  replaced,  the  current  of  carbonic  acid  interrupted,  and  the 
process  of  digestion  continued.  When  the  decomposition  is  complete 
the  current  of  carbonic  acid  gas  is  re-established,  the  lamp  extinguished, 
and  the  air-tube  of  the  Mariotte’s  flask  raised  until  its  lower  end  is 
above  the  level  of  the  overflow.  A slow  current  of  water  is  thus 
caused  to  flow  through  the  bath,  which  soon  cools  down  the  whole 
apparatus.  The  crucible  may  now  be  removed,  its  contents  washed 
into  a beaker  glass,  and  the  solution  diluted  with  pure  water  until  the 
volume  is  about  500  c.  c.,  when  the  amount  of  protoxide  of  iron 
present  can  be  determined  with  a solution  of  permanganate  of  potassa 
in  the  usual  way.  The  total  amount  of  iron  present  being  subse- 
quently determined,  the  relative  proportion  of  the  two  oxides  is  of 
course  well  known.] 

Iron  may  also  be  determined  volumetrically  in  presence  of  oxide 
of  zinc,  protoxide  of  nickel,  &c.  It  is,  indeed,  often  the  better  way, 
instead  of  effecting  the  actual  separation  of  the  oxides,  to  determine 
in  one  portion  of  the  solution  the  sesquioxide  of  iron  -j-  oxide  of 
zinc  or  + protoxide  of  nickel,  in  another  portion  the  iron  alone,  and 
to  find  the  quantity  of  the  other  metal  by  the  difference.  However, 
this  can  be  done  only  in  cases  where  the  quantity  of  iron  is  relatively 
small. 

IY.  Separation  of  Sesquioxide  of  Iron,  Alumina,  Protoxide  of 
Manganese,  Lime,  Magnesia,  Potassa,  and  Soda. 

§ 16.1. 

As  these  oxides  are  found  together  in  the  analysis  of  most  silicates, 
and  also  in  many  other  cases,  I devote  a distinct  paragraph  to  the 
description  of  the  methods  which  are  employed  to  effect  their  sepa- 
ration. 

1.  Method  based  upon  the  employment  of  Carbonate  of  Jd ary ta 
(particularly  applicable  in  cases  where  the  mixture  contains 
only  a small  proportion  of  lime). 

Precipitate  the  iron — which  must  be  present  in  the  form  of  ses-  86 


161.] 


BASES  OF  GEOUP  IV. 


37! 


quioxide — and  the  alumina  by  carbonate  of  baryta,*  and,  after  re- 
moving the  baryta,  separate  the  two  metals,  by  one  of  the  methods 
given  in  § 160.  Precipitate  the  manganese  from  the  filtrate,  either 
by  yellow  sulphide  of  ammonium  (55)  or,  after  addition  of  a little 
hydrochloric  acid  and  saturation  with  chlorine,  by  carbonate  of  baryta 
(60)-  If  you  have  used  sulphide  of  ammonium,  which  I generally 
prefer,  dissolve  the  precipitated  sulphide  of  manganese  in  hydrochloric 
acid,  mix  the  solution  with  some  sulphuric  acid,  filter,  and  determine 
the  manganese  as  directed  § 109,  2 or  3.  If  you  have  used  carbon- 
ate of  baryta  as  precipitant,  separate  the  manganese  as  directed 
§ 159.  Precipitate  the  dilute  solution  now  with  sulphuric  acid,  filter, 
and  wash  the  precipitate  until  the  water  running  off  is  no  longer  ren- 
dered turbid  by  chloride  of  barium ; then  precipitate  the  lime  after 
addition  of  ammonia  with  oxalate  of  ammonia.  Filter,  evaporate 
the  filtrate  to  dryness,  ignite  the  residue,  and  separate  the  magnesia 
from  the  alkalies  by  one  of  the  methods  given  in  § 153. 

2.  Application  of  Alkaline  Acetates  or  Formiates. 

Remove  from  the  solution,  by  evaporation,  any  very  considerable  87 
excess  of  acid  which  may  be  present,  then  dilute  again  with  water, 
add  carbonate  of  soda,  f until  the  fluid  is  nearly  neutral  (no  per- 
manent precipitate  must  be  formed),  then  acetate  or  formiate  of 
soda,  and  proceed  as  in  § 113,  1,  d (p.  202).  Wash  the  precipitate 
well,  dry,  ignite,  and  weigh.  Dissolve  in  concentrated  hydrochloric 
acid,  and  determine  the  iron  volumetrically,  according  to  § 113,  3,  b 
(p.  203),  or  fuse  with  carbonate  of  soda,  dissolve  in  dilute  sulphuric 
acid,  and  determine  the  iron  as  in  § 1 13,  3 , a (p.  203).  The  difference 
gives  the  quantity  of  the  alumina.  If  any  silicic  acid  remains  be- 
hind on  dissolving  the  precipitate,  it  is  to  be  collected  on  a filter,  ig- 
nited, weighed,  and  deducted  from  the  alumina.  The  filtrate  contains 
the  manganese,  the  alkaline  earths,  and  the  alkalies.  Precipitate  the 
manganese  with  sulphide  of  ammonium  (55)  or  bromine  (59-61) — 
if  the  former  precipitant  is  employed,  boil  with  hydrochloric  acid  and 
filter  oft*  the  sulphur — precipitate  the  lime,  after  addition  of  ammo- 
nia, with  oxalate  of  ammonia,  and  lastly,  after  removing  the  ammo- 
nia salts  by  ignition,  precipitate  the  magnesia  from  the  hydrochloric 
acid  solution  of  the  residue  with  phosphate  of  soda.  However,  if  it 
is  intended  to  estimate  the  alkalies,  the  magnesia  must  be  separated 
by  one  of  the  processes  in  § 153,  4.  This  method  is  convenient,  and 
gives  good  results. 

The  following  methods  are  particularly  suitable  in  cases  where  no 
manganese  is  present. 

3.  Application  of  Ammonia . 

The  solution  must  contain  all  the  iron  in  the  state  of  sesquioxide.  88 
Add  a relatively  large  quantity  of  chloride  of  ammonium,  and — ob- 
serving the  precautions  indicated  in  68 — precipitate  with  ammonia. 


* Before  adding  the  carbonate  of  baryta,  it  is  absolutely  indispensable  to  ascer- 
tain whether  a solution  of  it  in  hydrochloric  acid  is  completely  precipitated  by 
sulphuric  acid,  so  that  the  filtrate  leaves  no  residue  upon  evaporation  in  a plati- 
num dish. 

f In  cases  where  it  is  intended  to  estimate  the  alkalies  in  the  filtrate,  carbonate 
and  acetate  of  ammonia  must  be  used  instead  of  the  soda  salts. 


372 


SEPARATION. 


[§  161. 


The  precipitate  contains  the  whole  of  the  iron  and  almost  the  whole 
of  the  alumina  (a  very  minute  quantity  of  the  latter  often  remains 
in  solution),  also  a trace  of  magnesia.  Decant  and  filter ; wash,  ignite, 
and  weigh  the  precipitate,  and  treat  according  to  one  of  the  methods  in 
§ 160.  If  silicic  acid  remains  undissolved,  it  is  to  be  determined  and 
deducted.  If  there  is  a large  excess  of  alumina  or  magnesia,  mix  the 
hydrochloric  acid  or  sulphuric  acid  solution  with  pure  potassa  in  excess, 
heat,  filter,  and  in  the  precipitate  separate  the  sesquioxide  of  iron  from 
any  traces  of  magnesia  that  may  be  present  according  to  58,  The  so- 
lution filtered  from  the  alumina  and  sesquioxide  of  iron  is  mixed  with 
hydrochloric  acid  and  concentrated  by  evaporation,  the  manganese  is 
precipitated  and  determined  according  to  § 109,  2,  as  sulphide,  the  alka- 
line earths  and  alkalies  in  the  filtrate  are  estimated  according  to  87* 
The  weighed  sulphide  of  manganese  is  digested  with  hydrochloric 
acid,  any  residue  that  may  remain  fused  with  bisulphate  of  potassa, 
and  the  mixed  solutions  tested  according  to  66,  to  see  if  they  con- 
tain alumina. 

4.  Decomposition  of  the  Nitrates  (Deville’s  method). 

This  method  presupposes  that  the  bases  are  combined  with  nitric  89 
acid  only. 

Proceed  first  as  in  38.  The  escape  of  nitrous  acid  fumes,  observed 
during  the  heating  of  the  nitrates,  is  no  proof  of  the  total  decompo- 
sition of  the  nitrates  of  sesquioxide  of  iron  and  alumina,  as  these 
vapors  may  owe  their  formation  to  the  conversion  of  the  nitrate  of 
protoxide  of  manganese  into  binoxide.  Stop  the  application  of  heat 
when  no  more  vapors  are  evolved,  and  the  substance  has  acquired  a 
uniform  black  color.  After  the  treatment  with  nitrate  of  ammonia, 
the  solution  contains  nitrates  of  lime,  magnesia,  and  the  alkalies,  the 
residue  contains  alumina,  sesquioxide  of  iron  and  binoxide  of  man- 
ganese. (That  some  manganese  is  dissolved,  under  certain  circum- 
stances, has  been  stated  already  in  62 ; this  trace  is  found  with  the 
magnesia,  and  finally  separated  from  the  latter.) 

Deville  recommends  the  following  methods  to  effect  the  further 
separation  of  the  bases: — 

a.  Heat  the  residue  with  moderately  strong  nitric  acid,  until  the 
alumina  and  sesquioxide  of  iron  are  dissolved,  leaving  the  residuary 
binoxide  of  manganese  of  a pure  black  color.  Ignite  the  residue,  and 
weigh  the  protosesquioxide  of  manganese  formed.  Evaporate  the 
solution  in  a platinum  crucible,  ignite,  and  weigh  the  mixture  of  ses- 
quioxide of  iron  and  alumina,  which  may  possibly  also  contain  some 
protosesquioxide  of  manganese.  Treat  a portion  of  it  by  the  method 
described  in  75;  this  gives  the  alumina.  If  manganese  was  present, 
the  iron  cannot  be  estimated  by  difference.  Deville  therefor  e eva- 
porates the  solution  of  the  protochlorides  (75),  with  sulphuric 
acid,  ignites  gently,  and  treats  the  residue,  which  consists  of  ses- 
quioxide of  iron  and  some  sulphate  of  protoxide  of  manganese,  with 
water  to  dissolve  the  latter.  (Should  the  heat  applied  have  been  too 
strong,  which  might  possibly  lead  to  the  decomposition  also  of  sulphate 
of  protoxide  of  manganese,  the  residue  is  moistened  with  a mixture 
of  oxalic  acid  and  nitric  acid,  some  sulphuric  acid  added,  and  the 
process  repeated.) 

b.  From  the  filtrate,  precipitate  first  the  lime  by  oxalate  of 


BASES  OF  GROUP  IV. 


373 


§ 161.] 


ammonia,  then  separate  the  magnesia  from  the  alkalies  as  directed 

§ 153,  4- 

This  method  is  particularly  suitable  in  the  absence  of  manganese. 

5.  Method  which  combines  3 arid  4. 

Precipitate  with  ammonia  (37)>  decant,  filter,  wash,  remove  the  90 
still  half-moist  precipitate,  as  far  as  practicable,  from  the  filter,  dis- 
solve the  rest  in  nitric  acid,  transfer  this  to  the  dish,  to  effect  also 
the  solution  of  the  bulk  of  the  precipitate ; proceed  as  in  89?  and 
add  the  fluid,  separated  from  the  sesquioxide  of  iron  and  alumina, 
and  still  containing  small  quantities  of  magnesia,  to  the  principal 
filtrate.  This  method  is  often  employed  with  the  best  success  in 
my  laboratory,  in  absence  of  manganese;  the  determination  of  the 
alumina  being  effected  by  estimating  the  total  amount  of  ses- 
quioxide of  iron  and  alumina,  then  the  sesquioxide  of  iron  volumet- 
rically  (87)* 


Supplement  to  the  Fourth  Group. 

To  §§  158,  159,  160. 

Separation  of  Sesquioxide  of  Uranium  from  the  other 
Oxides  of  Groups  I. — IV. 

It  has  already  been  stated,  in  § 114,  that  sesquioxide  of  uranium  91 
•cannot  be  completely  separated  from  the  alkalies  by  means  of  am- 
monia, as  the  precipitated  ammonio-sesquioxide  of  uranium  is  likely 
to  contain  also  fixed  alkalies.  This  precipitate  should  therefore  be 
dissolved  in  hydrochloric  acid,  the  solution  evaporated  in  the 
platinum  crucible,  the  residue  gently  ignited  in  a current  of  hydro- 
gen gas  (see  fig.  47,  p.  181),  the  chlorides  of  the  alkali  metals  ex- 
tracted with  water,  and  the  protoxide  of  uranium  ignited  in  hydro- 
gen, in  order  to  its  being  weighed  as  such,  or  in  the  air,  whereby  it 
is  converted  into  protosesquioxide.  Instead  of  dissolving  the  pre- 
cipitate in  hydrochloric  acid  and  treating  the  solution  as  directed, 
you  may  heat  the  precipitate  cautiously*  with  chloride  of  ammonium, 
and  treat  the  residue  with  water  (H.  Rose). 

From  baryta. , sesquioxide  of  uranium  may  be  separated  by 
sulphuric  acid,  from  strontia  and  lime,  by  sulphuric  acid  and  alco- 
hol. Ammonia  fails  to  effect  complete  separation  of  sesquioxide  of 
uranium  from  the  alkaline  earths,  the  uranium  precipitate  always 
containing  not  inconsiderable  quantities  of  the  earths.  In  such 
precipitates,  however,  the  uranium  and  the  alkaline  earth  may  like- 
wise be  separated  by  gentle  ignition  with  chloride  of  ammonium 
and  treatment  of  the  residue  with  water. 

Uranium  may  be  precipitated  from  a solution  containing  alkalies  92 
and  alkaline  earths  also  by  sulphide  of  ammonium.  It  must  here  be 
borne  in  mind  that  the  solution  must  contain  a sufficiency  of  chloride 
of  ammonium  and  free  ammonia,  that  the  precipitate  must  not  be 
filtered  off  till  after  long  standing  (24 — 48  hours)  in  the  closed  flask, 
and  that  no  alkaline  carbonate  may  be  present.  The  sulphide  of  am- 
monium should  be  colorless,  or  slightly  yellow,  and  a large  excess 


* Strong  ignition  would  occasion  the  volatilization  of  chloride  of  uranium. 


374 


SEPARATION. 


[§  161. 


should  be  avoided.  The  color  of  the  precipitate  varies,  being  some- 
times dirty  yellow,  sometimes  brown,  reddish-brown,  or  black,  ac- 
cording to  the  proportions  of  chloride  of  ammonium,  ammonia,  and 
sulphide  of  ammonium,  for  it  is  not  the  sulphide  corresponding  to  the 
sesquioxide,  but  consists  of  uranium,  oxygen,  ammonium,  sulphur 
and  water  (Patera).  Wash  the  precipitate  with  water  containing 
sulphide  of  ammonium,  dry,  roast  it  for  some  time,  ignite  strongly  in 
an  atmosphere  of  hydrogen,  allow  to  cool  in  a rapid  stream  of  the 
same  gas,  and  weigh  the  residual  protoxide  of  uranium  (H.  Pose).  If 
the  quantity  of  the  alkalies  or  alkaline  earths  that  are  to  be  separated 
from  the  uranium  is  large,  in  order  to  effect  complete  separation,  re- 
dissolve the  washed  precipitate  in  hydrochloric  acid,  and  repeat  the 
precipitation  with  sulphide  of  ammonium. 

Magnesia  may  also  be  separated  from  sesquioxide  of  uranium  by  9 3 
ammonia.  Add  enough  chloride  of  ammonium  to  the  solution,  heat 
to  boiling,  supersaturate . with  ammonia,  continue  boiling,  till  the 
odor  of  ammonia  is  but  slight,  filter  the  hot  fluid,  and  wash  the  pre- 
cipitate, which  is  free  from  magnesia,  with  hot  water  containing  am- 
monia (H.  Pose). 

Alumina  is  best  separated  from  sesquioxide  of  uranium  by  mixing 
the  somewhat  acid  fluid  with  carbonate  of  ammonia  in  excess.  The 
sesquioxide  of  uranium  passes  completely  into  solution,  while  the 
alumina  remains  absolutely  undissolved.  Filter,  evaporate,  add  hy- 
drochloric acid  to  resolution  of  the  precipitate  produced,  heat  till  all 
the  carbonic  acid  is  expelled,  and  precipitate  with  ammonia  (§  114). 

The  separation  of  uranium  from  the  metals  of  the  fourth  group  94 
may  be  based  simply  on  the  fact  that  carbonate  of  ammonia  prevents 
the  precipitation  of  uranium  but  not  that  of  the  other  metals  by  sul- 
phide of  ammonium.  Mix  the  solution  with  a mixture  of  carbonate 
of  ammonia  and  sulphide  of  ammonium,  allow  to  subside  in  a closed 
flask  and  wash  the  precipitate  with  water  containing  carbonate  of 
ammonia  and  sulphide  of  ammonium.  Supersaturate  the  filtrate  cau- 
tiously with  hydrochloric  acid,  heat  with  addition  of  nitric  acid,  to 
convert  the  proto-  into  sesquioxide  of  uranium  and  precipitate  with 
ammonia  (H.  Pose  *). 

Sesquioxide  of  iron  may  be  also  separated  from  sesquioxide  of  ura- 
nium by  means  of  an  excess  of  carbonate  of  ammonia.  The  small 
quantity  of  iron  which  passes  with  the  uranium  into  solution,  is  pre- 
cipitated with  sulphide  of  ammonium,  before  the  uranium  is  thrown 
down  (PiSANif). 

F rom  protoxides  of  nickel , cohalt , and  manganese , oxide  of  zinc  and 
magnesia , the  sesquioxide  of  uranium  may  also  be  separated  by  car- 
bonate of  baryta.  The  fluid,  which  should  contain  a little  free  acid, 
is  mixed  with  the  precipitant  in  excess,  and  allowed  to  stand  in  the 
cold  for  24  hours  with  frequent  shaking  (64)» 


* Zeitschrift  f.  analyt.  Chem.  1,  412. 


f Compt.  rend.  52,  106. 


§ 162.] 


BASES  OF  GROUP  V. 


375 


FIFTH  GROUP. 

OXIDE  OF  SILVER SUBOXIDE  OF  MERCURY OXIDE  OF  MERCURY OXIDE 

OF  LEAD PEROXIDE  OF  BISMUTH OXIDE  OF  COPPER OXIDE  OF 

CADMIUM. 

I.  Separation  of  the  Oxides  of  the  Fifth  Group  from  those  of 
the  first  Four  Groups. 

§162. 

Index  : — The  Nos.  refer  to  those  in  the  margin. 

Oxide  of  silver  from  the  oxides  of  Groups  I. — IV.,  95,  96. 

Oxide  and  suboxide  of  mercury  from  the  oxides  of  Groups  I.  — IY.  ,123,97. 

Oxide  of  lead  from  the  oxides  of  Groups  I. — IV.,  95,  98. 

Teroxide  of  bismuth  from  the  oxides  of  Groups  I. — IV.,  95,  98. 

Oxide  of  copper  from  the  oxides  of  Groups  I. — IV.,  95,  99,  100. 

“ “ oxide  of  zinc,  101. 

Oxide  of  cadmium  from  the  oxides  of  Groups  I. — IV.,  95. 

“ “ oxide  of  zinc,  103. 

A.  General  Method. 

All  the  Oxides  of  the  Fifth  Group  from  those  of  the  first 

Four  Groups. 

Principle  : Sulphuretted  Hydrogen  precipitates  from  Acid  Solu- 
tions the  Metals  of  the  Fifth  Group , hut  not  those  of  the  first  Four 
Groups. 

The  following  points  require  especial  attention  in  the  execution  of  95 
the  process : — 

a.  To  effect  the  separation  of  the  oxides  of  the  fifth  group  from 
those  of  the  first^three  groups,  by  means  of  sulphuretted  hydrogen,  it 
is  necessary  simply  that  the  reaction  of  the  solution  should  be  acid, 
the  nature  of  the  acid  to  which  the  reaction  is  due  being  of  no  con- 
sequence. But,  to  effect  the  separation  of  the  oxides  of  the  fifth 
group  from  those  of  the  fourth,  the  presence  of  a free  mineral  acid 
is  indispensable ; otherwise,  zinc  and,  under  certain  circumstances, 
also  cobalt  and  nickel  may  be  coprecipitated. 

/3.  But  even  the  addition  of  hydrochloric  acid  to  the  fluid  will  not 
always  entirely  prevent  the  coprecipitation  of  the  zinc.  Rivot  and 
Bouquet*  declare  a complete  separation  of  copper  from  zinc  by  means 
of  sulphuretted  hydrogen,  altogether  impracticable.  Calvert|  states 
that  he  has  arrived  at  the  same  conclusion.  On  the  other  hand, 
SpirgatisJ  concurs  with  H.  Rose  in  maintaining  that  complete  sep- 
aration of  copper  from  zinc  may  be  effected  by  means  of  sulphuretted 
hydrogen,  in  presence  of  a sufficient  quantity  of  free  acid. 

In  this  conflict  of  opinions,  I thought  it  necessary  to  subject  this 
method  once  more  to  a searching  investigation.  I therefore  instructed 
one  of  the  students  in  my  laboratory,  Mr.  Grundmann,  to  make  a 
series  of  experiments  in  the  matter,  with  a view  to  settling  the  question.  j| 

The  results  obtained  proved  incontestably  that  copper  may  be 
completely  separated  from  zinc  by  sulphuretted  hydrogen,  if  the  fol- 
lowing instructions  are  strictly  complied  with  : — 

Add  to  the  copper  and  zinc  solution  a copious  amount  of  hydro- 
chloric acid  ( e . g .,  to  0‘2  grm.  of  oxide  of  copper  in  25  c.  c.  of  solu- 
tion, 10  c.  c.  of  hydrochloric  acid  of  IT  sp.  gr.),  conduct  into  the  fluid 

* Annal.  d.  Chem.  u.  Pharm.  80,  364. 

f Joum.  f.  prakt.  Chem.  71,  155.  \ Ibid.  58,  351.  1 Ibid.  73,  241. 


376 


SEPARATION. 


[§  162 

sulphuretted  hydrogen  largely  in  excess,  filter  before  the  excess  of 
sulphuretted  hydrogen  has  had  time  to  escape  or  become  decomposed, 
wash  with  sulphuretted  hydrogen  water,  dry,  roast,  redissolve  in  ni- 
trohydrochloric  acid,  evaporate  nearly  to  dryness,  add  water  and  hy- 
drochloric acid  as  above,  and  precipitate  again  with  sulphuretted 
hydrogen.  This  second  precipitate  is  free  from  zinc ; it  is  treated  as 
directed  in  § 119,  3 (p.  230). 

If  cadmium  is  present,  a portion  of  this  metal  is  likely  to  remain  in 
solution,  in  presence  of  the  large  amount  of  hydrochloric  acid  added. 

It  is  therefore  necessary,  in  that  case,  after  conducting  the  sulphur- 
etted hydrogen  gas  into  the  fluid,  to  add  saturated  sulphuretted  hy- 
drogen water  until  no  more  sulphide  of  cadmium  precipitates,  and 
then  to  proceed  as  for  the  separation  of  copper.  The  separation  of 
cadmium  from  zinc  requires  accordingly  also  a double  precipitation 
with  sulphuretted  hydrogen,  if  the  quantity  of  zinc  is  in  any  way 
considerable.  However,  with  proper  attention  to  the  instructions 
here  given,  the  method  gives  perfectly  satisfactory  results. 

y.  The  other  metals  of  the  fifth  group  comport  themselves  in  this 
respect  similarly  to  cadmium,  i.  e.,  they  are  not  completely  precipi- 
tated by  sulphuretted  hydrogen  in  presence  of  too  much  free  acid  in 
a concentrated  solution.  Lead  requires  the  least  amount  of  free  acid 
to  be  retained  in  solution ; then  follow  in  order  of  succession,  cadmi- 
um, mercury,  bismuth,  copper,  silver  (M.  Martin*).  The  separa- 
tion of  these  metals  from  zinc  must,  therefore,  if  necessary,  be 
effected  by  the  same  process  as  that  of  cadmium  from  zinc  (|3,  the  end). 

(5.  If  hydrochloric  acid  produces  no  precipitate  in  the  solution,  it 
is  preferred  as  acidifying  agent ; in  the  contrary  case,  sulphuric  acid 
or  nitric  acid  must  be  used.  In  the  latter  case  the  fluid  must  be 
rather  largely  diluted.  Eliot  and  STORERf  arrived  at  the  same 
conclusion  as  ourselves,  and  showed  that  the  cause  of  Calvert’s  unfa- 
vorable results  was  the  too  large  dilution  of  his  solutions.  For  to 
prevent  the  precipitation  of  zinc  you  have  not  merely  to  preserve  a 
certain  proportion  between  the  zinc  and  the  free  acid,  but  also  a cer- 
tain degree  of  dilution.  Although  I agree  with  the  above-named 
chemists  in  the  opinion  that  it  is  possible  to  produce  a condition  of 
the  fluid,  under  which  one  precipitation  will  effect  complete  separa- 
tion, still  it  appears  to  me  better,  for  practical  purposes,  to  precipi- 
tate twice,  as  this  is  sure  to  lead  to  the  desired  result. 

s.  Long  experience  in  the  separation  of  copper  from  nickel  (and  co- 
balt) has  led  me  to  the  opinion  that  a double  precipitation  is  unneces- 
sary. If  the  solution  which  is  to  be  treated  with  sulphuretted  hydrogen 
contains  enough  free  hydrochloric  acid  and  not  too  much  water,  the 
copper  falls  down  absolutely  free  from  nickel,  while,  on  the  other  hand, 
if  the  quantity  of  free  acid  is  not  too  large,  the  filtrate  will  be  quite  free 
from  copper. 

B.  Special  Methods. 

Single  Oxides  of  the  Fifth  Group  from  Single  or  Mixed 
Oxides  of  the  First  Four  Groups. 

1.  Silver  is  most  simply  and  completely  separated  from  the  oxides  96 

* Joum.  f.  prakt.  Chem.  67,  371. 

\ On  the  Impurities  of  Commercial  Zinc,  &c. — Memoirs  of  the  American 
Academy  of  Arts  and  Sciences.  New  series.  Vol.  viii. 


BASES  OF  GROUP  V. 


377 


162.] 


OF  the  first  four  groups  by  means  of  hydrochloric  acid.  The  hy- 
drochloric acid  must  not  be  used  too  largely  in  excess,  and  the  fluid 
must  be  sufficiently  dilute ; otherwise  a portion  of  the  silver  will  re- 
main in  solution.  Care  must  be  taken  also  not  to  omit  the  addition 
of  nitric  acid,  which  promotes  the  separation  of  the  chloride  of  silver. 
The  latter  should,  under  these  circumstances,  be  collected  and  washed 
on  a filter  (p.  208  /?),  as  washing  by  decantation  would  give  too  large 
a bulk  of  fluid. 

2.  The  separation  of  Mercury  from  the  metals  of  the  first  four  97 
groups  may  be  effected  also  by  ignition,  which  will  cause  the  volati- 
lization of  the  mercury  or  the  mercurial  compound,  leaving  the  non- 
volatile bodies  behind.  The  method  is  applicable  in  many  cases  to 
alloys,  in  others  to  oxides,  chlorides,  or  sulphides.  If  the  mercury  is 
estimated  only  from  the  loss,  the  operation  is  conducted  in  a crucible ; 
otherwise  in  a bulb-tube,  or  a wide  glass  tube  with  porcelain  boat. 

The  precipitation  of  mercury  as  subchloride  with  phosphorous  acid, 
according  to  § 118,  2 (p.  224)  is  also  well  adapted  for  its  separation 
from  metals  of  Group  IV.  If  the  mercury  is  already  present  as  sub- 
oxide, it  may  be  separated  and  determined  in  a simple  manner,  by 
precipitation  with  hydrochloric  acid  (§  117,  1). 

3.  From  those  Bases  which  form  soluble  salts  with  sul-  98 
phuric  acid,  oxide  of  lead  may  be  readily  separated  by  that  acid. 
The  results  are  very  satisfactory,  if  the  rules  given  in  § 116,  3,  are 
strictly  adhered  to. 

If  you  have  lead  in  presence  of  baryta,  both  in  form  of  sulphates, 
digest  the  precipitate  with  a solution  of  ordinary  sesquicarbonate  of 
ammonia,  without  application  of  heat.  This  decomposes  the  lead 
salt,  leaving  the  baryta  salt  unaltered.  Wash,  first  with  solution  of 
carbonate  of  ammonia,  then  with  water,  and  separate  finally  the  car- 
bonate of  lead  from  the  sulphate  of  baryta,  by  acetic  acid  or  dilute 
nitric  acid  (H.  Bose*).  The  same  object  may  also  be  attained  by 
suspending  the  washed  insoluble  salts  in  water  and  digesting  with  a 
clear  concentrated  solution  of  hyposulphite  of  soda  at  15 — 20°  (not 
higher).  The  sulphate  of  baryta  remains  undissolved,  the  sulphate 
of  lead  dissolves.  Determine  the  lead  in  the  filtrate  (after  § 116, 

2)  as  sulphide  of  lead  (J.  Lowe  f). 

4.  Oxide  of  Copper  from  all  Oxides  of  the  first  Four 
Groups. 

a.  Acidify  the  solution  with  sulphuric  acid,  and  precipitate  the  99 
copper  according  to  § 119,  l,c,  with  hyposulphite  of  soda, \ as  subsul- 
phide, and  determine  it  as  such  according  to  § 119,  3.  The  filtrate 
contains  the  other  bases.  Evaporate,  with  addition  of  nitric  acid, 
filter  and  determine  the  other  oxides  in  the  filtrate.  ||  Results  good. 


* Journ.  f.  prakt.  Chem.  66,  166.  f Ibid.  77,  75. 

\ The  commercial  salt  is  often  not  sufficiently  pure  ; in  which  case  some 
carbonate  of  soda  must  be  added  to  its  solution,  and  the  mixture  filtered. 

||  As  far  back  as  1842,  C.  Himly  made  the  first  proposal  to  employ  hyposul- 
phite of  soda  for  the  precipitation  of  many  metals  as  sulphides  (Anna!  d.  Chem. 
u Pharm.  43,  150).  The  question,  after  long  neglect,  was  afterwards  taken  up 
again  by  Vohl.  (Anna!  d.  Chem.  u.  Pharm.  96,  237),  and  Slater  (Chem.  Gaz. 
1855,  369).  Flajolot,  however,  made  the  first  quantitative  experiments  (Annal. 
des  Mines,  1853,  641  ; Journ.  f.  prakt.  Chem.  61,  105).  The  results  obtained  by 
him  are  perfectly  satisfactory. 


378 


SEPARATION. 


[§  162. 


It  has  been  stated  in  § 119, 1,  c,  that  the  solution  ought  to  be  free 
from  hydrochloric  and  nitric  acids  ; however,  this  is  not  absolutely 
necessary ; only,  in  presence  of  hydrochloric  or  nitric  acid,  a much 
larger  proportion  of  the  precipitant  is  required — in  presence  of  the 
former,  because  the  subchloride  of  copper  formed  is  decomposed 
only  by  a large  excess  of  hyposulphite  of  soda ; in  presence  of  the 
latter,  because  the  precipitant  begins  to  act  upon  the  copper  salt 
only  after  the  decomposition  of  the  nitric  acid. 

b.  Precipitate  the  copper  as  subsulphocyanide  according  to  § 119,  100 
3,  b ‘ the  other  metals  remain  in  solution  (Pivot).  If  alkalies  were 
present  and  it  were  desired  to  determine  them  in  the  filtrate,  sul- 
phocyanide  of  ammonium  must  be  used  instead  of  the  potassium 
salt  usually  employed.  This  method  is  particularly  well  adapted 
for  the  separation  of  copper  from  zinc.  The  zinc  can  be  precipitated 
at  once  from  the  filtrate  by  carbonate  of  soda.  The  method  is  also 
suitable  for  separating  copper  from  iron  (H.  Pose*)  ; in  this  case  it 
is  unnecessary  that  the  sesquioxide  of  iron  be  completely  reduced  by 
the  sulphurous  acid  added ; the  separation  may  be  eifected,  even  if 
the  solution  becomes  blood-red  on  the  addition  of  the  precipitant. 

5.  Oxide  of  Copper  from  Oxide  of  Zinc. 

BoBiERREf  employed  the  following  method  with  satisfactory  101 
results  in  the  analysis  of  many  alloys  of  zinc  and  copper: — The 
alloy  is  put  into  a small  porcelain  boat  lying  in  a porcelain  tube, 
and  heated  to  redness  for  three-quarters  of  an  hour  at  the  most,  a 
rapid  stream  of  hydrogen  gas  being  conducted  over  it  during  the 
process.  The  zinc  volatilizes,  the  copper  remains  behind.  Lead 
also  (if  that  metal  be  present)  is  not  volatilized  in  this  process. 

6.  Teroxide  of  Bismuth  from  the  Oxides  of  the  first  Four 
Groups,  with  the  exception  of  Sesquioxide  of  Iron. 

Precipitate  the  bismuth  according  to  § 120,  4 (p.  234),  as  basic  102 
chloride,  and  determine  it  as  metal ; all  the  other  bases  remain 
completely  in  solution.  Pesults  very  satisfactory  (H.  Pose  J). 

7.  Oxide  of  Cadmium  from  Oxide  of  Zinc. 

Prepare  a hydrochloric  or  nitric  acid  solution  of  the  two  ox- 103 
ides  as  neutral  as  possible,  add  a sufficient  quantity  of  tartaric  acid, 
then  solution  of  potassa  or  soda,  until  the  reaction  of  the  clear 
fluid  is  distinctly  alkaline.  Dilute  now  with  a sufficient  quantity 
of  water,  and  boil  for  1J — 2 hours.  All  the  cadmium  precipitates 

as  hydrated  oxide  free  from  alkali  (to  be  determined  as  directed  § 

121),  whilst  the  whole  of  the  zinc  remains  in  solution;  the  latter 
metal  is  determined  as  directed  in  § 108,  1,  b (Aubel  and  Pam- 
dohr||).  The  test-analyses  communicated  are  satisfactory. 


* Pogg.  Annal.  110,  424. 

f Compt.  rend.  36,  224 ; Joum.  f.  prakt.  Chem.  58,  380, 
% Pogg.  Annal.  110,  429. 

| Annal  d.  Chem.  u.  Pharm.  103,  33. 


§ 163.J 


BASES  OF  GROUP  V. 


379 


II.  Separation  of  the  Oxides  of  the  Fifth  Group 

FROM  EACH  OTHER. 


§163. 

Index  : — The  Nos.  refer  to  those  in  the  margin. 

Oxide  of  silver  from  oxide  of  copper,  104,  110,  111,  112,  122,  123,  124. 
“ oxide  of  cadmium,  104,  110,  112, 

“ teroxide  of  bismuth,  104,  109,  112,  113. 

“ oxide  of  mercury,  104,  110,  112,  117,  119,  141. 

“ oxide  of  lead,  104,  107,  108, 109, 112,  123, 124. 

Oxide  of  mercury  from  oxide  of  silver,  104,  110,  112,  117,  119,  141. 

“ suboxide  of  mercury,  105. 

“ oxide  of  lead,  106,  108,  109,  112,  117,  119. 

“ teroxide  of  bismuth,  109,  112,  117. 

“ oxide  of  copper,  106,  111,  112,  117,  119. 

“ oxide  of  cadmium,  106,  117. 

Suboxide  of  mercury  from  oxide  of  mercury,  105. 

“ oxide  of  copper,  105,  106,  119. 

“ oxide  of  cadmium,  105,  106. 

“ oxide  of  lead,  105,  106,  108,  109,  119. 

Compare,  also,  oxide  of  mercury  from  the  other  metals. 

Oxide  of  lead  from  oxide  of  silver,  104,  108,  109,  112,  122,  123,  124. 

“ oxide  of  mercury,  104,  107,  108,  109,  112,  117,  119. 

“ oxide  of  copper,  108,  109,  112,  114. 

“ teroxide  of  bismuth,  108,  114,  120,  121. 

“ oxide  of  cadmium,  108,  109,  112. 

Teroxide  of  bismuth  from  oxide  of  silver,  104,  109,  112,  120. 

“ oxide  of  lead,  108,  114,  120, 121 

“ oxide  of  copper,  109,  112, 113,  120. 

“ oxide  of  cadmium,  109,  112,  113,  114,  116. 

“ oxide  of  mercury,  109,  112,  117 

Oxide  of  copper  from  oxide  of  silver,  104,  110,  111,  112,  122,  123,  124, 

“ oxide  of  lead,  108, 109,  112, 114. 

“ teroxide  of  bismuth,  109,  112,  113,  120. 

“ oxide  of  mercury,  106,  111,  112,  117,  119. 

“ oxide  of  cadmium,  111,  112, 114,  115,  118. 

Oxide  of  cadmium  from  oxide  of  silver,  104,  110,  112. 

“ oxide  of  lead,  108,  109,  112. 

“ teroxide  of  bismuth,  109, 112,  113,  114,  116. 

“ oxide  of  copper,  111,  112, 114,  115,  118. 

“ oxide  of  mercury,  106,  117. 


1.  Methods  based  upon  the  Insolubility  of  certain  of  the  Chlo- 
rides. 

a.  Oxide  of  Silver  from  Oxide  of  Copper,  Oxide  of  Cadmium, 
Teroxide  of  Bismuth,  Oxide  of  Mercury,  and  Oxide  of  Lead. 

a.  To  separate  oxide  of  silver  from  oxide  of  copper , oxide  of  cad-  104c 
mium , and  teroxide  of  bismuth , add  to  the  nitric  acid  solution  con- 
taining excess  of  nitric  acid,  hydrochloric  acid  as  long  as  a precipi- 
tate forms,  and  separate  the  precipitated  chloride  of  silver  from  the 
solution  which  contains  the  other  oxides,  as  directed  § 115, 1,  a. 

0.  If  you  wish  to  separate  oxide  of  mercury  from  oxide  of  silver 
by  hydrochloric  acid,  special  precautions  must  be  taken,  as  a solution 
of  nitrate  of  mercury  possesses  the  property  of  dissolving  chloride 
of  silver  (Wackenroder,  v.  Liebig*).  Although  the  chloride  of 


* Annal.  d.  Chem.  u.  Pharm.  81,  128. 


380 


SEPARATION. 


[§  163. 


silver  in  solution  for  the  most  part  separates  on  the  addition  of 
enough  hydrochloric  acid  to  convert  the  nitrate  of  mercury  into 
chloride,  or  on  addition  of  acetate  of  soda,  still  we  cannot  depend 
upon  the  complete  precipitation  of  the  silver.  On  this  account, 
mix  the  nitric  acid  solution — which  may  not  contain  any  suboxide 
of  mercury,  and  is  to  be  in  a sufficiently  dilute  condition  and  acidi- 
fied with  nitric  acid — with  hydrochloric  acid,  as  long  as  a precipi- 
tate forms.  Allow  to  deposit,  filter  off  the  clear  fluid,  heat  the  pre- 
cipitate— to  free  it  from  any  possibly  coprecipitated  basic  mercury 
salts — with  a little  nitric  acid,  add  water,  then  a few  drops  of  hy- 
drochloric acid,  and  filter  off  the  chloride  of  silver.  In  the  filtrate 
determine  the  mercury  as  sulphide  (§  118,  3),  and  finally  test  this 
for  silver,  by  ignition  in  a stream  of  hydrogen — any  silver  that 
may  happen  to  be  present  will  remain  behind  in  the  metallic  state. 

y.  In  the  separation  of  silver  from  lead , the  precipitation  is  also 
preceded  by  addition  of  acetate  of  soda.  The  fluid  must  be  hot 
and  the  hydrochloric  acid  rather  dilute  ; no  more  must  be  added  of 
the  latter  than  is  just  necessary.  In  this  manner  the  separation 
may  be  readily  effected,  since  chloride  of  lead  dissolves  in  acetate 
of  soda  (Anthon).  The  lead  is  thrown  down  from  the  filtrate  by 
sulphuretted  hydrogen. 

S.  The  volumetric  method  (§  115,  5)  is  usually  resorted  to  in 
the  mint  to  determine  the  silver  in  alloys.  In  presence  of  oxide  of 
mercury,  acetate  of  soda  is  mixed  with  the  fluid  immediately  before 
the  addition  of  the  solution  of  chloride  of  sodium. 

b.  Suboxide  of  Mercury  from  Oxide  of  Mercury,  Oxide  of 
Copper,  Oxide  of  Cadmium,  and  Oxide  of  Lead. 

Mix  the  highly  dilute  cold  solution  with  hydrochloric  acid,  as  10  5 
long  as  a precipitate  (subchloride  of  mercury)  forms  ; allow  this  to 
deposit,  filter  on  a weighed  filter,  dry  at  100°,  and  weigh.  The 
filtrate  contains  the  other  oxides.  If  you  have  to  analyse  a solid 
body,  insoluble  in  water,  either  treat  directly,  in  the  cold,  with 
dilute  hydrochloric  acid,  or  dissolve  in  highly  dilute  nitric  acid, 
and  mix  the  solution  with  a large  quantity  of  water  before  pro- 
ceeding to  precipitate.  Care  must  always  be  taken  that  the  mode 
of  solution  is  such  as  not  to  endanger  the  oxidation  of  the  sub- 
oxide of  mercury.  If  lead  is  present  the  washing  of  the  subchlo- 
ride must  be  executed  with  special  care  with  water  of  60 — 70°,  till 
the  filtrate  ceases  to  be  colored  with  sulphuretted  hydrogen.  As 
an  additional  security,  it  is  well  to  test  at  last  whether  the  weighed 
subchloride  leaves  no  sulphide  of  lead  behind  on  cautious  ignition 
with  sulphur  in  a stream  of  hydrogen. 

c.  Oxide  and  Suboxide  of  Mercury  from  Oxide  of  Copper, 
Oxide  of  Cadmium,  and  (but  less  well)  from  Oxide  of  Lead. 

If  mercury  is  present  as  oxide  or  as  oxide  and  suboxide,  it  is  106 
precipitated  according  to  § 118,  2,  by  means  of  hydrochloric 
acid  and  phosphorous  acid  as  subchloride.  The  precipitate,  partic- 
ularly when  bismuth  is  present,  is  first  washed  with  water  con- 
taining hydrochloric  acid,  then  with  pure  water,  till  the  washings 


BASES  OF  GROUP  V. 


381 


§ 163.] 


are  no  longer  colored  with  sulphuretted  hydrogen  (H.  Rose*).  In 
the  presence  of  lead,  the  remarks  in  105  must  be  attended  to. 

d.  Chloride  of  Lead  and  Chloride  of  Silver  may  be  sepa-107 
rated  also  by  solution  of  ammonia,  which  dissolves  the  latter,  leav- 
ing the  former  behind  as  basic  chloride  of  lead.  Bear  in  mind  that 
the  chloride  of  silver  must  be  recently  precipitated,  and  with  ex- 
clusion of  light.  The  chloride  of  silver  is  thrown  down  from  the 
ammoniacal  solution  by  nitric  acid.  It  is  necessary  to  test  the 
fluid  filtered  from  the  chloride  of  silver  with  sulphuretted  hydrogen 
to  ascertain  whether  weigh  able  quantities  of  chloride  of  silver  may 
not  be  retained  in  solution  by  the  agency  of  the  ammonia  salts. 

2.  Methods  based  upon  the  Insolubility  of  Sulphate  of  Lead. 

Oxide  of  Lead  from  all  other  Oxides  of  the  Fifth  Group. 

Mix  the  nitric  acid  solution  with  pure  sulphuric  acid  in  not  too  108 
slight  excess,  evaporate  until  the  sulphuric  acid  begins  to  volatilize, 
allow  the  fluid  to  cool,  add  water  (in  which,  if  there  is  a sufficient 
quantity  of  free  sulphuric  acid  present,  the  sulphates  of  mercury 
and  of  bismuth  dissolve  completely),  and  then  filter  the  solution, 
which  contains  the  other  oxides,  without  delay , from  the  undissolved 
sulphate  of  lead.  Wash  the  precipitate  with  water  containing  sul- 
phuric acid,  displace  the  latter  with  spirit  of  wine,  dry,  and  weigh 
(§  116,  3).  Precipitate  the  other  oxides  from  the  filtrate  by  sul- 
phuretted hydrogen.  If  oxide  of  silver  is  present  in  any  notable 
quantity,  this  method  cannot  be  recommended,  as  the  sulphate  of 
silver  is  not  soluble  enough.  In  this  case  you  may  follow  Eliot 
and  Storer,-)*  viz.,  mix  the  solution  with  nitrate  of  ammonia,  warm, 
precipitate  the  greater  portion  of  the  silver  with  chloride  of  ammo- 
nium, evaporate  the  filtrate,  remove  the  ammonia  salts  by  ignition, 
and  in  the  residue  separate  the  small  remainder  of  the  silver  from 
the  lead  with  sulphuric  acid  as  just  directed.  For  the  separation 
of  lead  from  bismuth , on  the  above  principle,  H.  RoseJ  gives  the 
following  process  as  the  best.  If  both  oxides  are  in  dilute  nitric 
acid  solution,  as  is  usually  the  case,  evaporate  to  small  bulk,  and 
add  enough  chloride  of  ammonium  to  dissolve  all  the  teroxide  of 
bismuth ; the  lead  separates  partially  as  chloride.  Should  a por- 
tion of  the  clear  fluid  poured  off  become  turbid  on  the  addition  of 
a drop  of  water,  you  must  add  some  more  hydrochloric  acid,  till  no 
permanent  turbidity  is  produced  unless  several  drops  of  water  are 
added.  The  turbid  fluids  should  all  be  returned,  and  the  glasses 
rinsed  with  alcohol.  Add  now  dilute  sulphuric  acid,  allow  to  stand 
some  time  with  stirring,  add  spirit  of  wine  of  08  sp.  gr.,  stir  well, 
allow  to  settle  for  a long  time,  filter,  wash  the  sulphate  of  lead  first 
with  alcohol,  mixed  with  a small  quantity  of  hydrochloric  acid, 
then  with  pure  alcohol.  Determine  it  after  § 116,  3.  Mix  the  fil- 
trate at  once  with  a large  quantity  of  water,  and  proceed  with 
the  precipitated  basic  chloride  of  bismuth  according  to  § 120,  4 
(p.  234). 

* Pogg.  Anna!  110,  534. 

f Proceedings  of  the  American  Academy  of  Arts  and  Sciences,  Sept.  11,  I860, 
p 52 ; Zeitschrift  f.  Analyt.  Chem.  1,  389. 

X Pogg.  Annal.  110,  432. 


382 


SEPARATION. 


[§  163. 

3.  Different  Deportment  of  the  Oxides  and  Sulphides,  with 
Cyanide  of  Potassium  (Fresenius  and  Haidlen  *). 

a.  Oxide  of  Lead  and  Teroxide  of  Bismuth  from  all  other 
Oxides  of  the  Fifth  Group. 

Mix  the  dilute  solution  with  carbonate  of  soda  in  slight  excess,  add  109 
solution  of  cyanide  of  potassium  (free  from  sulphide  of  potassium), 
heat  gently  for  some  time,  filter,  and  wash.  On  the  filter  you  have 
carbonate  of  lead  and  of  bismuth,  containing  alkali  ; the  filtrate  con- 
tains the  other  metals  as  cyanides  in  combination  with  cyanide  of 
potassium.  The  method  of  effecting  their  further  separation  will 
be  learnt  from  what  follows. 

b.  Oxide  of  Silver  from  Oxide  of  Mercury,  Oxide  of  Copper, 
and  Oxide  of  Cadmium. 

Add  to  the  solution,  which,  if  it  contains  much  free  acid,  must  110 
previously  be  nearly  neutralized  with  soda,  cyanide  of  potassium 
until  the  precipitate  which  forms  at  first  is  redissolved.  The  solu- 
tion contains  the  cyanides  of  the  metals  in  combination  with  cya- 
nide of  potassium  as  soluble  double  salts.  Add  dilute  nitric  acid 
in  excess,  which  effects  the  decomposition  of  the  double  cyanides ; the 
insoluble  cyanide  of  silver  precipitates  permanently,  whilst  the  cya- 
nide of  mercury  remains  in  solution,  and  the  cyanides  of  copper  and 
cadmium  redissolve  in  the  excess  of  nitric  acid.  Treat  the  cyanide 
of  silver  as  directed  § 115,  3,  or  convert  it  into  the  metallic  state 
by  ignition  in  a procelain  crucible  till  the  weight  remains  constant. 

If  the  filtrate  contains  only  mercury  and  cadmium,  precipitate  at 
once  with  sulphuretted  hydrogen,  which  completely  throws  down 
the  sulphides  of  the  two  metals ; but  if  it  contains  copper,  you 
must  first  evaporate  with  sulphuric  acid,  until  the  odor  of  hydro- 
cyanic acid  is  no  longer  perceptible,  and  then  precipitate  with  sul- 
phuretted hydrogen,  or  with  solution  of  potassa  or  soda  (§  119,  3 
or  1). 

c.  Oxide  of  Copper  from  Oxide  of  Silver,  Oxide  of  Mercury, 
and  Oxide  of  Cadmium. 

Mix  the  solution,  as  in  b , with  cyanide  of  potassium  until  HI 
the  precipitate  which  is  first  thrown  down  redissolves ; add  some 
more  cyanide  of  potassium,  then  sulphuretted  hydrogen  water  or 
sulphide  of  ammonium,  as  long  as  a precipitate  forms.  The  sul- 
phides of  silver,  cadmium,  and  mercury  are  completely  thrown 
down,  whilst  the  copper  remains  in  solution,  as  sulphide  dissolved 
in  cyanide  of  potassium.  Allow  the  precipitate  to  subside,  decant 
repeatedly,  treat  the  precipitate,  for  security,  once  more  with  solu- 
tion of  cyanide  of  potassium,  heat  gently,  filter,  and  wash  the  sul- 
phides of  the  metals.  To  determine  the  copper  in  the  filtrate,  evapo- 
rate the  latter,  with  addition  of  nitric  and  sulphuric  acids,  until 
there  is  no  longer  any  odor  of  hydrocyanic  acid  perceptible,  and 
then  precipitate  with  solution  of  potassa  or  soda  (§119,  1),  or  deter- 
mine it  as  subsulphide  (§  119,  3). 

d.  All  the  Metals  of  the  Fifth  Group  from  each  other. 

Mix  the  dilute  solution  with  carbonate  of  soda,  then  with  112 


* Anna!  d.  Chem.  u.  Pharm.  43,  129. 


BASES  OF  GROUP  Y. 


383 


§ 163.] 

cyanide  of  potassium  in  excess,  digest  some  time  at  a gentle  heat, 
and  filter.  On  the  filter  you  have  carbonate  of  lead  and  of  bis- 
muth, containing  alkali  ; separate  the  two  metals  by  a suitable 
method.  Add  to  the  filtrate  dilute  nitric  acid  in  excess,  and  filter 
the  fluid  from  the  precipitated  cyanide  of  silver,  which  determine 
as  directed  § 115,  3.  Neutralize  the  filtrate  with  carbonate  of  soda, 
add  cyanide  of  potassium,  and  pass  sulphuretted  hydrogen  in  ex- 
cess. Add  now  some  more  cyanide  of  potassium,  to  redissolve  the 
sulphide  of  copper  which  may  have  fallen  down,  and  filter  the  fluid, 
which  contains  the  whole  of  the  copper,  from  the  precipitated  sul- 
phide of  mercury  and  sulphide  of  cadmium.  Determine  the  copper 
as  directed  in  c,  and  separate  the  mercury  and  cadmium  as  in  106* 

4.  Formation  and  Separation  of  insoluble  Basic  Salts. 

Teroxide  of  Bismuth-  from  Oxide  of  Copper  and  Oxide  of 

Cadmium  (also  from  the  oxides  of  the  first  four  groups,  with  the  ex- 
ception of  oxide  of  iron). 

Precipitate  the  bismuth  as  basic  chloride  according  to  § 120,  4 (p.  113 
234)  and  throw  down  the  copper  and  cadmium  in  the  filtrate  by  sul- 
phuretted hydrogen.  Results  thoroughly  satisfactory  (H.  Rose  *). 

Teroxide  of  Bismuth  from  Oxide  of  Lead  and  Oxide  of 
Cadmium. 

Separate  the  bismuth  according  to  § 120,  1,  c,  as  basic  nitrate,  and  114 
precipitate  the  lead  and  cadmium  in  the  filtrate  b / sulphuretted  hy- 
drogen. Results  very  satisfactory  (J.  Lowe|). 

Teroxide  of  Bismuth  and  Oxide  of  Copper  from  Oxide  of 
Lead  and  Oxide  of  Cadmium. 

Separate  the  bismuth  after  § 120,  1,  c,  as  basic  nitrate,  then  heat 
the  dish  on  the  water-bath  till  the  neutral  nitrate  of  copper  is  com- 
pletely converted  into  bluish-green  basic  salt  and  no  blue  solution 
is  produced  on  addition  of  water.  Allow  to  cool,  treat  with  an 
aqueous  solution  of  nitrate  of  ammonia  (1  in  500),  filter,  wash  with 
the  same  solution,  and  separate  in  the  solution  lead  from  cadmium ; 
in  the  residue  copper  from  bismuth.  Results  very  satisfactory 
(J.  Lowe,  loc.  cit.). 

5.  Precipitation  of  the  Copper  as  Subsidphocyanide . 

Oxide  of  Copper  from  Oxide  of  Cadmium  [and  the  oxides  of 
Groups  1. — IV.  (Comp.  100*)] 

Precipitate  the  copper  according  to  § 119,  3,  b , as  subsulpho-  115 
cyanide  (Rivot),  and  the  cadmium  from  the  filtrate  as  sulphide.  Re- 
sults good  (H.  Rose). 

6.  Different  Deportment  of  the  Chromates. 

Bismuth  from  Cadmium. 

Precipitate  the  bismuth  as  directed  § 120,  2.  The  filtrate  con-  116 
tains  the  whole  of  the  cadmium.  Concentrate  by  evaporation,  and 
then  precipitate  the  cadmium  by  the  cautious  addition  of  carbonate 
of  soda,  as  directed  § 121,  1,  a (J.  Lowe,J  W.  Pearson||).  The 
results  are  said  to  be  satisfactory. 

* Pogg.  Annal.  110,  430. 

X Joum,  f.  prakt.  Chem.  67,  469. 


f Jouru.  f.  prakt.  Chem.  74,  345. 
| Phil.  Mag.  xi.  204. 


384 


SEPARATION. 


L§  163. 


7.  Different  Deportment  of  the  Sulphides  with  Acids. 

a.  Oxide  of  Mercury  from  Silver,  Bismuth,  Copper,  Cad- 
mium, and  (but  less  well)  from  Lead. 

Boil  the  thoroughly  washed  precipitated  sulphides  with  perfectly  H7 
pure  moderately  dilute  nitric  acid.  The  sulphide  of  mercury  is 
left  undissolved,  the  other  sulphides  are  dissolved.  Absence  of 
chlorine  is  indispensable.  G.  v.  Bath*  employed  this  method, 
which  is  so  universally  used  in  qualitative  analysis,  with  perfect 
success  for  the  separation  of  mercury  from  bismuth. 

b.  Oxide  of  Copper  from  Oxide  of  Cadmium. 

Boil  the  well- washed  precipitates  of  the  sulphides  with  dilute  118 
sulphuric  acid  (1  part  concentrated  acid  and  5 parts  water),  and, 
after  some  time,  filter  the  undissolved  sulphide  of  copper,  to  be  de- 
termined according  to  § 119,  3,  from  the  solution  containing  the 
whole  of  the  cadmium  (A.  W.  Hofmann-)-). 

8.  Volatility  of  some  of  the  Metals , Oxides , Chlorides , or  Sul- 
phides. 

a.  Mercury  from  Silver,  Lead,  Copper  (in  general  from  the  HQ 
metals  forming  non-volatile  chlorides). 


Precipitate  with  sulphuretted  hydrogen,  collect  the  precipitated 
sulphides  on  a weighed  filter,  dry  at  100°,  weigh,  and  mix  uni- 
formly. Introduce  an  aliquot  part  into  the  bulb  D (fig.  68),  [bet- 
ter into  a porcelain  tray  contained  in  a plain  piece  of  Bohemian  com- 
bustion tube  bent  like  D , 0,]  pass  a slow  stream  of  chlorine  gas 
(see  p.  324),  and  apply  a gentle  heat  to  the  bulb,  increasing  this 
gradually  to  faint  redness.  Connect  G during  the  operation  with 


Pogg.  Annal.  96,  322. 


f Annal.  d.  Chem.  u.  Pharm.  115,  286. 


§ 1G3.]  BASES  OF  GROUP  V.  385 

a carboy  containing  moist  hydrate  of  lime.  First  chloride  of  sul- 
phur distils  over,  which  decomposes  with  the  water  in  the  tubes  E 
and  E (p.  325)  ; then  the  chloride  of  mercury  formed  volatilizes,  con- 
densing partly  in  the  receiver^,  partly  in  the  hind  part  of  the  tube 
O.  Cut  off  that  part  of  the  tube,  [or  withdraw  the  tray,]  rinse  the 
sublimate  with  water  into  E , and  mix  the  contents  of  the  latter 
with  the  water  in  F.  Warm  the  solution  until  the  smell  of  chlor- 
ine has  gone  off,  and  then  determine  in  the  fluid  filtered  from  the 
sulphur  which  may  still  remain  undissolved,  the  mercury  as  di- 
rected § 1 1 8.  If  the  residue  consists  of  chloride  of  silver  alone,  or 
chloride  of  lead  alone,  you  may  weigh  it  at  once ; but  if  it  contains 
several  metals,  you  must  reduce  the  chlorides  by  ignition  in  a stream 
of  hydrogen  gas,  and  dissolve  the  reduced  metals  in  nitric  acid,  for 
their  ulterior  separation.  Bear  in  mind  that,  in  presence  of  lead, 
the  sulphides  and  the  chlorides  must  be  heated  gently , in  the 
chlorine  and  hydrogen  respectively,  otherwise  some  chloride  of  lead 
might  volatilize. 

If  it  is  intended  to  determine  the  mercury  by  the  difference,,  in- 
stead of  in  the  direct  way,  the  apparatus  may  be  much  simplified. 

In  this  case,  however,  great  care  must  be  bestowed  on  the  drying  of 
the  sulphides  at  100°,  because,  for  instance,  the  sulphide  of  lead 
on  drying  first  becomes  lighter  from  loss  of  moisture,  then  gradually 
heavier  again  by  absorption  of  oxygen.  Hence  the  method  should 
only  be  adopted  when  a small  quantity  only  of  another  metal  is 
present  with  the  mercury.  Weigh  the  dried  precipitate  every  half 
hour,  and  take  the  lowest  weight  as  the  correct  one.  Then  ignite 
an  aliquot  part  of  the  precipitate  in  the  stream  of  hydrogen  in  a 
crucible  with  perforated  cover,  or  in  a tube  with  porcelain  tray. 

The  method  cannot  be  applied  unless  only  one  metal  is  present  with 
the  mercury.  From  the  residue  in  the  crucible  or  boat  reckon  how 
much  the  whole  precipitate,  dried  at  100°,  would  have  yielded, 
then  calculate  the  result  into  sulphide,  in  which  form  the  substance 
was  contained  in  the  dried  precipitate — the  difference  is  sulphide 
of  mercuryr. 

By  ignition  in  hydrogen  sulphide  of  silver  yields  the  metal,  sul- 
phide of  copper  yields  the  subsulphide,  sulphide  of  lead  remains  un- 
altered. Results  good. 

In  alloys  or  mixtures  of  oxides  the  mercury  may  usually  be  de- 
termined with  simplicity  from  the  loss  on  ignition. 

6.  Teroxide  of  Bismuth  from  Oxide  of  Silver,  Oxide  of 
Lead,  and  Oxide  of  Copper. 

The  separation  is  effected  exactly  in  the  same  way  as  that  of  mer- 120 
cury  from  the  same  metals  (119).  The  method  is  more  especially 
convenient  for  the  separation  of  the  metals  in  alloys.  Care  must 
be  taken  not  to  heat  too  strongly,  as  otherwise  chloride  of  lead 
might  volatilize  ; nor  to  discontinue  the  application  of  heat  too  soon, 
as  otherwise  bismuth  would  remain  in  the  residue.  Put  water  con- 
taining hydrochloric,  acid  in  the  tubes  E and  jP(fig.  68),  and  de- 
termine the  bismuth'therein  according  to  § 120. 

9.  Precipitation  of  one  Metal  by  another  in  the  Metallic  State. 

Oxide  of  Lead  from  Teroxide  of  Bismuth. 

Precipitate  the  solution  with  carbonate  of  ammonia,  wash  the  121 

25 


386 


SEPARATION. 


[§163. 

precipitated  carbonates,  and  dissolve  in  acetic  acid,  in  a flask  ; place 
a weighed  rod  of  pure  lead  upright  in  the  solution  and  nearly  fill 
up  with  water,  so  that  the  rod  may  be  entirely  covered  by  the  fluid ; 
close  the  flask,  and  let  it  stand  for  about  12  hours,  with  occasional 
shaking.  Wash  the  precipitated  bismuth  oft'  from  the  lead  rod, 
collect  on  a filter,  wash,  and  dissolve  in  nitric  acid  ; evaporate  the 
solution,  and  determine  the  bismuth  as  directed  § 120.  Determine 
the  lead  in  the  filtrate  as  directed  § 116.  Dry  the  leaden  rod,  and 
weigh  ; subtract  the  loss  of  weight  which  the  rod  has  suffered  in 
the  process,  from  the  amount  of  the  lead  obtained  from  the  filtrate 
(Ullgren). 

10.  Separation  of  Silver  by  Cupellation. 

Cupellation  was  formerly  the  universal  method  of  determining  122 
silver  in  alloys  with  copper,  lead,  &c.  The  alloy  is  fused  to- 
gether with  a sufficient  quantity  of  pure  lead  to  give  to  1 part  of  sil- 
ver 16  to  20  parts  of  lead,  and  the  fused  mass  is  heated,  in  a muffle, 
in  a small  cupel  made  of  compressed  bone-ash.  Lead  and  copper 
are  oxidized,  and  the  oxides  absorbed  by  the  cupel,  the  silver  being 
left  behind  in  a state  of  purity.  One  part  by  weight  of  the  cupel 
absorbs  the  oxide  of  about  2 parts  of  lead  ; the  quantity  of  the  sam- 
ple to  be  used  in  the  experiment  may  be  estimated  accordingly. 

This  method  is  one  of  the  safest  processes  to  determine  very  small 
quantities  of  silver  in  alloys.*  With  regard  to  details,  I refer  to 
the  “ Silver  Assay,”  § 226. 

11.  Volumetric  Determination  of  Silver  in  Presence  of  Lead 
and  Copper . 

See  § 115,  5,  II.  (p.  215).  123 

1 

12.  Methods  based  on  the  behavior  of  Ammoniacal  Solutions 
of  Subchloride  of  Copper  and  of  Oxide  of  Silver  with 
each  other. 

If  you  pour  a solution  of  ammonio-subchloride  of  copper,  contain- 
ing large  excess  of  ammonia,  into  a solution  of  nitrate  of  silver  like- 
wise supersaturated  with  ammonia,  a precipitate  of  metallic  silver 
is  immediately  formed. 

On  this  reaction  Millon  and  CoMMAiLLEf  base  the  following 
methods  of  separation  : — 

a.  Determination  of  Oxide  of  Silver  in  presence  of  Oxide 
of  Lead  and  Oxide  of  Copper. 

Mix  with  ammonia  in  excess,  filter,  add  excess  of  ammonio-sub-  124 
chloride  of  copper,  allow  the  precipitate  to  subside,  filter  it  off,  wash 
with  ammoniacal  water,  ignite,  and  weigh.  The  test-analyses  that 
have  been  adduced  are  perfectly  satisfactory.  Very  small  quanti- 
ties of  the  precipitated  metallic  silver  I should  prefer  to  dissolve  in 
nitric  acid,  evaporating  to  dryness,  and  determining  the  silver  after 
Pisani’s  method  (p.  215). 

b.  Determination  of  Suboxide  of  Copper  in  the  presence 

of  the  Oxide.  * 


* Compare  Malaguti  and  Durocher,  Compt.  rend.  29,  689;  Dingier,  115,  276. 
f Compt.  rend.  56,  309;  Zeitschrift  f.  analyt.  Chem.  2,  212. 


BASES  OF  GROUP  VI. 


387 


§ 164.] 

Dissolve  the  compound  in  hydrochloric  acid,  add  excess  of  am-  125 
inonia,  then  excess  of  solution  of  nitrate  of  silver,  which  has  been 
mixed  with  so  much  ammonia  that  no  separation  of  chloride  of  sil- 
ver can  take  place.  All  these  operations  must  be  performed  in  an 
apparatus  through  which  hydrogen  (washed  with  ammoniacal  silver 
solution)  is  passing.  The  precipitated  silver  is  finally  determined 
as  in  124.  1 eq.  of  the  same  corresponds  to  1 eq.  Cu2  O or  Cu2  Cl. 

The  total  amount  of  the  copper  is  best  determined  in  another  por- 
tion of  the  substance. 


SIXTH  GROUP. 


TEROXIDE  OF  GOLD BINOXIDE  OF  PLATINUM PROTOXIDE  OF  TIN 

BINOXIDE  OF  TIN TEROXIDE  OF  ANTIMONY (ANTIMONIC  ACID) 

ARSENIOUS  ACID ARSENIC  ACID. 

I.  Separation  of  the  Oxides  of  the  Sixth  Group  from 
the  Oxides  of  the  first  Five  Groups. 

§ 164. 

Index : — The  Nos.  refer  to  those  in  the  margin. 

Gold,  from  the  oxides  of  Groups  I. — III.,  126,  131. 

“ IV.,  126,  129,  131. 

44  silver,  129,  146. 

44  mercury,  129,  131,  141. 

“ lead,  129,  150. 

“ copper,  129,  131. 

“ bismuth,  129,  131,  150. 

“ cadmium,  129,  131. 

Platinum  from  the  oxides  of  Groups  I. — III. , 126. 

“ “ IV.,  126,  130,  132. 

“ silver,  130. 

44  mercury,  130,  132. 

“ lead,  130. 

44  copper,  130,  132. 

44  bismuth,  130,  132. 

“ cadmium,  130,  132. 

Tin  from  the  oxides  of  Groups  I.  and  II.,  126,  134,  140. 

“ “ III.,  126,  134. 

“ zinc,  126,  128,  133,  134. 

44  manganese,  126,  128,  134. 

44  nickel  and  cobalt,  126,  128,  133,  134,  139. 

“ iron,  126,  128. 

44  silver,  127,  128.  133,  139. 

44  mercury,  127,  128,  133. 

“ lead,  127,  128,  133,  139. 

44  copper,  127,  128,  133,  134,  139. 

“ bismuth,  127,  128. 

“ cadmium,  127,  128,  133. 

Antimony  from  the  oxides  of  Groups  I.  and  II. , 126,  140. 

“ “ III.,  126. 

“ zinc,  126,  128. 

44  manganese,  126,  128. 

44  nickel  and  cobalt,  126,  128,  138,  139. 

“ iron,  126,  128,  137. 

44  silver,  127,  128,  139. 

44  mercury,  127,  128,  135,  147. 

44  lead,  127,  128,  139,  149. 

44  copper,  127,  128,  137. 

44  bismuth,  127,  128. 

44  cadmium,  127,  128. 


388 


SEPARATION. 


[§  164. 


Arsenic  from  oxides  of  Group  I.,  126,  140,  144, 145. 

“ “ II.,  126,  136,  140, 144, 145,  148. 

“ “ III.,  126,  143,  144. 

“ zinc,  126,  128,  136,  142,  144,  145. 

“ manganese,  126,  128,  136.  142,  143,  144,  145. 

“ nickel  and  cobalt,  126,  128, 136,  138, 139,  142, 

143.  144,  145. 

“ iron,  126,  128,  136,  137,  142,  143,  144. 

“ silver,  127,  128,  136,  139,  144. 

“ mercury,  127,  128,  136,  144,  147. 

“ lead,  127,  128,  136,  139,  142,  144,  148. 

“ copper,  127,  128,  136,  137,  139,  142,  143,  144. 

“ bismuth,  127,  128,  136,  144. 

“ cadmium,  127,  128,  136,  143,  144. 

A.  General  Methods. 

1 . Method  based  upon  the  Precipitation  of  the  Oxides  of  the 

Sixth  Group  from  Acid  Solutions  by  Sulphuretted  Hydrogen. 

All  Oxides  of  the  Sixth  Group  from  those  of  the  first 
Four  Groups. 

Conduct  into  the  acid  * solution  sulphuretted  hydrogen  in  excess,  126 
and  filter  off  the  precipitated  sulphides  (corresponding  to  the  oxides 
of  the  sixth  group). 

The  points  mentioned  95,  «,  /?,  and  y must  also  be  attended  to 
here.  As  regards  y,  antimony  and  tin  are  to  be  inserted  between 
cadmium  and  mercury,  in  the  order  of  metals  there  given.  With 
respect  to  the  particular  conditions  required  to  secure  the  proper 
precipitation  of  certain  metals  of  the  sixth  group,  I refer  to  Section 
IV.  I have  to  remark  in  addition : — 

a , That  sulphuretted  hydrogen  fails  to  separate  arsenic  acid  from 
oxide  of  zinc,  as,  even  in  presence  of  a large  excess  of  acid,  the 
whole  or  at  least  a portion  of  the  zinc  precipitates  with  the  arsenic 
as  Zn  S,  As  S5  (Wohler).  To  secure  the  separation  of  the  two 
bodies  in  a solution,  the  arsenic  acid  must  first  be  converted  into 
arsenious  acid,  by  heating  with  sulphurous  acid,  before  the  sulphu- 
retted hydrogen  is  conducted  into  the  fluid. 

/3.  That  in  presence  of  antimony,  tartaric  acid  should  be  added, 
as  otherwise  the  sulphide  of  antimony  will  contain  chloride. 

2.  Method  based  upon  the  Solubility  of  the  Sulphides  of  Metals 

of  the  Sixth  Group  in  Sulphides  of  the  Alkali  Metals, 
a.  The  Oxides  of  Group  VI.  (with  the  exception  of  Gold  and  127 
Platinum)  from  those  of  Group  V. 

Precipitate  the  acid  solution  with  sulphuretted  hydrogen,  paying 
due  attention  to  the  directions  given  in  Section  IV.  under  the 
heads  of  the  several  metals,  and  also  to  the  remarks  in  126.  The 
precipitate  consists  of  the  sulphides  of  the  metals  of  Groups  V. 
and  VI.  Wash,  treat  immediately  after  with  yellow  sulphide  of  am- 
monium in  excess,  and  digest  the  mixture  for  some  time  at  a gen- 
tle heat ; filter  off  the  clear  fluid,  treat  the  residue  again  with  sul- 
phide of  ammonium,  digest  a short  time,  repeat  the  same  operation, 
if  necessary,  a third  and  fourth  time,  filter,  and  wash  the  residuary 
sulphides  of  Group  V.  with  water  containing  sulphide  of  ammo- 
nium. If  protosulphide  of  tin  is  present,  some  flowers  of  sulphur 


Hydrochloric  acid  answers  best  as  acidifying  agent. 


§ 104.] 


OXIDES  OF  GROUP  VI. 


389 


must  be  added  to  the  sulphide  of  ammonium,  unless  the  latter  be 
very  yellow.  In  presence  of  cqpper,  the  sulphide  of  which  is  a lit- 
tle soluble  in  [merely  warm]  sulphide  of  ammonium,  [boil  a short 
time  or]  use  sulphide  of  sodium  instead.  However,  this  substitu- 
tion can  be  made  only  in  the  absence  of  mercury,  since  the  sulphides 
of  that  metal  are  soluble  in  sulphide  of  sodium. 

Add  to  the  alkaline  filtrate,  gradually,  hydrochloric  acid  in  small 
portions,  until  the  acid  predominates;  allow  to  subside,  and  then 
filter  off  the  sulphides  of  the  metals  of  the  sixth  group,  which  are 
mixed  with  sulphur. 

Schneider*  states  that  he  failed  in  effecting  complete  separation 
of  bisulphide  of  bismuth  from  bisulphide  of  tin  by  digestion  with 
sulphide  of  potassium,  but  succeeded  in  accomplishing  that  object 
by  conducting  sulphuretted  hydrogen  into  the  potassa  solution  of 
tartrate  of  teroxide  of  bismuth  and  protoxide  of  tin  (which  decom- 
pose into  binoxide  of  bismuth  and  binoxide  of  tin). 

If  a solution  contains  much  arsenic  acid  in  presence  of  small 
quantities  of  copper,  bismuth,  &c.,  it  is  convenient  to  precipitate 
these  metals  (together  with  a very  small  amount  of  sulphide  of 
arsenic)  by  a brief  treatment  with  sulphuretted  hydrogen.  Filter, 
extract  the  precipitate  with  sulphide  of  ammonium  (or  sulphide  of 
potassium),  acidify  the  solution  obtained,  mix  it  with  the  former 
filtrate  containing  the  principal  quantity  of  the  arsenic,  and  pro- 
ceed to  treat  further  with  sulphuretted  hydrogen. 

b.  The  Oxides  of  Group  VI.  (with  the  exception  of  Gold  and  128 
Platinum)  from  those  of  Groups  IV.  and  V. 

a.  Neutralize  the  solution  with  ammonia,  add  chloride  of  ammo- 
nium, if  necessary,  and  then  yellow  sulphide  of  ammonium  in  ex- 
cess ; digest  in  a closed  flask,  for  some  time  at  a moderate  heat,  and 
then  proceed  as  in  127-  Repeated  digestion  with  fresh  quantities 
of  sulphide  of  ammonium  is  indispensable.  On  the  filter,  you  have 
the  sulphides  of  the  metals  of  Groups  IV.  and  V.  Wash  with 
water  containing  sulphide  of  ammonium. 

In  presence  of  nickel,  this  method  offers  peculiar  difficulties; 
traces  of  sulphide  of  mercury,  too,  are  liable  to  pass  into  the  fil- 
trate. In  presence  of  copper  (and  absence  of  mercury),  soda  and 
sulphide  of  sodium  are  substituted  for  ammonia  and  sulphide  of 
ammonium. f 

/?.  In  the  analysis  of  solid  compounds  (oxides  or  salts),  it  is  in 
most  cases  preferable  to  fuse  the  substance  with  3 parts  of  dry  car- 
bonate of  soda  and  3 of  sulphur,  in  a covered  porcelain  crucible, 
over  a lamp.  When  the  contents  are  completely  fused,  and  the  ex- 
cess of  sulphur  is  volatilized,  the  mass  is  allowed  to  cool,  and  then 

* Annal.  d.  Cliem.  u.  Pharm.  101,  64. 

I The  accuracy  of  this  method  has  been  called  in  question  by  Bloxam  (Quart. 
Jour.  Chem.  Soc.  5, 119).  That  chemist  found  that  sulphide  of  ammonium  fails 
to  separate  small  quantities  of  bisulphide  of  tin  from  large  quantities  of  sul- 
phide of  mercury  or  sulphide  of  cadmium  (1  : 100) ; and  that  more  especially 
the  separation  of  copper  from  tin  and  antimony  (also  from  arsenic)  by  this 
method  is  a failure,  as  nearly  the  whole  of  the  tin  remains  with  the  copper.  The 
latter  statement  I cannot  confirm,  for  Mr.  Lucius,  in  my  laboratory,  has  suc- 
ceeded in  separating  copper  from  tin  by  means  of  yellowish  sulphide  of  sodium 
completely  ; but  it  is  indispensable  to  digest  three  or  four  times  with  sufficiently 
large  quantities  of  the  solvent,  as  stated  in  the  text. 


300 


SEPARATION. 


L§  1^4. 


treated  with  water,  which  dissolves  the  snlphosalts  of  the  metals  of 
the  sixth  group,  leaving  the  sulphides  of  Groups  IV.  and  Y.  undis- 
solved. By  this  means,  even  ignited  binoxide  of  tin  may  be  readily 
tested  for  iron,  &c.,  and  the  amount  of  the  admixture  determined 
(H.  Bose).  The  solution  of  the  sulphosalts  is  treated  as  in  127. 
In  the  presence  of  copper,  traces  of  the  sulphide  may  be  dissolved 
with  the  sulphides  of  Group  YI.  Occasionally  a little  sulphide  of 
iron  dissolves,  coloring  the  solution  green.  In  that  case  add  some 
chloride  of  ammonium,  and  digest  till  the  solution  has  turned  yellow. 

B.  Special  Methods. 

1.  Insolubility  of  some  Metals  of  the  Sixth  Group  in  Acids, 
a.  Gold  from  Metals  of  Groups  IY.  and  Y.  in  Alloys. 


a.  Boil  the  alloy  with  pure  nitric  acid  (not  too  concentrated),  or,  129 
according  to  circumstances,  with  hydrochloric  acid.  The  other 
metals  dissolve,  the  gold  is  left.  The  alloy  must  be  reduced  to  fil- 
ings, or  rolled  out  into  a thin  sheet.  If  the  alloy  were  treated  with 
concentrated  nitric  acid,  and  at  a temperature  below  boiling,  a little 
gold  might  dissolve  in  consequence  of  the  co-operation  of  nitrous 
acid.  In  the  presence  of  silver  and  lead,  this  method  is  only  appli- 
cable when  they  amount  to  more  than  80  per  cent.,  since  otherwise 
they  are  not  completely  dissolved.  Alloys  of  silver  and  gold  con- 
taining less  than  80  per  cent,  of  silver  are  therefore  fused  together 
with  3 parts  of  lead,  before  they  are  treated  with  nitric  acid.  The 
residuary  gold  is  weighed;  but  its  purity  must  be  ascertained,  by 
dissolving  in  cold  dilute  nitrohydrochloric  acid,  not  in  concentrated 
hot  acid,  as  chloride  of  silver  also  is  soluble  in  the  latter. 

At  the  Mint  Conference  held  at  Yienna  in  1857,  the  following 
process  was  agreed  upon  for  the  mints  in  the  several  states  of  Ger- 
many. Add  to  1 part  of  gold,  supposed  to  be  present,  2J  parts  of 
pure  silver ; wrap  both  the  alloy  and  the  silver  in  paper  together, 
and  introduce  into  a cupel  in  which  the  requisite  amount  of  lead 
is  just  fusing.*  After  the  removal  of  the  lead  (by  absorption),  the 
button  of  gold  and  silver  is  flattened,  by  hammering  or  rolling,  then 
ignited,  and  rolled  ; the  rolls  are  treated  first  with  nitric  acid  of 
1*2  sp.  gr.,  afterwards  with  nitric  acid  of  1*3  sp.  gr.,  rinsed,  ignited, 
and  weighed,  f 

|3.  Heat  the  alloy  (previously  filed  or  rolled)  in  a capacious  pla- 
tinum dish  with  a mixture  of  2 parts  pure  concentrated  sulphuric 
acid  and  1 part  water,  until  the  evolution  of  gas  has  ceased,  and  the 
sulphuric  acid  begins  to  volatilize ; or  fuse  the  alloy  with  bisul- 
phate of  potassa  (H.  Rose).  Separate  the  gold  from  the  sulphates 
of  the  other  metals,  by  treating  the  mass  first  with  cold,  finally  with 
boiling  water.  It  is  advisable  to  repeat  the  operation  with  the 
separated  gold,  and  ultimately  test  the  purity  of  the  latter. 

y.  The  methods  given  in  a and  j 3 may  be  united,  i.e.,  the  cu- 
pelled and  thinly-rolled  metal  may  be  first  warmed  with  nitric  acid 


* If  the  weighed  sample,  say  0 25  grm  , contains  98-92£  gold,  3 grin,  of  lead 
are  required  ; if  92-87 '5,  4 grm.  ; if  87 '5-75,  5 grm.  ; if  75-60,  6 grm.  ; if  60-35, 
7 grm.  ; if  less  than  35,  8 grm. 

f Kunst-  und  G-ewerbeblatt  f.  Baiern,  1857.  151 ; Chem.  Centralbl.  1857,  307 ; 
V !yt  Centralbl.  1857,  1151,  1471,  1639. 


OXIDES  OF  GROUP  VI. 


391 


1 G 4. 


of  1*2  sp.  gr.,  then  thoroughly  washed,  the  gold  boiled  5 minutes 
with  concentrated  sulphuric  acid,  washed  again,  and  ignited  (Mas- 
CAZZINI,  BuGATTl). 

b.  Platinum  from  Metals  of  Groups  XV.  and  V.,  in  Alloys. 

The  separation  is  effected  by  treating  with  sulphuric  acid,  or,  bet- 130 
ter  still,  with  bisulphate  of  potassa  (129>  0)  j but  not  with  nitric 
acid,  as  platinum  in  alloys  will,  under  certain  circumstances,  dis- 
solve in  that  acid. 

2.  Separation  of  Gold  in  the  metallic  state. 

Gold  from  all  Oxides  of  Groups  X. — V.,  with  the  exception 
of  Oxide  of  Lead  and  Oxide  of  Silver. 

Precipitate  the  hydrochloric  acid  solution  with  oxalic  acid  as  di-  131 
rected  § 123,  5,  y,  or  with  sulphate  of  iron,  § 123,  5,  a,  and  filter 
off  the  gold  when  it  has  completely  separated.  Take  care  to  add  a 
sufficient  quantity  of  hydrochloric  acid  to  prevent  oxalates  insolu- 
ble in  water  precipitating  along  with  the  gold,  for  want  of  a solvent. 

3.  Precipitation  of  Platinum  as  Poiassio - or  Ammonio-bichlo  - 

ride  of  Platinum. 

Platinum  from  the  Oxides  of  Groups  IV.  and  V.,  with  the 
exception  of  Lead  and  Silver. 

Precipitate  the  platinum  with  chloride  of  potassium  or  chloride  132 
of  ammonium  as  directed  § 124,  and  wash  the  precipitate  thoroughly 
with  spirit  of  wine.  The  platinum  prepared  from  the  precipitated 
ammonium  or  potassium  salt  is  to  be  tested  after  being  weighed,  to 
see  whether  it  yields  any  metal  (especially  iron)  to  fusing  bisul- 
phate of  potassa. 

4.  Separation  of  Oxides  insoluble  in  Nitric  Acid. 

a.  Tin  from  Metals  of  Groups  IV.  and  V.  (not  from  Bismuth, 
Iron,  or  Manganese*)  in  Alloys. 

Treat  the  finely  divided  alloy,  or  the  metallic  powder  obtained  133 
by  reducing  the  oxides  in  a stream  of  hydrogen  with  nitric  acid,  as 
directed  § 126,  1,  a.  The  filtrate  contains  the  other  metals  as 
nitrates.  As  binoxide  of  tin  is  liable  to  retain  traces  of  copper 
and  lead,  you  must,  in  an  accurate  analysis,  test  an  aliquot  part  of 
it  for  these  bodies,  and  determine  their  amount  as  directed  118,& 

Brunner  recommends  the  following  course  of  proceeding,  by 
which  the  presence  of  copper  in  the  tin  may  be  effectually  guarded 
against.  Dissolve  the  alloy  in  a mixture  of  1 part  of  nitric  acid, 

4 parts  of  hydrochloric  acid,  and  5 parts  of  water ; dilute  the  solu- 
tion largely  with  water,  and  heat  gently.  Add  crystals  of  carbon- 
ate of  soda  until  a distinct  precipitate  has  formed,  and  boil.  (In 
presence  of  copper,  the  precipitate  must,  in  this  operation,  change 
from  its  original  bluish-green  to  a brown  or  black  tint.)  When 
the  fluid  has  been  in  ebullition  some  10  or  15  minutes,  allow  it  to 
cool,  and  then  add  nitric  acid,  drop  by  drop,  until  the  reaction  is 

* If  the  alloy  of  tin  contains  bismuth  or  manganese,  there  remains  with  the 
binoxide  of  tin  always  teroxide  of  bismuth  or  sesquioxide  of  manganese,  which 
cannot  be  extracted  by  nitric  acid  ; if  it  contains  iron,  on  the  contrary,  some 
binoxide  of  tin  always  dissolves  with  the  iron,  and  cannot  be  separated  even  by 
repeated  evaporation(H  Rose,  Pogg.  Anna!,  cxii.  169,  170,  172). 


392 


SEPARATION. 


distinctly  acid ; digest  the  precipitate  for  several  hours,  when  it 
should  have  acquired  a pure  white  color.  The  binoxide  of  tin 
thus  obtained  is  free  from  copper ; but  it  may  contain  some  iron, 
which  can  be  removed  as  directed  in  128,  0. 

Before  the  binoxide  of  tin  can  be  considered  pure,  it  must  be 
tested  also  for  silicic  acid,  as  it  frequently  retains  traces  of  this  sub- 
stance. To  this  end,  an  aliquot  part  is  fused  with  3 — 4 parts  of  car- 
bonate of  soda  and  potassa,  the  fused  mass  boiled  with  water,  and  the 
solution  filtered ; hydrochloric  acid  is  then  added  to  the  filtrate, 
and,  should  silicic  acid  separate,  the  fluid  is  filtered  oft'  from  this 
substance.  The  tin  is  then  precipitated  by  sulphuretted  hydrogen, 
and  the  silicic  acid  still  remaining  in  the  filtrate  is  determined  in  the 
usual  way  (§140).  If  hydrochloric  acid  has  produced  a precipitate  of 
silicic  acid,  the  last  filtration  is  effected  on  the  same  filter  (Khittel*)  . 

b.  Antimony  from  the  Metals  of  Groups  IY.  and  Y.  in 
Alloys. 

Proceed  as  in  «,  filter  off  the  precipitate,  and  convert  it  by  igni- 
tion into  antimoniate  of  teroxide  of  antimony  (§  125,  2).  Results 
only  approximative,  as  a little  teroxide  of  antimony  dissolves. 
Alloys  of  antimony  and  lead,  containing  the  former  metal  in  ex- 
cess, should  be  previously  fused  with  a weighed  quantity  of  pure 
lead  (Yarrentrapp|).  [See  Tookey,  Journ.  Chem.  Soc.  xv.  464.] 

5.  Precipitation  of  P inoxide  of  Tin  by  Neutral  Salts  (e.  g.. 
Sulphate  of  Soda ) or  by  Sulphuric  Acid. 

Tin  from  the  Oxides  of  Groups  I.,  II.,  III. ; also  from  Pro- 
toxide of  Manganese,  Oxide  of  Zinc,  Protoxides  of  Nickel 
and  Cobalt,  Oxide  of  Copper  (Teroxide  of  Gold). 

Precipitate  the  hydrochloric  acid  solution,  which  must  contain  134 
the  tin  entirely  as  binoxide  (bichloride),  according  to  § 126,  1,  5, 
by  nitrate  of  ammonia  or  sulphate  of  soda  (Lowenthal),  or  by  sul- 
phuric acid,  which,  H.  Bose  says,  answers  equally  well.  Alloys 
are  treated  as  follows : — First,  oxidize  by  digestion  with  nitric  acid  ; 
when  no  more  action  takes  place,  evaporate  the  greater  portion  of 
the  nitric  acid  in  a porcelain  dish,  moisten  the  mass  with  strong 
hydrochloric  acid,  and  after  half  an  hour  add  water,  in  which  the 
metachloride  of  tin  and  the  other  chlorides  dissolve.  Alloys  of  tin 
and  gold  are  dissolved  in  aqua  regia,  the  excess  of  acid  evaporated, 
and  the  solution  diluted  with  much  water,  before  precipitating 
with  sulphuric  acid. 

It  must  be  remembered  that  in  this  process  any  phosphoric  acid 
that  may  be  present  is  precipitated  entirely  or  partially  with  the 
binoxide  of  tin.  After  the  precipitate  has  been  well  washed  by 
decantation,  Lowenthal  recommends  to  boil  with  a mixture  of  1 
part  nitric  acid  (sp.  gr.  P2)  and  9 parts  water,  then  to  transfer 
to  the  filter,  and  wash  thoroughly.  Results  very  satisfactory.  If 
the  fluid  contains  sesquioxide  of  iron,  a portion  of  the  latter  always 
falls  down  with  the  tin.  Hence  the  binoxide  of  tin  must  be  tested 
for  iron  according  to  128,  0,  and  if  present,  its  amount  must  be 
determined  and  deducted. 


* Chem.  Centralbl.  1857,  929. 


f Dingler’s  polyt.  Journ.  158,  316. 


OXIDES  OF  GROUP  VI. 


393 


§ 164.] 

6.  Insolubility  of  Sulphide  of  Mercury  in  Hydrochloric  Acid. 

Mercury  from  Antimony. 

Digest  the  precipitated  sulphides  with  moderately  strong  hydro- 135 
chloric  acid  in  a distilling  apparatus.  The  sulphide  of  antimony  dis- 
solves, while  the  sulphide  of  mercury  remains  behind.  Expel  all 
the  hydrosulphuric  acid,  then  add  tartaric  acid,  dilute,  filter,  mix  the 
filtrate  with  the  distillate  which  contains  a little  antimony,  and  pre- 
cipitate with  sulphuretted  hydrogen.  The  sulphide  of  mercury  may 
be  weighed  as  such  (F.  Field*). 

7.  Conversion  of  Arsenic  and  Antimony  into  Alkaline  Arse- 

niate  and  Antimoniate. 

a.  Arsenic  from  the  Metals  and  Oxides  of  Groups  II.,  IY., 
and  Y. 

If  you  have  to  do  with  arsenites  or  arseniates,  fuse  with  3 parts  136 
of  carbonate  of  soda  and  potassa  and  1 part  of  nitrate  of  potassa ; 
if  an  alloy  has  to  be  analyzed  it  is  fused  with  3 parts  of  carbonate 
of  soda  and  3 parts  of  nitrate  of  potassa.  In  either  case  the  residue 
is  boiled  with  water,  and  the  solution,  which  contains  the  arseniates 
of  the  alkalies,  filtered  from  the  undissolved  oxides  or  carbonates. 

The  arsenic  acid  is  determined  in  the  filtrate  as  directed  § 127,  2.  If 
the  quantity  of  arsenic  is  only  small,  the  fusion  may  be  effected  in  a 
platinum  crucible ; but  if  more  considerable,  the  process  must  be 
conducted  in  a porcelain  crucible,  as  platinum  would  be  injuriously 
affected  by  it.  In  the  latter  case,  bear  in  mind  that  the  fused  mass 
is  contaminated  with  silicic  acid  and  alumina.  If  the  alloy  contains 
much  arsenic  a small  quantity  may  be  readily  lost  by  volatilization, 
even  though  the  operation  be  cautiously  conducted.  In  such  a case, 
therefore,  it  is  better  first  to  oxidize  with  nitric  acid,  then  to  evapo- 
rate, and  to  fuse  the  residue  as  above  directed  with  carbonate  of  soda 
and  nitrate  of  potassa. 

b.  Arsenic  and  Antimony  from  Copper  and  Iron,  especially 
in  ores  containing  sulphur. 

Diffuse  the  very  finely  pulverized  mineral  through  pure  solution  137 
of  potassa,  and  conduct  chlorine  into  the  fluid  (comp.  p.  327,  A , b). 

The  iron  and  copper  separate  as  oxides,  the  solution  contains  sulphate, 
arseniate,  and  antimoniate  of  potassa  (Rivot,  Beudant,  and  DAGUiNf). 

c.  Arsenic  and  Antimony  from  Cobalt  and  Nickel. 

Dilute  the  nitric  acid  solution  with  water,  add  a large  excess  of  138 
potassa,  heat  gently,  and  conduct  chlorine  into  the  fluid  until  the  pre- 
cipitate is  black.  The  solution  contains  the  whole  of  the  arsenic  and 
antimony,  the  precipitate  the  nickel  and  cobalt,  in  form  of  sesqui- 
oxide  (Rivot,  Beudant,  and  Daguin,  loc.  cit.) 

8.  Volatility  of  certain  Chlorides  or  Metals. 

a.  Tin,  Antimony,  Arsenic  from  Copper,  Silver,  Lead, 
Cobalt,  Nickel. 

Treat  the  sulphides  with  a stream  of  chlorine,  proceeding  exactly  139 

* Quart.  Joum.  Chem.  Soc.  12,  32. 

f Compt.  rend.  1853,  835;  Joum.  f.  prakt.  Chem.  61,  133. 


394 


SEPARATION. 


[§  164. 


as  directed  in  119-  In  presence  of  antimony,  fill  the  tubes  E and 
F (fig.  68)  with  a solution  of  tartaric  acid  in  water,  mixed  with 
hydrochloric  acid.  The  metals  may  be  also  separated  by  this  method 
in  alloys.  The  alloy  must  be  very  finely  divided.  Arsenical  alloys 
are  only  very  slowly  decomposed  in  this  way.  If  tin  and  copper  are 
separated  in  this  manner,  according  to  the  experience  of  H.  Rose,*  a 
small  trace  of  tin  remains  with  the  chloride  of  copper.  [See  Tookey, 
Journ.  Chem.  Soc.  xv.,  466.] 

b.  Binoxide  of  Tin,  Teroxide  of  Antimony  (and  also  Anti- 
monic  Acid),  Arsenious,  and  Arsenic  Acids,  from  Alkalies 
and  Alkaline  Earths. 

Mix  the  solid  compound  with  5 parts  of  pure  chloride  of  am- 140 
monium  in  powder,  in  a porcelain  crucible,  cover  this  with  a concave 
platinum  lid,  on  which  some  chloride  of  ammonium  is  sprinkled,  and 
ignite  gently  until  all  chloride  of  ammonium  is  driven  off;  mix  the 
contents  of  the  crucible  with  a fresh  portion  of  that  salt,  and  repeat 
the  operation  until  the  weight  remains  constant.  In  this  process,  the 
chlorides  of  tin,  antimony,  and  arsenic,  escape,  leaving  the  chlorides 
of  the  alkaline  and  alkaline  earthy  metals.  The  decomposition  pro- 
ceeds most  rapidly  with  alkaline  salts.  With  regard  to  alkaline 
earthy  salts  it  is  to  be  observed  that  those  which  contain  antimonic 
acid  or  binoxide  of  tin  are  generally  decomposed  completely  by  a 
double  ignition  with  chloride  of  ammonium  (magnesia  alone  cannot 
be  separated  perfectly  from  antimonic  acid  by  this  method).  The 
alkaline  earthy  arseniates  are  the  most  troublesome ; the  baryta, 
strontia,  and  lime  salts  usually  require  to  be  subjected  5 times  to  the 
operation,  before  they  are  free  from  arsenic,  and  the  arseniate  of 
magnesia  it  is  impossible  thoroughly  to  decompose  in  this  way  (H. 
BosEf). 

c.  Mercury  from  Gold  (Silver,  and  generally  from  the 
Non-volatile  Metals). 

Heat  the  weighed  alloy  in  a porcelain  crucible,  ignite  till  the  141 
weight  is  constant,  and  determine  the  mercury  from  the  loss.  If  it 
is  desired  to  estimate  it  directly,  the  apparatus,  fig.  50,  p.  222,  may 
be  used.  In  cases  where  the  separation  of  mercury  from  metals  that 
oxidize  on  ignition  in  the  air  is  to  be  effected  by  this  method,  the 
operation  must  be  conducted  in  an  atmosphere  of  hydrogen  (p.  181, 
fig.  47). 

9.  Volatility  of  Sulphide  of  Arsenic. 

Arsenic  Acid  from  the  Oxides  of  Manganese,  Iron,  Zinc, 
Lead,  Copper,  Nickel,  Cobalt  (not  of  Silver,  Aluminum,  or 
Magnesium). 

Mix  the  arsenic  acid  compound  (no  matter  whether  it  has  been  142 
air-dried  or  gently  ignited)  with  sulphur,  and  ignite  under  a good 
draught  in  an  atmosphere  of  hydrogen  (p.  181,  fig.  47 ; the  per- 
forated lid  must  in  this  case  be  of  porcelain).  The  whole  of  the 
arsenic  volatilizes,  the  sulphides  of  maganese,  iron,  zinc,  lead,  and 
copper  remain  behind ; they  may  be  weighed  directly.  After  weigh- 
ing, add  a fresh  quantity  of  sulphur  to  the  residue,  ignite  as  before, 


* Pogg.  Annal.  112,  169. 


f Ibid.  73,  582 ; 74,  578  ; 112,  173. 


§ 1«4.] 


OXIDES  OF  GROUP  VI. 


395 


and  weigh  again ; repeat  this  operation  until  the  weight  remains 
constant.  Usually,  if  the  compound  was  intimately  mixed  with 
the  sulphur,  the  conversion  of  the  arseniate  into  sulphide  is  com- 
plete after  the  first  ignition.  Results  very  good. 

In  separating  nickel  the  analyst  will  remember  that  the  residue 
cannot  be  weighed  directly,  since  it  does  not  possess  a constant  com- 
position ; hence  the  ignition  in  hydrogen  may  be  saved  ; arseniate 
of  nickel  loses  all  its  arsenic  on  being  simply  mixed  with  sulphur  and 
heated.  The  heat  should  be  moderate  and  continued,  till  no  more 
red  sulphide  of  arsenic  is  visible  on  the  inside  of  the  porcelain 
crucible.  It  is  advisable  to  repeat  the  operation.  The  separation  of 
arsenic  from  cobalt  cannot  be  completely  effected  in  this  manner  even 
by  repeated  treatment  with  sulphur,  but  it  can  be  effected  by  oxidiz- 
ing the  residue  with  nitric  acid,  evaporating  to  dryness,  mixing  with 
sulphur,  and  re-igniting.  Smaltine  and  cobaltine  must  be  treated  in 
the  same  manner  (H.  Rose*).  I should  not  forget  to  mention  that 
Ebelmen,!  a long  while  ago,  noticed  the  separation  of  arsenic  acid 
from  sesquioxide  of  iron  by  ignition  in  a stream  of  sulphuretted  hy- 
drogen. 

10.  Separation  of  Arsenic  as  Arseniate  of  Magnesia  and 
Ammonia. 

Arsenic  Acid  from  Oxide  of  Copper,  Oxide  of  Cadmium, 
Sesquioxide  of  Iron,  Protoxide  of  Manganese,  Protoxide  of 
Nickel,  Protoxide  of  Cobalt,  Alumina. 

Mix  the  hydrochloric  acid  solution,  which  must  contain  the  whole  143 
of  the  arsenic  in  the  form  of  arsenic  acid,  with  enough  tartaric  acid  to 
prevent  precipitation  by  ammonia,  precipitate  the  arsenic  acid  accord- 
ing to  § 127,  2,  as  arseniate  of  magnesia  and  ammonia,  allow  to  settle, 
filter,  wash  once  with  a mixture  of  3 parts  water  and  1 part  ammonia, 
redissolve  in  hydrochloric  acid,  add  a very  minute  quantity  of  tar- 
taric acid,  supersaturate  again  with  ammonia,  allow  to  deposit,  and 
determine  the  now  pure  precipitate  according  to  § 127,  2.  In  the 
filtrate  the  bases  of  Groups  I V . and  Y.  may  be  precipitated  by  sulphide 
of  ammonium ; if  alumina  is  present,  evaporate  the  solution  filtered 
from  the  sulphides  with  addition  of  carbonate  of  soda  and  a little 
nitre  to  dryness,  fuse,  and  estimate  the  alumina  in  the  residue.  The 
method  is  more  adapted  to  the  separation  of  rather  large  than  of  very 
small  quantities  of  arsenic  from  the  above  named  oxides,  since  in  the 
case  of  small  quantities  the  minute  portions  of  arseniate  of  magnesia 
and  ammonia  that  remain  in  solution  may  exercise  a considerable 
influence  on  the  accuracy  of  the  result.  [See  Editor’s  note  to 
§ 135  e,  a.] 

1 1 . Separation  of  Arsenic  as  Arseniomolybdate  of  Ammonia. 
Arsenic  Acid  from  all  Oxides  of  Groups  I. — V. 

Separate  the  arsenic  acid  as  directed  in  § 127,  2,  b ; long  continued  144 
heating  at  100°  is  indispensable.  The  determination  of  the  bases  is 
most  conveniently  effected  in  a special  portion  (comp.  § 135,  k.) 


* Zeitschrift  f.  anal.  Chem.  1,  413. 
f Anal,  de  Chim.  et  de  Phys.  (3)  xxv.  98. 


396 


SEPARATION. 


[§  164. 


12.  Insolubility  of  Arseniate  of  Sesquioxide  of  Iron. 

Arsenic  Acid  from  the  Bases  of  Groups  I.  and  II.,  and 

from  Oxide  of  Zinc,  and  the  Protoxides  of  Manganese,  Nickel, 
and  Cobalt. 

Precipitate  the  arsenic  acid,  according  to  circumstances,  as  di-  145 
rected  § 127,  3,  a or  b,  filter,  and  determine  the  bases  in  the  filtrate. 

13.  Methods  based  upon  the  Insolubility  of  some  Chlorides. 

a.  Silver  from  Gold. 

Treat  the  alloy  with  cold  dilute  nitrohydrochloric  acid,  dilute,  and  146 
filter  the  solution  of  the  terchloride  of  gold  from  the  undissolved 
chloride  of  silver.  This  method  is  applicable  only  if  the  alloy  con- 
tains less  than  15  per  cent,  of  silver ; for  if  it  contains  a larger 
proportion,  the  chloride  of  silver  which  forms  protects  the  unde- 
composed part  from  the  action  of  the  acid.  In  the  same  way  silver 
may  be  separated  also  from  platinum. 

b.  Oxide  of  Mercury  from  the  Oxygen  Compounds  of  Arsenic 
and  Antimony. 

Precipitate  the  mercury  from  the  hydrochloric  solution  by  means  147 
of  phosphorous  acid  as  subchloride  (§  118,  2,  a).  The  tartaric  acid, 
which  in  the  presence  of  antimony  must  be  added,  does  not  inter- 
fere with  the  reaction  (H.  Bose*). 

14.  Insolubility  of  certain  Sulphates  in  Water  or  Spirit  of 

Wine. 

a.  Arsenic  Acid  from  Baryta,  Strontia,  Lime,  and  Oxide  of 
Lead. 

Proceed  as  for  the  separation  of  phosphoric  acid  from  the  same  148 
oxides  (§  135,  b).  The  compounds  of  these  bases  with  arsenious 
acid  are  first  converted  into  arseniates,  before  the  sulphuric  acid  is 
added  ; this  conversion  is  effected  by  heating  the  hydrochloric  acid 
solution  with  chlorate  of  potassa. 

b.  Antimony  from  Lead. 

Treat  the  alloy  with  a mixture  of  nitric  and  tartaric  acids.  The  149 
solution  of  both  metals  takes  place  rapidly  and  with  ease.  Preci- 
pitate the  greater  part  of  the  lead  as  sulphate  (§  116,  3),  filter,  pre- 
cipitate with  sulphuretted  hydrogen,  and  treat  the  sulphides  ac- 
cording to  128  with  sulphide  of  ammonium,  in  order  to  separate 
the  antimony  from  the  lead  left  unprecipitated  by  the  sulphuric  acid 
(A.  Streng|). 

15.  Different  deportment  with  Cyanide  of  Potassium. 

Gold  from  Lead  and  Bismuth. 

These  metals  may  be  separated  in  solution  by  cyanide  of  potassium  150 
in  the  same  way  in  which  the  separation  of  mercury  from  lead  and 
bismuth  is  effected  (see  109).  The  solution  of  the  double  cyanide 
of  gold  and  potassium  is  decomposed  by  boiling  with  aqua  regia, 
and,  after  expulsion  of  the  hydrocyanic  acid,  the  gold  determined 
by  one  of  the  methods  given  in  § 123. 


Pogg.  Annal.  110,  536. 


f Ding,  polyt.  Journ.  151,  389. 


397 


§ 165.] 


OXIDES  OF  GROUP  VI. 


II.  Separation  of  the  Oxides  of  the  Sixth  Group  from  each 

other. 

§ 165. 

Index : — The  Nos.  refer  to  those  in  the  margin. 

Platinum  from  gold,  151,  162. 

“ tin,  antimony,  and  arsenic,  152. 

Gold  from  platinum,  151, 102. 

“ tin,  152,  161. 

“ antimony  and  arsenic,  152. 

Tin  from  platinum,  152. 

“ gold,  134,  152,  161, 

“ arsenic,  153,  157,  158,  160,  163. 

“ antimony,  154,  159,  160. 

Protoxide  of  tin  from  the  binoxide,  166. 

Antimony  from  platinum  and  gold,  152. 

“ arsenic,  154,  155,  158. 

“ tin,  154,  159,  160. 

Teroxide  of  antimony  from  antimonic  acid,  165. 

Arsenic  from  platinum  and  gold,  152. 

“ tin,  153,  157,  158,  160,  163. 

“ antimony,  154,  155,  158. 

Arsenious  acid  from  arsenic  acid,  156,  164. 

1.  Precipitation  of  Platinum  as  Potassiobichloride  of  Plat- 

inum. 

Platinum  from  Gold. 

Precipitate  from  the  solution  of  the  chlorides  the  platinum  as  di- 151 
rected  § 124,  b , and  determine  the  gold  in  the  filtrate  as  directed 
1 123,  b. 

2.  Volatility  of  the  Chlorides  of  the  inferior  Metals. 

Platinum  and  Gold  from  Tin,  Antimony,  and  Arsenic. 

Heat  the  finely  divided  alloy  or  the  sulphides  in  a stream  of  chlo-152 
rine  gas.  Gold  and  platinum  are  left,  the  chlorides  of  the  other 
metals  volatilize  (compare  50)* 

3.  Volatility  of  Arsenic  and  Persulphide  of  Arsenic. 


a. 


Arsenic  from  Tin  (H.  Pose). 


Convert  into  sulphides  or  into  oxides,  dry  at  100°,  and  heat  a 153 
weighed  portion  with  addition  of  a little  sulphur  in  a bulb-tube  or 
tray,  gently  at  first,  but  gradually  more  strongly,  conducting  a 
stream  of  dry  sulphuretted  hydrogen  gas  through  the  tube  during 
the  operation.  Sulphur  and  tersulphide  of  arsenic  volatilize,  sul- 
phide of  tin  is  left.  The  tersulphide  of  arsenic  is  received  in  U- 
tubes  containing  dilute  ammonia,  which  are  connected  with  the 
bulb-tube,  in  the  manner  described  in  119.  When  upon  continued 
application  of  heat  no  sign  of  further  sublimation  is  observed  in  the 
colder  part  of  the  bulb-tube,  drive  off  the  sublimate  which  has  col- 
lected in  the  bulb,  allow  the  tube  to  cool,  and  then  cut  it  off  above 
the  coating.  Divide  the  separated  portion  of  the  tube  into  pieces, 
and  heat  these  with  a little  solution  of  soda  until  the  sublimate  is 
dissolved  ; unite  the  solution  with  the  ammoniacal  fluid  in  the  re- 
ceiver, add  hydrochloric  acid,  then,  without  filtering,  chlorate  of 


398 


SEPARATION. 


[§  165. 


potassa,  and  heat  gently  until  the  tersulphide  of  arsenic  is  complete- 
ly dissolved.  Filter  from  the  sulphur,  and  determine  the  arsenic 
as  directed  § 127,  2.  The  quantity  of  tin  cannot  be  calculated  at 
once  from  the  blackish-brown  sulphide  of  tin  in  the  bulb,  since  this 
contains  more  sulphur  than  corresponds  to  the  formula  Sn  S.  It  is 
therefore  weighed,  and  the  tin  determined  in  a weighed  portion  of 
it,  by  converting  it  into  binoxide,  which  is  effected  by  moistening 
with  nitric  acid,  and  roasting  (§  126,  1,  c). 

Tin  and  arsenic  in  alloys  are  more  conveniently  converted  into 
oxides  by  cautious  treatment  with  nitric  acid.  If,  however,  it  is 
wished  to  convert  them  into  sulphides,  this  may  readily  be  effected 
by  heating  1 part  of  the  finely  divided  alloy  with  5 parts  of  car- 
bonate of  soda,  and  5 parts  of  sulphur,  in  a covered  porcelain  cru- 
cible, until  the  mass  is  in  a state  of  calm  fusion.  It  is  then  dis- 
solved in  water,  the  solution  filtered  from'  the  sulphide  of  iron,  &c., 
which  may  possibly  have  formed,  and  the  filtrate  precipitated  with 
hydrochloric  acid. 

If  the  tin  only  in  the  alloy  is  to  be  estimated  directly,  while  the 
arsenic  is  to  be  found  from  the  difference,  convert  as  above  directed 
into  sulphides  or  oxides,  mix  with  sulphur  and  ignite  in  a porcelain 
crucible  with  perforated  cover  in  a stream  of  sulphuretted  hydro- 
gen. The  residual  arsenic-free  protosulphide  of  tin  is  to  be  con- 
verted into  binoxide  and  weighed  as  such. 

4.  Methods  based  upon  the  insolubility  of  Antimoniate  of  Soda, 
a.  Antimony  from  Tin  and  Arsenic  (H.  Rose). 

If  the  substance  is  metallic,  oxidize  the  finely  divided  weighed  154 
sample,  in  a porcelain  crucible,  with  nitric  acid  of  1*4  sp.  gr.,  adding 
the  acid  gradually.  Dry  the  mass  on  the  water-bath,  transfer  to  a 
silver  crucible,  rinsing  the  last  particles  adhering  to  the  porcelain 
into  the  silver  crucible  with  solution  of  soda,  dry  again,  add  eight 
times  the  bulk  of  the  mass  of  solid  hydrate  of  soda,  and  fuse  for 
some  time.  Allow  the  mass  to  cool,  and  then  treat  with  hot  water 
until  the  undissolved  residue  presents  the  appearance  of  a fine 
powder ; dilute  with  some  water,  and  add  one  third  the  volume  of 
alcohol  of  0*83  sp.  gr.  Allow  the  mixture  to  stand  for  24  hours, 
with  frequent  stirring ; then  filter,  transfer  the  last  adhering  parti- 
cles from  the  crucible  to  the  filter  by  rinsing  with  dilute  spirit  of 
wine  (1  vol.  alcohol  to  3 vol.  water),  and  wash  the  undissolved 
residue  on  the  filter,  first  with  spirit  of  wine  containing  1 vol.  alco- 
hol to  2 vol.  water,  then  with  a mixture  of  equal  volumes  of  alcohol 
and  water,  and  finally  with  a mixture  of  3 vol.  alcohol  and  1 vol. 
water.  Add  to  each  of  the  alcoholic  fluids  used  for  washing  a few 
drops  of  solution  of  carbonate  of  soda.  Continue  the  washing 
until  the  color  of  a portion  of  the  fluid  running  off  remains  unal- 
tered upon  being  acidified  with  hydrochloric  acid  and  mixed  with 
sulphuretted  hydrogen  water. 

Rinse  the  antimoniate  of  soda  from  the  filter,  wash  the  latter 
with  a mixture  of  hydrochloric  and  tartaric  acids,  dissolve  the  an- 
timoniate in  this  mixture,  precipitate  with  sulphuretted  hydrogen, 
and  determine  the  antimony  as  directed  § 125,  1. 

To  the  filtrate,  which  contains  the  tin  and  arsenic,  add  hydro- 


OXIDES  OF  GROUP  VI. 


39? 


§ 165.] 


chloric  acid,  which  produces  a precipitate  of  arseniate  of  binoxide 
of  tin  ; conduct  now  into  the  unfiltered  fluid  sulphuretted  hydrogen 
for  some  time,  allow  the  mixture  to  stand  at  rest  until  the  odor  of 
that  gas  has  almost  completely  gone  off,  and  separate  the  weighed 
sulphides  of  the  metals  which  contain  free  sulphur,  as  in  153. 

If  the  substance  contains  only  antimony  and  arsenic , the  alco- 
holic filtrate  is  heated,  with  repeated  addition  of  water,  until  it 
scarcely  retains  the  odor  of  alcohol ; hydrochloric  acid  is  then 
added,  and  the  arsenic  acid  determined  as  arseniate  of  magnesia 
and  ammonia  (§  127,  2). 

b.  Small  quantities  of  the  sulphides  of  arsenic  and  antimony 
mixed  with  sulphur  are  often  obtained  in  mineral  analysis.  The 
two  metals  may  in  this  case  be  conveniently  separated  as  follows : 
Oxidize  the  precipitate  with  chlorine-free  red  fuming  nitric  acid, 
evaporate  the  solution  nearly  to  dryness ; mix  the  residue  with  a 
copious  excess  of  carbonate  of  soda,  add  some  nitrate  of  soda,  and 
treat  the  fused  mass  as  given  in  a.  If,  on  the  other  hand,  you  have 
a mixture  of  sulphides  of  tin  and  antimony  to  analyze,  oxidize  it 
with  nitric  acid  of  T5  sp.  gr.,  and  treat  the  residue  obtained  on 
evaporation  as  given  in  a. 

5.  Precipitation  of  Arsenic  as  Arseniate  of  Ammonia- 
Magnesia. 

a.  Arsenic  from  Antimony. 

Oxidize  the  metals  or  sulphides  with  nitrohydrochloric  acid  or  155 
hydrochloric  acid  and  chlorate  of  potassa,  or  with  chlorine  in  alka- 
line solution  (p.  327,  d.)  &)  ; add  tartaric  acid,  a large  quantity  of 
chloride  of  ammonium,  and  then  ammonia  in  excess.  (Should  the 
addition  of  the  latter  reagent  produce  a precipitate,  this  is  a proof 
that  an  insufficient  quantity  of  chloride  of  ammonium  or  of  tartaric 
acid  has  been  used,  which  error  must  be  corrected  before  proceeding 
with  the  analysis.)  Then  precipitate  the  arsenic  acid  as  directed 
§ 127,  2,  and  determine  the  antimony  in  the  filtrate  as  directed 
in  § 125,  1.  As  basic  tartrate  of  magnesia  might  precipitate  with 
the  arseniate  of  magnesia  and  ammonia,  the  precipitate  should 
always,  after  slight  washing,  be  redissolved  in  hydrochloric  acid, 
and  the  solution  reprecipitated  with  ammonia. — An  excellent 
method. 

b.  Arsenious  Acid  from  Arsenic  Acid. 

Mix  the  sufficiently  dilute  solution  with  a large  quantity  of  chlo- 156 
ride  of  ammonium,  precipitate  the  arsenic  acid  as  directed  § 127,  2, 
and  determine  the  arsenious  acid  in  the  filtrate  by  precipitation 
with  sulphuretted  hydrogen  (§  127,4).  Ludwig*  has  observed  that 
if  the  solution  is  too  concentrated,  arsenite  of  magnesia  falls  down 
with  the  arseniate  of  magnesia  and  ammonia,  hence  it  is  necessary 
to  dissolve  the  weighed  magnesia  precipitate  in  hydrochloric  acid 
and  test  the  solution  with  sulphuretted  hydrogen.  The  presence  of 
arsenious  acid  will  be  betrayed  by  the  immediate  formation  of  a 
precipitate. 


* Archiv  fur  Pharm.  97,  24. 


400 


SEPARATION. 


c.  Binoxide  of  Tin  from  Arsenic  Acid  (Lenssen*). 

The  oxides  obtained  by  oxidation  with  nitric  acid  are  digested  157 
with  ammonia  and  yellow  sulphide  of  ammonium,  and  the  arsenic 
precipitated  from  the  clear  solution  according  to  § 127,  2,  as  arseni- 
ate  of  magnesia  and  ammonia.  On  acidifying  the  filtrate  the  tin 
separates  as  bisulphide. 

6.  Behavior  of  the  Sulphides  towards  Bisulphite  of  Potassa. 

Arsenic  from  Antimony  and  Tin  (Bunsen!). 

If  freshly  precipitated  sulphide  of  arsenic  is  digested  with  sul- 158 
phurous  acid  and  sulphite  of  potassa,  the  precipitate  is  dissolved  ; 
on  boiling,  the  fluid  becomes  turbid  from  separated  sulphur,  which 
turbidity  for  the  most  part  disappears  again  on  long  boiling*  The 
fluid  contains,  after  expulsion  of  the  sulphurous  acid,  arsenite  and 
hyposulphite  of  potassa. 

[2  As  S3+8  (K  O,  2 S 02)=2  (KO,  As  03)  + 6(K  O,  S202)  + S3+7  S OJ 

The  sulphides  of  antimony  and  tin  do  not  exhibit  this  reaction. 

Both  therefore  may  be  separated  from  sulphide  of  arsenic  by  pre- 
cipitating the  solution  of  the  three  sulphides  in  sulphide  of  potas- 
sium with  a large  excess  of  aqueous  sulphurous  acid,  digesting  the 
whole  for  some  time  in  a water-bath,  and  then  boiling  till  two- 
thirds  of  the  water  and  the  whole  of  the  sulphurous  acid  are  ex- 
pelled. The  residuary  sulphide  of  antimony  or  tin  is  arsenic-free, 
the  filtrate  contains  the  whole  of  the  arsenic  and  may  be  immedi- 
ately precipitated  with  sulphuretted  hydrogen.  Bunsen  determines 
the  arsenic  by  oxidizing  the  dried  sulphide  together  with  the  filter 
with  fuming  nitric  acid,  diluting  the  solution  a little,  warming  gen- 
tly with  a little  chlorate  of  potassa  (in  order  to  oxidize  more  fully 
the  substances  formed  from  the  paper),  and  finally  precipitating  as 
arseniate  of  magnesia  and  ammonia. 

With  regard  to  the  separation  of  sulphide  of  tin  from  the  solu- 
tion of  arsenite  of  potassa  it  is  to  be  observed,  that  the  sulphide 
of  tin  must  be  washed  with  concentrated  solution  of  chloride  of 
sodium,  as,  if  water  were  used,  the  fluid  would  run  through  tur- 
bid. As  soon  as  the  precipitate  is  thoroughly  washed  with  the  chlo- 
ride of  sodium  solution,  the  latter  is  displaced  by  solution  of  ace- 
tate of  ammonia,  containing  a slight  excess  of  acetic  acid.  These 
last  washings  must  not  be  added  to  the  first,  as  the  acetate  of  am- 
monia hinders  the  complete  precipitation  of  the  arsenious  acid  by 
sulphuretted  hydrogen. 

The  test-analyses  adduced  by  Bunsen  show  very  satisfactory 
results. 

7.  Methods  based  upon  the  Separation  of  the  Metals  themselves , 
or  on  the  different  Deportment  of  the  same  with  Acids. 

a.  Tin  from  Antimony  [Tookey,|  Classen  ||]. 

[The  alloy  or  mixture  must  contain  8 — 10  times  as  much  tin  as  159 
antimony.  If  need  be,  add  a weighed  amount  of  pure  tin,  to  estab- 
lish this  proportion. 

* Annal.  d.  Chem.  u.  Pharm.  114,  116.  \ Ibid.  106,  3. 

X Joum.  Chem.  Soc.  xv.  462.  [|  Joum.  f.  prakt.  Chem.  xcii.  477. 


OXIDES  OF  GROUP  VI. 


401 


§ 165.] 

The  metals  are  dissolved  in  hydrochloric  acid  and  a little  nitric  acid, 
the  solution  is  heated  nearly  to  boiling,  and  then  piano  wire  (solu- 
ble without  residue  in  acids)  added  little  by  little  as  long  as  any  iron 
dissolves.  It  is  necessary  that  no  excess  of  metallic  iron  remain. 
Therefore,  when  all  the  antimony  appears  to  be  thrown  down  and 
all  the  iron  dissolved,  add  a little  hydrochloric  acid,  and  after  the 
precipitate  has  settled,  pour  off  the  clear  liquid  and  observe  whether 
iron  will  produce  any  further  precipitation.  It  is  thus  easy  to  be 
certain  that  all  the  antimony  is  separated,  and  that  it  is  unmixed 
with  metallic  iron.  Wash  the  antimony  with  hot  water  to  which 
at  first  a few  drops  of  hydrochloric  acid  are  added.  Finally,  dis- 
place the  water  that  adheres  to  the  precipitate  by  means  of  absolute 
alcohol,  and  the  latter  by  a few  drops  of  ether,  and  dry  at  100°. 

The  tin  is  separated  from  the  filtrate  by  sulphuretted  hydrogen.] 

b.  Much  Tin  from  little  Antimony  and  Arsenic. 

If  an  alloy  of  the  three  metals  is  treated  in  a very  finely  divided  160 
condition  in  a stream  of  carbonic  acid  with  strong  hydrochloric 
acid,  the  whole  of  the  tin  dissolves  to  protochloride.  A part  of 
the  arsenic  and  antimony  escapes  as  arsenetted  and  antimonetted 
hydrogen,  whilst  the  rest  remains  behind  in  the  state  of  metal,  or,  as 
the  case  may  be,  of  a solid  combination  with  hydrogen.  Conduct 
the  gas  through  several  U-tubes,  containing  a little  chlorine-free 
red  fuming  nitric  acid,  whereby  the  arsenic  and  antimony  will  be 
oxidized.  When  the  solution  is  effected,  dilute  the  contents  of  the 
flask  with  air-free  water  to  a certain  volume,  mix,  allow  to  settle 
and  determine  the  tin  in  an  aliquot  part,  either  gravimetrically 
or  volumetrically.  Filter  the  rest  of  the  fluid,  wash  the  precipitate 
thoroughly,  dry  the  filter  with  its  contents  in  a porcelain  crucible, 
add  the  contents  of  the  U-tubes,  evaporate  to  dryness,  and  in  the 
residue  separate  the  antimony  and  arsenic  as  directed  154- 

c.  Tin  from  Gold. 

Gold  may  be  separated  from  excess  of  tin  by  boiling  the  finely  161 
divided  alloy  with  only  slightly  diluted  sulphuric  acid,  to  which 
hydrochloric  acid  has  been  cautiously  added.  The  tin  dissolves  as 
protochloride.  Heat  is  applied  till  the  sulphuric  acid  begins  to 
volatilize  copiously.  Binoxide  of  tin  is  formed  which  dissolves  in 
the  concentrated  sulphuric  acid,  while  the  gold  remains  behind.  On 
addition  of  much  water,  the  binoxide  of  tin  falls,  mixed  with  finely 
divided  gold,  in  the  form  of  a purple-red  precipitate.  On  warming 
with  concentrated  sulphuric  acid  the  binoxide  of  tin  finally  redis- 
solves while  the  gold  is  left  pure  (H.  Bose*). 

d.  Platinum  from  Gold. 

The  aqua  regia  solution  is  freed  as  far  as  possible  from  nitric  acid  162 
by  evaporation  with  hydrochloric  acid,  and  treated  with  a solution 
of  protochloride  of  iron,  the  gold  being  determined  as  directed  § 

123,  b.  The  platinum  may  be  precipitated  from  the  filtrate  by  sul- 
phuretted hydrogen  according  to  § 124,  c. 

8.  Precipitation  of  Tin  as  Arseniate  of  the  P inoxide. 

Tin  from  Arsenic. 

E.  Haffely|  has  proposed  the  following  method  of  determin- 


Pogg.  Annal.  112,  172. 


26 


f Phil.  Mag.  x.  220. 


402 


SEPARATION. 


ing  both  the  tin  and  the  arsenic  in  commercial  stannate  of  soda,  163 
which  often  contains  a large  admixture  of  arseniate  of  soda.  Mix  a 
weighed  sample  with  a known  quantity  of  arseniate  of  soda  in  excess, 
add  nitric  acid  also  in  excess,  boil,  filter  off  the  precipitate,  which 
has  the  composition  2 Sn  02,  As  O5+10  aq.,  and  wash;  expel 
the  water  by  ignition,  and  weigh  the  residue,  which  consists  of  2 Sn 
02,  As  05.  In  the  filtrate  determine  the  excess  of  arsenic  acid  as 
directed  § 127,  2.  The  amount  of  the  binoxide  of  tin  is  found  from 
the  weight  of  the  precipitate,  that  of  the  arsenic  acid  is  obtained 
by  adding  the  quantity  in  the  precipitate  to  the  quantity  in  the  fil- 
trate, and  deducting  the  quantity  added. 

9.  Volumetric  Methods. 

a.  Arsenious  from  Arsenic  Acid. 

Convert  the  whole  of  the  arsenic  in  a portion  of  the  substance  164 
into  arsenic  acid  and  determine  the  total  amount  of  this  as  directed 
§ 127,  5,  b ; determine  in  another  portion  the  arsenious  acid  as  di- 
rected in  § 127,  5,  a,  and  calculate  the  arsenic  acid  from  th$  dif- 
ference. 

b.  Teroxide  of  Antimony  from  Antimonic  Acid. 

Determine  in  a sample  of  the  substance  the  total  amount  of  the  165 
antimony  as  directed  § 125,  1,  in  another  portion  that  of  the  terox- 
ide as  directed  § 125,  3,  and  calculate  the  antimonic  acid  from  the 
difference. 

c.  Protoxide  of  Tin  in  Presence  of  Binoxide. 

In  one  portion  of  the  substance  convert  the  whole  of  the  protox-166 
ide  into  binoxide  by  digestion  with  chlorine  water  or  some  other 
means,  and  determine  the  total  quantity  of  tin  as  directed  § 126, 

1,  6/  in  another  portion,  which,  if  necessary,  is  to  be  dissolved  in 
hydrochloric  acid  in  a stream  of  carbonic  acid,  determine  the  pro- 
toxide according  to  § 126,  2. 

II.  SEPARATION  OF  THE  ACIDS  FROM  EACH  OTHER. 

It  must  not  be  forgotten  that  the  following  methods  of  separation 
proceed  generally  upon  the  assumption  that  the  acids  exist  either 
in  the  free  state,  or  in  combination  with  alkaline  bases ; compare 
the  introductory  remarks,  p.  337*  Where  several  acids  are  to  be 
determined  in  one  and  the  same  substance,  we  very  often  use  a sep- 
arate portion  for  each.  The  methods  here  given  do  not  embrace 
every  imaginable  case,  but  only  the  most  important  cases,  and  those 
of  most  frequent  occurrence. 

first  group. 

ARSENIOUS  ACID — ARSENIC  ACID CHROMIC  ACID — SULPHURIC  ACID — 

PHOSPHORIC  ACID BORACIC  ACID OXALIC  ACID HYDROFLUORIC 

ACID SILICIC  ACID CARBONIC  ACID. 

§ 166. 

1.  Arsenious  Acid  and  Arsenic  Acid  from  all  other  Acids. 

Precipitate  the  arsenic  from  the  solution  by  means  of  sulphuretted  167 


ACIDS  OF  GROUP  I. 


403 


§ 166.] 


hydrogen  (§  127,  4,  a or  6),  filter,  and  determine  the  other  acids  in 
the  filtrate.  It  must  he  remembered,  that  the  tersulphide  of  arsenic 
will  be  obtained  mixed  with  sulphur  if  chromic  acid,  sesquioxide  of 
iron,  or  any  other  substances  which  decompose  sulphuretted  hydro- 
gen are  present. 

From  those  acids  which  form  soluble  salts  with  magnesia,  arsenic 
acid  may  be  separated  also  by  precipitation  as  arseniate  of  magnesia 
and  ammonia  as  directed  § 127,  2. 

2.  Sulphuric  Acid  from  all  the  other  Acids. 

a.  From  Arsenious , Arsenic , Phosphoric , Poracic , Hydrofluoric , 
Oxalic , Silicic , and  Carbonic  Acids  * 

Acidify  the  dilute  solution  strongly  with  hydrochloric  acid,  mix  168 
with  chloride  of  barium,  and  filter  the  sulphate  of  baryta  from  the 
solution,  which  contains  all  the  other  acids.  Determine  the  sulphate 
of  baryta  as  directed  § 132. 

If  acids  are  present  with  which  baryta  forms  salts  insoluble  in 
water  but  soluble  in  acids,  the  sulphate  of  baryta  is  apt  to  carry 
down  with  it  such  salts,  and  this  is  all  the  more  liable  to  happen, 
the  longer  the  precipitate  is  allowed  to  settle.  This  remark  applies 
especially  to  the  oxalate  and  tartrate  of  baryta  and  the  baryta  salts 
of  other  organic  acids  (H.  Rose).  In  such  cases  I would  recommend, 
after  washing,  to  stop  up  the  neck  of  the  funnel,  and  digest  the  pre- 
cipitate with  a solution  of  bicarbonate  of  soda,  then  to  wash  with 
water,  with  dilute  hydrochloric  acid,  and  again  with  water.  In 
every  case,  however,  the  purity  of  the  weighed  sulphate  of  baryta 
must  be  tested  as  directed  § 132,  1. 

b.  From  Hydrofluoric  Acid  in  Insoluble  Compounds . 

A mixture  of  sulphate  of  baryta  and  fluoride  of  calcium  cannot  189 
be  decomposed  by  simple  treatment  with  hydrochloric  acid  ; the  in- 
soluble residue  contains,  besides  sulphate  of  baryta,  sulphate  of  lime 
and  fluoride  of  barium.  The  object  in  view  may  be  attained,  how- 
ever, by  the  following  process  : — Fuse  the  substance  with  6 parts  of 
carbonate  of  soda  and  potassa,  and  2 parts  of  silicic  acid  ; allow  the 
mass  to  cool,  treat  with  water,  and  add  carbonate  of  ammonia  to  the 
solution  obtained ; filter,  wash  the  separated  silicic  acid  with  dilute 
solution  of  carbonate  of  ammonia,  supersaturate  the  filtrate  with  hy- 
drochloric acid,  and  precipitate  with  chloride  of  barium. 

If  you  wish  to  determine  the  fluoride  also,  acidify  with  nitric  acid, 
precipitate  with  nitrate  of  baryta,  then  saturate  with  carbonate  of 
soda,  and  precipitate  the  fluoride  of  barium  by  spirit  of  wine.  Wash  a 
long  time,  first  with  spirit  of  wine  of  50  per  cent.,  then  with  strong 
alcohol ; dry,  ignite,  and  weigh.  The  insoluble  residue  left  upon 
treating  with  water  contains  the  baryta  and  lime.  Dissolve  in  hydro- 
chloric acid,  separate  the  silicic  acid,  and  determine  the  bases  as 
directed  § 154  (JI.  Rose). 

c.  In  presence  of  a large  proportion  of  Chromic  Acid. 

Reduce  the  chromic  acid  by  boiling  the  dry  compound  with  con- 170 
centrated  hydrochloric  acid  (if  this  process  is  conducted  after  p.  258, 


* With  respect  to  the  separation  of  sulphuric  acid  from  selenic  acid,  comp. 
Wohlwill  (Anna!,  d.  Chem.  u.  Pharm.  114,  183). 


404 


SEPARATION. 


[§  166 


it  gives,  at  the  same  time,  the  quantity  of  the  chromic  acid)  ; dilute 
the  solution  largely,  and  precipitate,  first  the  sulphuric  acid  by  adding 
chloride  of  barium  in  slight  excess,  then  the  excess  of  baryta  by  sul- 
phuric acid,  and  lastly  the  sesquioxide  of  chromium  by  ammonia. 

d.  From  Hydrofluosilicic  Acid. 

Precipitate  the  hydrofluosilicic  acid  as  directed  § 133,  then  thesul- 171 
phuric  acid  in  the  filtrate  by  baryta. 

3.  Phosphoric  Acid  from  the  other  Acids. 

a.  From  the  acids  of  arsenic,  see  167  j from  sulphuric  acid,  see  172 

168. 

b.  From  Chromic  Acid. 

Precipitate  the  phosphoric  acid  as  phosphate  of  magnesia  and 
ammonia  (134,  b).  Determine  the  chromic  acid  in  the  filtrate  as 
directed  § 130,  a,  (5,  b,  c,  or  d. 

c.  From  Foracic  Acid. 

Precipitate  the  phosphoric  acid  with  a solution  of  chloride  of  mag- 173 
nesium  and  chloride  of  ammonium,  and  determine  it  as  pyrophos- 
phate of  magnesia  (§  134,  b).  Determine  the  boracic  acid  in  the 
filtrate  as  directed  § 136,  I.,  c. 

d.  From  Oxalic  Acid. 

a.  If  the  two  acids  are  to  be  determined  in  one  portion,  the  aqueous  174 
solution  is  mixed  with  sodio-terchloride  of  gold  in  excess, heat  applied, 
and  the  quantity  of  oxalic  acid  present  calculated  from  that  of  the 
reduced  gold  (§  137,  c,  a).  The  gold  added  in  excess  is  separated 
from  the  filtrate  by  means  of  sulphuretted  hydrogen,  and  the  phos- 
phoric acid  then  precipitated  by  sulphate  of  magnesia.  If  the  com- 
pound is  insoluble  in  water,  hydrochloric  acid  is  used  as  solvent,  and 
the  process  conducted  as  directed  § 137,  c,  /3. 

/3.  If  there  is  enough  of  the  substance,  the  oxalic  acid  is  deter-  175 
mined  in  one  portion  according  to  the  direction  of  § 137,  b or  d,  and 
the  phosphoric  acid  in  another  portion.  If  the  substance  is  soluble 
in  water,  and  the  quantity  of  oxalic  acid  inconsiderable,  the  phos- 
phoric acid  may  be  precipitated  at  once  with  sulphate  of  magnesia, 
chloride  of  ammonium,  and  ammonia  ; if  not,  the  substance  is  igni- 
ted with  carbonate  of  soda  and  potassa,  which  destroys  the  oxalic 
acid,  and  the  phosphoric  acid  is  determined  in  the  residue. 

e.  Phosphates  f rom  Fluorides. 

cl.  The  substance  is  soluble  in  water. 

aa.  If  the  substance  contains  a relatively  large  quantity  of  176 
fluorine,  which  will  permit  the  estimation  of  the  latter  from  the 
difference,  precipitate  the  solution  with  exclusion  of  air  by  chlo- 
ride of  calcium  with  addition  of  lime-water  to  alkaline  reaction, 
allow  to  deposit,  decant  through  a filter,  wash  the  precipitate, 
dry,  ignite,  and  weigh.  It  consists  of  phosphate  of  lime  and 
fluoride  of  calcium.  Heat  an  aliquot  part  in  a platinum  vessel, 
with  sulphuric  acid,  until  all  the  fluorine  has  escaped  as  hydro- 
fluoric acid,  taking  care  not  to  raise  the  heat  to  a degree  at 
which  sulphuric  acid  volatilizes  ; then  determine  the  lime  and 
the  phosphoric  acid  as  directed  § 135,  b.  By  deducting 
the  phosphoric  acid  and  lime  from  the  total  weight  of 


ACIDS  OF  GROUP  I. 


405 


§ 166.] 

the  precipitate,  the  fluorine  is  found  by  the  following  propor- 
tion : — 

The  eq.  of  fluorine  less  the  eq.  of  oxygen  : the  eq.  of  fluorine 

the  difference  found  : the  fluorine  sought. 

The  fluorine  may  be  determined  directly  in  another  aliquot 
part,  by  fusing  it  with  acid  pyrophosphate  of  soda,  and  calcula- 
ting the  fluorine  by  comparing  the  actual  loss  of  weight  with  that 
which  the  pyrophosphate  would  have  suffered  if  ignited  alone. 

2 (NaO,  HO,  P05)  + Ca  FI  = NaO,  P05  + NaO,  CaO,  P06 
-f  H FI  + HO. 

[bb.  If  the  substance  contains  a relatively  small  proportion  of  177 
fluorine,  this  should  be  determined  directly  by  Fresenius’  me- 
thod. (182.)  Phosphoric  acid  may  be  estimated  in  a portion  that 
has  been  evaporated  with  sulphuric  acid,  by  molybdic  solution 
(P.  271).] 

£.  The  substance  is  not  soluble  in  water , but  decomposable  by 
acids  {e.g.,  apatite,  bone-ash). 

Dissolve  in  hydrochloric  acid,  evaporate  with  sulphuric  acid,  as  in  178 
176,  until  the  fluorine  is  completely  expelled,  and  determine  in  the 
residue  the  phosphoric  acid  on  the  one  hand,  the  oxides  on  the  other 
hand.  Now,  if  you  know  the  proportion  between  the  phosphoric 
acid  and  the  bases  in  the  analyzed  compound,  you  may  readily  cal- 
culate the  expelled  fluorine  from  the  excess  of  the  bases,  the  oxygen 
of  the  latter  being  equivalent  to  the  fluorine.  Of  course,  it  is  taken 
for  granted  that  other  acids  are  absent,  or  are  determined  in  sepa- 
rate portions. 

y.  The  substance  is  insoluble  in  water  and  not  decomposable  by 
acids. 

Fuse  with  carbonate  of  soda  and  silicic  acid  as  in  169,  treat  the  179 
fused  mass  with  water,  and  the  solution  with  carbonate  of  ammonia. 

You  have  now  in  solution  the  whole  of  the  fluorine  and  phosphoric 
acid  in  combination  with  alkali  (H.  Rose),  and  may  accordingly 
proceed  as  in  176  or  177* 

4.  Fluorides  from  Borates. 

Mix  the  solution  containing  the  acids  in  combination  with  alkali  180 
with  some  carbonate  of  soda,  and  add  acetate  of  lime  in  excess.  A 
precipitate  is  formed,  which  contains  the  whole  of  the  fluorine  as 
fluoride  of  calcium,  and  besides  this,  carbonate  and  some  borate 
of  lime  ; the  greater  proportion  of  the  latter  having  been  redissolved 
by  the  excess  of  the  lime  salt  added.  Determine  the  fluoride  of  cal- 
cium in  the  precipitate  as  directed  in  § 138, 1.  The  small  quantity 
of  boracic  acid  in  the  precipitate  is,  in  this  process,  partly  volati- 
lized, partly  dissolved,  after  evaporating  the  mass  with  acetic  acid 
and  extracting  with  water.  It  is  therefore  necessary  to  determine 
the  boracic  acid  in  a separate  portion  of  the  substance  ; this  is 
effected  according  to  the  directions  of  § 136,  2 (A.  Stromeyer*). 

5.  Fluorides  from  Silicic  Acid  and  Silicates. 

A great  many  native  silicates  contain  fluorides  : care  must,  there- 
fore, always  be  taken,  in  the  analysis  of  minerals,  not  to  overlook 
the  latter. 


* Annal.  d.  Chem.  u.  Pharm.  100,  91. 


406 


SEPARATION, 


[§  166. 


If  the  silicates  containing  fluoride  are  decomposable  by  acids — 
(which  is  only  rarely  the  case) — and  the  silicic  acid  is  separated  in 
the  usual  way  by  evaporation,  the  whole  of  the  fluorine  may  vola- 
tilize. 

a.  Berzelius’s  method. 

Fuse  the  elutriated  substance  with  4 parts  of  carbonate  of  soda,  for  181 
some  time,  at  a strong  red  heat ; digest  the  mass  in  water,  boil, 
filter,  and  wash,  first  with  boiling  water,  then  with  solution  of  car- 
bonate of  ammonia.  The  filtrate  contains  all  the  fluorine  as  fluo- 
ride of  sodium,  and,  besides  this,  carbonate,  silicate,  and  aluminate 
of  soda.  Mix  the  filtrate  with  carbonate  of  ammonia,  and  heat 
the  mixture,  replacing  the  carbonate  of  ammonia  which  evapo- 
rates. Filter  off  the  precipitate  of  hydrate  of  silicic  acid  and 
hydrate  of  alumina,  and  wash  with  carbonate  of  ammonia.  Heat 
the  filtrate  until  the  carbonate  of  ammonia  is  completely  expelled, 
and  determine  the  fluorine  as  directed  § 138.  To  separate  the 
silicic  acid,  decompose  the  two  precipitates  with  hydrochloric  acid 
as  directed  § 140,  II.,  a.* 

b.  Wohler’s  method  modified  by  Fresenius.  (Suitable  for  the  182 
analysis  of  all  silicates  and  phosphates  which  are  readily  decomposed 

by  sulphuric  acid;  those  undecomposable  by  this  acid  must  be  fluxed.) 

[The  substance  must  be  reduced  to  an  impalpable  powder;  if  not  a 
silicate,  mixed  intimately  with  10  to  15  times  its  weight  of  finely  pul- 
verized quartz,  and  decomposed  in  a flask  with  pure  concentrated  sul- 
phuric acid  (sp.  gr.  1*848)  , at  a temperature  not  higher  than  160° 
nor  lower  than  150°  C.  The  fluorine  is  estimated  by  collecting  and 
weighing  the  fluoride  of  silicon  thus  evolved  (Fresenius),  or  by 
loss  (Wohler.)  The  former  is  the  only  accurate  method,  especially 
when  small  quantities  are  to  be  determined.  To  displace  fluoride 
of  silicon  completely  from  the  mixture  evolving  it,  long-continued 
aspiration  of  air  is  necessary.  The  apparatus  needful  consists  of 
a gasholder  of  20 — 30  litres  capacity,  which  should  be  filled  with  pure 
air  from  out-of-doors ; of  3 flasks  of  about  250  c.  c.  capacity  each ; and 
of  8 light  TJ-tubes,  whose  bore  is  12  mm.  and  whose  legs  are  10 — 12 
cm.  long.  Air  is  forced  from  the  gasholder, — firstly,  through  a 
flask  half  filled  with  strong  pure  sulphuric  acid,  then  through  a U- 
tube  containing  soda  lime,  and  again  through  a U-tube  filled  with 
glass  splinters  moistened  with  strong  sulphuric  acid.  The  air  thus 
freed  from  water  and  carbonic  acid  is  conducted  to  the  bottom  of  a 
second  flask,  containing  the  substance  under  examination  drenched 
with  a large  excess  of  sulphuric  acid.  This  flask  stands  over  a 
lamp  upon  a plate  of  cast-iron,  and  to  judge  of  the  temperature  of 
its  contents  another  flask  similarly  filled  with  sulphuric  acid,  in 
which  a thermometer  is  suspended  by  a loosely  fitting  cork,  is 
placed  upon  the  same  iron  plate,  the  lamp-flame  being  stationed  be- 
tween them  and  equidistant  from  both.  The  dry  air  streaming 
through  the  decomposing  flask,  heated  to  150° — 160°  carries  on  fluo- 
ride of  silicon  and  a little  vapor  of  sulphuric  acid,  firstly  into  an 


* The  whole  of  the  silicic  acid  may  be  removed  from  the  filtrate  by  the  treat- 
ment with  carbonate  of  ammonia : addition  of  carbonate  of  zinc  and  ammonia, 
as  recommended  by  Berzelius,  and  afterwards  by  Regnault,  appears  therefore 
superfluous  (H.  Rose). 


166.] 


ACIDS  OF  GROUP  I. 


407 


empty  U-tube,  and  then  into  another  containing,  in  the  first  half,  fused 
(anhydrous)  chloride  of  calcium,  and  in  the  second  half,  pumice,  im- 
pregnated with  anhydrous  sulphate  of  copper  (p.  289).  The  pure 
fluoride  of  silicon  is  finally  absorbed  in  the  three  remaining  U- 
tubes,  and  is  estimated  by  their  increase  of  weight.  Of  these  tubes, 
the  first  contains,  in  the  leg  next  the  decomposing  flask,  pumice 
moistened  with  water  between  two  cotton  plugs ; in  the  bend  and 
half  of  the  other  leg,  soda  lime  ; lastly,  fused  chloride  of  calcium  be- 
tween cotton  plugs.  The  weight  of  this  tube  should  be  40-50  grm. 

To  complete  the  absorption,  the  next  (seventh)  TJ-tube  is  filled  half 
with  fused  soda-lime  and  half  with  fused  chloride  of  calcium ; and 
the  last  (eighth)  contains  glass  splinters  wet  with  pure  and  strong 
sulphuric  acid,  to  completely  retain  traces  of  water,  which  would 
otherwise  be  carried  off  by  the  large  volume  of  heated  air. 

The  tubes  having  been  carefully  adjusted,  and  made  tight  by 
melting  sealing-wax  over  the  corks,  so  much  substance  is  placed  in 
the  decomposing  flask  as  to  yield,  if  possible,  0T  grm.  of  fluoride 
of  silicon.  If  a carbonate  be  present,  this  must  be  removed  by 
heating  the  weighed  substance  with  water  and  a slight  excess  of 
acetic  acid  (in  case  of  operating  with  a fluoride  soluble  in  water,  ace- 
tate of  lime  must  also  be  added).  After  the  carbonate  is  decom- 
posed, the  whole  is  evaporated  to  dryness  on  the  water-bath.  The 
residue  is  digested  and  washed  with  water,  dried,  separated  as  well 
as  possible  from  the  filter,  and  mixed  with  the  filter-ash.  The  sub- 
stance is  intimately  mixed,  if  needful,  with  ignited  quartz  powder 
transferred  to  the  decomposing  flask,  the  mortar  being  rinsed  with 
quartz-powder,  and  drenched  with  40 — 50  c.  c.  of  concentrated  sul- 
phuric acid.  The  flask  is  connected  with  the  tubes  on  either  side, 
and  with  frequent  shaking  is  gradually  brought  to  a temperature 
of  150° — 160°  C.  Incipient  decomposition  is  recognized  by  the  rise  of 
gas  bubbles  in  the  heated  liquid  (which  are  broken  by  agitation)  as 
well  as  by  deposition  of  silica  in  the  tube  containing  moist  pumice. 

As  soon  as  gas-bubbles  cease  to  appear,  which  commonly  happens  af- 
ter anhour,  when  small  quantities  (0T  grm.)  of  a fluorideare  employed, 
or  after  two  to  three  hours  when  larger  amounts  (1.0  grm.)  are  used, 
the  lamp  is  removed,  the  air  current  stopped,  and  the  three  weighed  ab- 
sorption tubes  are  weighed  again.  During  this  operation  the  break 
in  the  system  of  tubes  is  supplied  by  a straight  glass  tube.  After 
weighing,  the  three  tubes  are  replaced,  the  decomposing  flask  is 
heated  again  to  150°-160°  C„  the  air-current  is  re-established,  and 
the  experiment  continued  1-|-  hours.  If  the  tubes  suffer  no  fur- 
ther increase  of  weight,  the  operation  is  concluded ; otherwise  the 
heating,  &c.,  must  be  repeated  until  a constant  weight  is  obtained. 

F or  every  hour  during  which  the  air-current  has  been  passing  the 
apparatus,  deduct  0*001  grm.  from  the  total  increase  of  the  three 
absorption  tubes ; the  residue  is  fluoride  of  silicon.  This  multiplied 
by  J1^-— 1|—0-73077,  gives  the  fluorine.  Results  good.] 

6.  Fluorides,  Silicates,  and  Phosphates,  in  presence  of 

EACH  OTHER. 

Native  compounds  of  fluorides,  silicates,  and  phosphates  are  not  133 
uncommon.  They  are  decomposed  as  in  181.  Complete  decom- 
position of  the  phosphates  is  not  always  effected  in  this  process,  as 


408 


SEPARATION. 


[§  166. 


phosphate  of  lime,  for  instance,  is  only  partially  decomposed  by  fu« 
sion  with  carbonate  of  soda.  The  solution  remaining  after  the  re- 
moval of  the  silicic  acid  and  the  volatilization  of  the  carbonate  of 
ammonia,  contains — in  presence  of  phosphates — besides  fluoride  of 
sodium  and  carbonate  of  soda,  also  phosphate  of  soda. 

Neutralize  the  fluid  nearly  with  hydrochloric  acid,  precipitately 
with  chloride  of  calcium,  filter,  dry,  and  ignite  the  precipitate,  which 
consists  of  fluoride  of  calcium,  phosphate  of  lime,  and  carbonate  of 
lime ; treat  the  residue  with  acetic  acid  in  excess,  and  evaporate  on 
the  water-bath  to  dryness  and  complete  expulsion  of  the  acetic  acid  ; 
extract  the  acetate  of  lime,  into  which  the  carbonate  has  been  con- 
verted by  the  last  operation,  with  water ; weigh  the  residue,  which 
consists  of  phosphate  of  lime  and  fluoride  of  calcium ; and  treat  it 
further  as  directed  in  176.  In  the  original  residue  of  the  first 
operation  and  in  the  precipitate  thrown  down  by  carbonate  of  am- 
monia, determine  the  silicic  acid,  the  rest  of  the  phosphoric  acid, 
and  the  bases.  The  method  182  may  also  be  employed  for  estimat- 
ing fluorine. 

7.  Silicic  Acid  from  all  other  Acids. 

a.  In  Compounds  which  are  decomposed  by  Hydrochloric  Acid. 

Decompose  the  substance  by  more  or  less  protracted  digestion  185 

with  hydrochloric  acid  or  nitric  acid  evaporate  on  the  water-bath*  to 
dryness  (§  140,  II.,  a ),  and  treat  the  residue,  according  to  circum- 
stances, with  water,  hydrochloric  acid,  or  nitric  acid  ; filter  off  the 
residuary  silicic  acid,  and  determine  the  other  acids  in  the  filtrate. 

In  presence  of  boracic  acid  or  fluorine  this  method  is  inapplicable, 
and  the  process  described  in  b is  employed  instead.  If  carbonates 
are  present,  the  carbonic  acid  is  determined  in  a separate  portion  of 
the  substance. 

b.  In  Compounds  which  are  not  decomposed  by  Hydrochlorric 

Acid. 

Decompose  the  substance  by  fusion  with  carbonate  of  soda  andl86 
potassa  (§  140,  II.,  6,  a),  and  either  treat  the  residue  at  once  cau- 
tiously with  dilute  hydrochloric  or  nitric  acid,  and  the  solution  thus 
obtained  as  in  a ; or  boil  the  residue  with  water,  precipitate  the  dis- 
solved silicic  acid  from  the  solution  by  heating  with  bicarbonate  of 
ammonia,  filter,  and  in  the  mixed  residue  and  precipitate  determine 
the  silicic  acid  by  treating  with  hydrochloric  acid  and  proceeding 
as  directed  § 140,  II.,  a .,  in  the  filtrate,  determine  the  other  acids. 
Which  of  these  two  methods  may  be  preferable  in  particular  cases, 
depends  upon  the  nature  of  the  bases,  and  upon  the  proportion  which 
the  silicic  acid  bears  to  the  latter.  In  presence  of  boracic  acid  or 
fluorine,  the  latter  method  alone  is  applicable. 

8.  Carbonic  Acid  from  all  other  Acids. 

When  carbonates  are  heated  with  stronger  acids,  the  carbonicl87 
acid  is  expelled  ; the  presence  of  carbonates,  therefore,  does  not  in- 
terfere with  the  estimation  of  most  other  acids.  And  as,  on  the 
other  hand,  the  carbonic  acid  is  determined  by  the  loss  of  weight  or 
by  combination  of  the  expelled  gas,  the  presence  of  salts  of  non- 


* A higher  temperature  would  not  answer. 


ACIDS  OF  GROUP  II. 


409 


§ 167.] 

volatile  acids  does  not  interfere  with  the  determination  of  the  car- 
bonic acid.  Accordingly,  with  compounds  containing  carbonates, 
sulphates,  phosphates,  &c.,  either  the  carbonic  acid  is  determined  in 
one  portion  and  the  other  acids  in  another,  or  both  estimations  are 
performed  on  one  portion.  In  the  latter  case  the  process  de- 
scribed p.  293,  e,  may  be  used  with  advantage,  the  other  acids  be- 
ing determined  in  the  solution  remaining  in  the  decomposing  flask. 

In  presence  of  fluorides,  one  of  the  weak  non-volatile  acids,  such  as 
tartaric  acid  or  citric  acid,  must  be  employed  to  expel  the  carbonic 
acid;  since,  were  sulphuric  acid  or  hydrochloric  acid  used  for  the 
purpose,  part  of  the  liberated  hydrofluoric  acid  would  escape  with 
the  carbonic  acid.  If,  as  will  occasionally  happen  in  an  analysis, 
a mixed  precipitate  of  fluoride  of  calcium  and  carbonate  of  lime  is 
thrown  down  from  a solution,  the  two  salts  may  be  separated  by 
evaporating  with  acetic  acid  to  dryness,  and  extracting  the  residue 
with  water  ; the  acetate  of  lime  formed  from  the  carbonate  is  dis- 
solved, the  fluoride  of  calcium  is  left  behind. 

SECOND  GROUP. 

HYDROCHLORIC  ACID HYDROBROMIC  ACID HYDRIODIC  ACID 

HYDROCYANIC  ACID HYDROSULPHURIC  ACID. 

I.  Separation  of  the  Acids  of  the  Second  Group  from 

THOSE  OF  THE  FlRST. 

§ 167. 

a.  All  the  Acids  of  the  Second  Group  from  those  of  the  First. 

Mix  the  dilute  solution  with  nitric  acid,  add  nitrate  of  silver  in  188 
excess,  and  filter  off  the  insoluble  chloride,  bromide,  iodide,  &c.,  of 
silver.  The  filtrate  contains  the  whole  of  the  acids  of  the  first 
group,  the  silver  salts  of  these  acids  being  soluble  in  water  or  in 
nitric  acid.  Carbonic  acid  must,  under  all  circumstances,  be  deter- 
mined in  a separate  portion.  The  estimation  may  be  effected  after 
§ 139,  d,  or  e.  In  the  first  case  the  remarks  on  p.  289  must  be 
borne  in  mind. 

b.  Some  of  the  Acids  of  the  Second  Group  from  Acids  of  the 
First  Group. 

As  it  is  often  inconvenient  for  the  further  separation  of  the  acids  189 
of  the  second  group  to  have  them  all  in  the  form  of  insoluble 
silver  compounds,  the  analysis  is  sometimes  effected  by  separating 
first  the  acid  of  the  first  group,  then  that  of  the  second.  If  the 
quantity  of  disposable  substance  is  large  enough,  the  most  con- 
venient way  generally  is  to  determine  the  several  acids — e.g .,  sul- 
phuric acid,  phosphoric  acid,  chlorine,  sulphuretted  hydrogen,  &c. — 
in  separate  portions. 

Of  the  infinite  number  of  combinations  that  may  present  them- 
selves we  will  here  consider  only  the  most  important. 

1.  Sulphuric  Acid  may  be  readily  separated  from  chlorine,  bro-190 
mine,  iodine,  and  cyanogen,  by  precipitation  with  a salt  of  baryta. 

If  the  acids  of  the  second  group  are  to  be  determined  in  the  same 


410 


SEPARATION. 


[§  167. 

portion,  nitrate  of  baryta  or  acetate  of  baryta  is  used  instead  of  chlo- 
ride of  barium.  In  presence  of  sulphuretted  hydrogen,  sulphuric 
acid  cannot  be  determined  in  this  way,  as  part  of  the  sulphuretted 
hydrogen  would  be  converted  into  sulphuric  acid  by  the  oxygen  of 
the  air.  The  error  thus  introduced  into  the  process  may  be  very 
considerable  (Fresenius*).  The  sulphuretted  hydrogen  must,  there- 
fore, first  be  removed  by  addition  of  chloride  of  copper,  and  the  sul- 
phuric acid  determined  in  the  filtrate  ; or,  the  sulphuretted  hydro- 
gen must  be  completely  oxidized  into  sulphuric  acid  by  chlorine,  and 
a corresponding  deduction  afterwards  made  in  calculating  the  quan- 
tity of  the  sulphuric  acid. 

2.  Phosphoric  Acid  may  be  precipitated  by  means  of  nitrate  of  191 
magnesia  and  ammonia,  after  addition  of  nitrate  of  ammonia ; oxalic 
acid  by  nitrate  of  lime ; chlorine,  bromine,  iodine,  &c.,  are  deter- 
mined in  the  filtrate. 

3.  Chlorine  in  Silicates. 

a.  If  the  silicates  dissolve  in  dilute  nitric  acid,  precipitate  the  192 
highly  dilute  solution  with  nitrate  of  silver,  without  applying  heat ; 
remove  the  excess  of  silver  from  the  filtrate  by  dilute  hydrochloric 
acid,  still  without  applying  heat ; and  then  separate  the  silicic  acid  in 

the  usual  way. 

b.  If  the  silicate  becomes  gelatinous  upon  its  decomposition  with 
nitric  acid,  dilute,  allow  to  deposit,  filter,  wash  the  separated,  silicic 
acid,  and  treat  the  filtrate  as  in  a. 

c.  If  nitric  acid  fails  to  decompose  the  silicates,  mix  the  substance 
with  carbonate  of  soda  and  potassa,  moisten  the  mass  with  water, 
dry  in  the  crucible,  fuse,  boil  with  water,  remove  the  dissolved  silicic 
acid  by  means  of  carbonate  of  ammonia  and  then  precipitate,  after 
addition  of  nitric  acid,  with  nitrate  of  silver  (H.  Pose). 

4.  Chlorides  in  presence  of  Fluorides. 

If  the  substance  is  soluble  in  water,  the  separation  maybe  effected  193 
as  directed  in  183;  but  it  is  more  convenient  to  precipitate  the 
fluorine  with  nitrate  of  lime,  and  the  chlorine  in  the  filtrate  with 
nitrate  of  silver.  Insoluble  compounds  are  fused  with  carbonate  of 
soda  and  silicic  acid. 

5.  Chlorine  in  presence  of  Fluorine  in  Silicates. 

Proceed  as  directed  18  . Saturate  the  alkaline  filtrate  nearly  19  4 
with  nitric  acid,  precipitate  with  nitrate  of  lime,  separate  the  fluoride 
of  calcium  and  the  carbonate  of  lime  as  directed  in  187,  and  precipi- 
tate the  chlorine  in  the  filtrate  by  nitrate  of  silver. 

6.  Sulphides  in  Silicates. 

If  the  substance  is  decomposable  by  acids,  reduce  it  to  the  veryl95 
finest  powder,  and  treat  with  fuming  nitric  acid  free  from  sulphuric 
acid  (§  148  II.,  2,  a , p.  326).  When  the  sulphur  is  completely  oxi- 
dized, dilute,  filter  off  the  silicic  acid,  add  carbonate  of  ammonia  to 
the  filtrate,  to  remove  the  portion  of  silicic  acid  which  may  possibly 
have  dissolved ; filter  again,  and  determine  in  the  filtrate  the  sulphu- 


Journ.  f.  prakt.  Chem.  70,  9. 


§ 168.] 


ACIDS  OF  GROUP  II. 


411 


ric  acid  formed.  If,  on  the  contrary,  the  substance  is  not  de- 
composable by  acids,  fuse  with  4 parts  of  carbonate  of  soda  and  1 
part  of  nitrate  of  potassa,  boil  the  fused  mass  with  water,  filter,  re- 
move the  dissolved  silicic  acid  from  the  filtrate  by  carbonate  of  am- 
monia ( 181),  filter  again,  and  determine  in  the  filtrate  the  sulphu- 
ric acid  produced  from  the  sulphur. 

Supplement. 

Analysis  of  Compounds,  containing  Sulphides  of  the  Alkali 

Metals,  and  Alkaline  Carbonates,  Sulphates,  and  Hypo- 
sulphites. 

1 168. 

The  following  method  was  first  employed  by  G.  Werther  * in  the  19 
examination  of  gunpowder  residues. 

- Put  the  substance  into  a flask,  add  water,  in  which  a sufficient 
quantity  of  carbonate  of  cadmium f is  suspended;  cork,  and  shake 
the  vessel  well.  The  sulphide  of  the  alkali  metal  decomposes  com- 
pletely with  the  carbonate  of  cadmium.  Filter  the  yellowish  precipi- 
tate off,  and  treat  it  with  dilute  acetic  acid  (not  with  hydrochloric) ; 
the  carbonate  of  cadmium  dissolves,  the  sulphide  of  cadmium  is  left 
undissolved.  Oxidize  the  latter  with  chlorate  of  potassa  and  nitric 
acid  (p.  327),  and  precipitate  with  chloride  of  barium  the  sulphu- 
ric acid  formed  from  the  sulphide. 

Heat  the  fluid  filtered  from  the  yellow  precipitate,  and  mix  with 
solution  of  neutral  nitrate  of  silver.  The  precipitate  thrown  down 
by  that  reagent  consists  of  carbonate  of  silver  and  sulphide  of  silver 
(K  O,  SA+Ag  O,  N 05=K  O,  S 03  + Ag  S-bN  05).  Remove 
the  former  salt  by  means  of  ammonia,  and  precipitate  the  silver  from 
the  ammoniacal  solution — after  acidifying  with  nitric  acid — by  means 
of  chloride  of  sodium.  Each  1 eq.  chloride  of  silver  so  obtained  cor- 
responds to  1 eq.  carbonate. J Dissolve  the  sulphide  of  silver  in 
dilute  boiling  nitric  acid,  determine  the  silver  in  the  solution  as 
chloride  of  silver,  and  calculate  from  the  result  the  quantity  of  the 
hyposulphite ; 1 eq.  Ag  Cl  corresponds  to  2 eq.  sulphur  in  hyposul- 
phurous  acid,  and  accordingly  to  1 eq.  hyposulphite  (K  O,  SA). 

From  the  fluid  filtered  from  the  sulphide  and  carbonate  of  silver 
remove  first  the  excess  of  silver  by  means  of  hydrochloric  acid,  and 
then  precipitate  the  sulphuric  acid  by  a salt  of  baryta.  From  the 
sulphuric  acid  found  you  have,  of  course,  to  deduct  the  quantity  of 
that  acid  resulting  from  the  decomposition  of  the  hyposulphurous 
acid,  and  accordingly  for  1 part  by  weight  of  chloride  of  silver 
formed  from  the  sulphide,  O' 28  parts  by  weight  of  sulphuric  acid. 

The  difference  gives  the  amount  of  sulphuric  acid  originally  present 
in  the  analyzed  compound.  By  way  of  control,  you  may  determine, 
in  the  fluid  filtered  from  the  sulphate  of  baryta,  the  alkali  as  sul- 
phate as  directed  in  § 97  or  § 98. 

* Journ.  f.  prakt.  Chem.  55,  22. 

f To  obtain  the  carbonate  of  cadmium  free  from  alkali,  carbonate  of  ammonia 
must  be  used  as  precipitant. 

X A quantity  equivalent  to  the  sulphide  found  has  to  be  deducted  from  this 
(K  S + Cd  0,  C 0,=Cd  S+KO,C  Oa). 


412 


SEPARATION. 


L§  169. 


II.  Separation  of  the  Acids  of  the  Second  Group 

FROM  EACH  OTHER. 

§ 169. 

1.  Chlorine  from  Bromine. 

All  the  methods  of  direct  analysis  hitherto  proposed  to  effect 
the  separation  of  chlorine  from  bromine  are  defective.  The  bro- 
mine is  therefore  usually  determined  indirectly. 

a.  Precipitate  with  nitrate  of  silver,  wash  the  precipitate,  dry,  197 
fuse,  and  weigh.  Transfer  an  aliquot  part  of  the  mixed  chloride 
and  bromide  of  silver  to  a light  weighed  bulb-tube,*  fuse  in  the 
bulb,  let  the  mass  cool,  and  weigh.  This  operation  gives  both  the 
total  weight  of  the  tube  with  its  contents,  and  the  weight  of  the 
portion  of  mixed  chloride  and  bromide  of  silver  in  the  bulb.  The 
greatest  accuracy  in  the  several  weighings  is  indispensable.  Now 
transmit  through  the  tube  a slow  stream  of  dry  pure  chlorine  gas, 
heat  the  contents  of  the  bulb  to  fusion,  and  shake  the  fused  mass 
occasionally  about  in  the  bulb.  After  the  lapse  of  about  20  min- 
utes, take  off  the  tube,  allow  it  to  cool,  hold  it  in  an  oblique  posi- 
tion, that  the  chlorine  gas  may  be  replaced  by  atmospheric  air,  and 
then  weigh.  Heat  once  more,  for  about  10  minutes,  in  a stream  of 
chlorine  gas,  and  weigh  again.  If  the  two  last  weighings  agree,  the  ex- 
periment is  terminated;  if  not,  the  operation  must  be  repeated  once 
more.  The  loss  of  weight  suffered,  multiplied  by  4*2203  gives  the 
quantity  of  the  bromide  of  silver  decomposed  by  the  chlorine.  For 
the  proof  of  this  rule  see  § 197. 

This  method  gives  very  accurate  results,  if  the  proportion  of  bro- 
mine present  is  not  too  small ; but  most  uncertain  results  in  cases 
where  mere  traces  of  bromine  have  to  be  determined  in  presence  of 
large  quantities  of  chlorides,  as  for  instance  in  salt-springs.  To 
render  the  method  available  in  such  cases,  the  great  point  is  to  pro- 
duce a silver  compound  containing  all  the  bromine,  and  only  a small 
part  of  the  chlorine.  This  end  may  be  attained  in  several  ways. 

In  these  processes  the  quantity  of  chlorine  is  found  by  completely 
precipitating  a separate  portion  with  silver  solution,  and  deducting 
the  bromide  of  silver  found  from  the  weight  of  the  precipitate. 

a.  Mix  the  solution  with  carbonate  of  soda  in  excess,  filter  if  ne- 
cessary, evaporate  nearly  to  dryness,  extract  the  residue  with  hot 
absolute  alcohol ; the  solution  contains  the  whole  of  the  alkaline 
metallic  bromide,  and  only  a small  portion  of  the  alkaline  metallic 
chloride ; add  a drop  of  soda  solution,  and  evaporate ; dissolve  the 
residue  in  water,  acidify  with  nitric  acid,  and  precipitate  with 
silver  solution. 

j3.  Fehling’s  method,  f 

Mix  the  solution  cold  with  a quantity  of  solution  of  nitrate  of  198 
silver  not  nearly  sufficient  to  effect  complete  precipitation,  shaking 
the  mixture  vigorously,  and  leave  the  precipitate  for  some  time  in 
the  fluid,  with  repeated  shaking.  If  the  amount  of  the  precipitate 

* The  best  way  of  effecting  the  removal  of  the  fused  mass  from  the  crucible 
is  to  fuse  again,  and  then  pour  out. 
f Joum.  f.  prakt.  Chem.  45,  269. 


§ 169.] 


ACIDS  OF  GROUP  II. 


413 


produced  corresponds  at  all  to  the  quantity  of  bromine  present,  the 
whole  of  the  latter  substance  is  obtained  in  the  precipitate. 

Fehling  gives  the  following  rule  : — 

If  the  fluid  contains  0T$  bromine,  use  \ or  $ the  quantity  of  so- 
lution of  nitrate  of  silver  that  would  be  required  to  effect  complete 
precipitation;  if  0*01$,  y1^;  if  0*002$,  if  0*001$, 

Wash  the  mixed  precipitate  of  chloride  and  bromide  of  silver 
thoroughly  ; dry,  ignite,  weigh,  and  treat  with  chlorine,  as  above. 

y.  Marchand*  has  slightly  modified  Fehling’s  method.  Hel99 
reduces  with  zinc  the  mixed  precipitate  of  chloride  and  bromide  of 
silver  obtained  by  Fehling’s  fractional  precipitation ; decomposes 
the  solution  of  chloride  and  bromide  of  zinc  with  carbonate  of 
soda;  evaporates  to  dryness,  and  extracts  the  residue  with  absolute 
alcohol,  which  dissolves  all  the  bromide  of  sodium  with  only  a little 
of  the  chloride  of  sodium ; he  then  evaporates  the  solution  to  dry- 
ness, takes  up  the  residue  with  water,  precipitates  again  with  solu- 
tion of  nitrate  of  silver,  and  subjects  a part  of  the  weighed  preci- 
pitate to  the  treatment  with  chlorine. 

8.  If  a fluid  containing  chlorides  in  presence  of  some  bromide,  is 
heated,  in  a distillation  flask,  with  hydrochloric  acid  and  binoxide 
of  manganese,  the  whole  of  the  bromine  passes  over  before  any  of 
the  chlorine.  Upon  this  circumstance,  Mohr  f bases  the  following 
method  for  effecting  the  concentration  of  bromine : — 

Distil  as  stated,  and  conduct  the  vapors,  through  a doubly  bent 
tube,  into  a wide  Woulf’s  bottle,  which  contains  some  strong  solu- 
tion of  ammonia.  Dense  fumes  form  in  the  bottle,  filling  it  gra- 
dually. Conduct  the  excess  of  vapors  from  the  first  into  a second 
bottle,  with  narrow  neck,  which  contains  ammoniated  water.  Both 
bottles  must  be  sufficiently  large  to  allow  no  vapors  to  escape. 
When  the  whole  of  the  bromine  is  evolved,  which  may  be  distinctly 
seen  by  the  color  of  the  space  above  the  liquid  in  the  distillation 
flask  and  tubes,  raise  the  cork  of  the  flask  to  prevent  the  receding 
of  bromide  of  ammonium  fumes.  Let  the  apparatus  cool,  and 
unite  the  contents  of  the  two  bottles ; the  fluid  contains  the  whole 
of  the  bromine,  with  a relatively  small  portion  of  the  chlorine. 

b.  Instead  of  treating  the  mixed  chloride  and  bromide  of  silver  290 
in  a current  of  chlorine  as  in  a,  it  may  also  be  reduced  to  metallic 
silver  in  a current  of  hydrogen.  After  accurately  determining  the 
weight  of  the  reduced  metal,  calculate  the  amount  of  chloride  of 
silver  equivalent  to  it ; subtract  from  this  the  weight  of  the  chloride 
and  bromide  of  silver  subjected  to  the  reducing  process,  and  we 
have  the  same  difference  as  served  in  a for  the  point  of  departure 

of  the  calculation  (Wackenroder).  It  will  be  seen  that  one  and 
the  same  portion  of  mixed  bromide  and  chloride  of  silver  may  be 
treated  first  as  directed  in  then,  by  way  of  control,  as  directed  in 
b.  The  difference  found  in  the  direct  way  in  the  first,  and  by  cal- 
culation in  the  second  experiment,  between  the  weight  of  the  mixed 
chloride  and  bromide  of  silver  and  the  amount  of  chloride  of  silver 
equivalent  to  it,  must  be  the  same. 

c.  Pisani  recommends  to  add  a known  quantity  of  solution  of201 
nitrate  of  silver  in  slight  excess,  filter,  and  determine  the  silver  in 


* Journ.  f.  prakt.  Chem.  47,  363. 


f Anna!,  d.  Chem.  u.  Pharm.  93,  80. 


414 


SEPARATION. 


L§  169. 


the  filtrate  by  iodide  of  starcb  (p.  215).  The  precipitate  is  weighed 
as  in  c.  This  method  precludes  the  partial  precipitation. 

d.  Determine  in  a portion  of  the  solution  the  chlorine-}- bromine  202 
(by  precipitating  with  solution  of  silver),  either  gravimetrically  or 
volumetrically ; in  another  portion  the  bromine,  either  by  the  colori- 
metric method  (§  143, 1.,  c),  or  by  the  volumetric  method  (§  143, 1., 
b).  Calculate  the  chlorine  from  the  difference.  The  method  is 
very  suitable  for  an  expeditious  analysis  of  mother-liquors. 

2.  Chlorine  from  Iodine. 

a.  Proceed  exactly  as  for  the  indirect  determination  of  bromine  203 
in  presenec  of  chlorine  (197)-  The  loss  of  weight  suffered  by  the 
silver  precipitate  in  the  fusion  in  chlorine  gas,  multiplied  by  2*567, 
gives  the  quantity  of  the  iodide  of  silver  decomposed  by  chlorine. 

The  methods  described  in  200  and  201,  may  also  be  employed. 

The  results  obtained  by  these  methods  in  the  case  of  chlorine  and 
iodine  are  still  more  accurate  than  in  the  case  of  chlorine  and 
bromine,  as  the  equivalents  of  iodine  and  chlorine  differ  far  more 
widely  than  those  of  chlorine  and  bromine. 

b.  Add  to  the  solution  \ c.  c.  of  standard  solution  of  iodide  of204 
starch  (p.  215),  then,  drop  by  drop,  with  stirring,  standard  solution 

of  silver  (p.  304),  until  the  iodide  of  starch  is  decolorized.  The 
amount  of  silver  solution  used  (after  deducting  the  small  quantity 
required  for  the  decolorization  of  the  \ c.  c.  of  iodide  of  starch 
solution  added,  and  which  must  be  separately  determined)  corre- 
sponds exactly  to  the  amount  of  iodine  in  the  analyzed  compound ; 
for  iodide  of  starch  is  decolorized  before  the  precipitation  of 
chlorine  begins.  To  determine  now  the  chlorine  also,  add  again 
solution  of  nitrate  of  silver  in  slight  excess,  filter,  and  determine 
the  excess  of  silver  in  the  filtrate  by  means  of  iodide  of  starch 
(p.  215).  Deduct  the  amount  of  solution  of  nitrate  of  silver  cor- 
responding to  the  ^ c.  c.  of  iodide  of  starch  solution  added,  and  to  „ 
the  iodine  present,  as  well  as  the  excess  of  silver  solution  from  the 
total  quantity  added,  and  calculate  the  chlorine  from  the  difference. 

This  method  is  expeditious ; the  results  are  accurate  (Pisani*). 
Compare  also  Expt.  No.  94. 

The  following  methods  are  especially  adapted  for  the  determina- 
tion of  small  quantities  of  iodide  in  the  presence  of  large  quanti- 
ties of  chloride  : — 

c.  Mix  the  solution  with  a few  drops  of  solution  of  hyponitric  205 
acid  in  sulphuric  acid,  or  with  red  fuming  nitric  acid,  add  4 to  5 
grm.  bisulphite  of  carbon,  shake  violently,  separate  the  violet-colored 
bisulphide  from  the  fluid  containing  the  chlorine  (and  bromine)  by 
cautious  decantation,  and  shake  the  decanted  fluid  with  fresh  bisul- 
phide. After  the  violet  bisulphide  has  been  washed  by  decantation, 

the  water  being  poured  off  through  a filter,  the  iodine  may  be  deter- 
mined as  follows  : The  solution  should  be  in  a stoppered  bottle, 
covered  with  a layer  of  water.  Add  a dilute  solution  of  hyposul- 
phite of  soda,  with  shaking,  finally  after  addition  of  every  two 
drops.  The  violet  coloration  gradually  disappears.  The  end-point 
is  easy  to  hit  with  perfect  certainty.  Now  determine  the  value  of 


* Compt.  rend.  44,  352 ; Joum.  f.  prakt.  Chem.  72,  266. 


8 169.1 

f -J 


ACIDS  OF  GROUP  II. 


415 


the  solution  of  hyposulphite,  by  shaking  a few  c.  c.  of  standard 
iodine  solution  with  bisulphide  of  carbon,  and  then  adding  hyposul- 
phite to  decoloration.  Results  good. 

d.  Precipitate  a portion  with  silver  solution  and  determine  the  206 
chlorine  -f-  iodine ; in  a second  portion  estimate  the  iodine  volu- 
metrically  (§  145,  I.,  c,  or  d ),  and  calculate  the  chlorine  from  the 
difference. 

e.  For  technical  purposes  the  following  method  is  also  suitable.  It  207 
was  recommended  by  Wallace  and  Lamont*  for  the  estimation  of 
iodine  in  kelp.  The  kelp-lie  is  nearly  neutralized  with  nitric  acid, 
evaporated  to  dryness,  and  the  residue  fused  in  a platinum  vessel 

to  oxidation  of  all  the  sulphides.  Treat  with  water,  filter,  add 
nitrate  of  silver  till  the  precipitate  appears  perfectly  white,  wash, 
digest  with  strong  ammonia,  and  weigh  the  residual  iodide  of  silver. 
Finally,  add  to  the  weight  of  the  latter  the  amount  which  passes 
into  solution  in  the  ammonia ; it  is  24V  a aqueous  ammonia 

(sp.  gr.  0’89)  used. 

3.  Chlorine,  Bromine,  and  Iodine  from  each  other. 

a.  Determine  in  a portion  of  the  compound  the  chlorine,  bro-  208 
mine  and  iodine,  jointly  by  precipitation  with  nitrate  of  silver. 
Determine  the  silver  in  the  weighed  precipitate  as  in  200.  Or 
add  a known  quantity  of  solution  of  nitrate  of  silver  in  slight  excess, 
filter,  and  determine  the  small  excess  of  silver  in  the  filtrate  by 
means  of  iodide  of  starch  (201). 

Determine  the  iodine  separately  by  Dupre’s  method  (see  below), 
calculate  the  quantity  of  iodide  of  silver  and  of  silver  corresponding 
to  the  amount  of  iodine  found,  deduct  the  calculated  amount  of  iodide 
of  silver  from  the  mixed  iodide,  chloride,  and  bromide  of  silver,  that 
of  the  silver  from  the  known  quantity  of  the  metal  contained  in  the 
mixed  compound  ; the  remainders  are  respectively  the  joint  amount 
of  chloride  and  bromide  of  silver,  and  the  quantity  of  the  metal  con- 
tained therein ; these  are  the  data  for  calculating  the  chlorine  and 
bromine  (200)* 

As  regards  the  estimation  of  iodine  in  presence  of  bromides,  A. 
and  F.  .Dupre  found  that  if  the  solution  of  an  iodide  contains  1 
part  of  bromide  of  potassium,  or  more,  in  1500  parts  of  water, 
protobromide  of  iodine  (I  Br)  is  formed  upon  addition  of  chlorine 
water ; if  the  solution  contains  less  than  1 part  of  bromide  of  potas- 
sium in  1500  parts  of  water,  higher  bromides  in  varying  propor- 
tions are  formed  in  addition  to  the  protobromide.  If  the  solution 
contains  only  1 part  of  bromide  of  potassium  to  13000  parts  of 
water,  pentabromide  of  iodine  alone  is  formed.  If  the  iodine  was 
dissolved  in  bisulphide  of  carbon,  the  conversion  into  I Br  is 
marked  simply  by  the  change  of  the  violet  color  of  the  fluid  to  yel- 
lowish brown  (zirconium  color),  whereas  the  formation  of  I Br5  is 
marked  by  the  change  of  violet  to  white. 

Upon  these  reactions  A.  and  F.  Dupre  have  based  the  following 
method  : — Test  the  fluid  first  by  adding  bisulphide  of  carbon,  and 
then,  gradually,  chlorine  water,  to  see  whether  the  color  will  change 
from  violet  to  white.  If  this  is  not  the  case,  dilute  to  the  required 


Chem.  Gaz.  1859,  137. 


416 


SEPARATION. 


degree,  and  to  make  quite  sure,  add  one-half  more  water ; then  pro- 
ceed as  directed  § 145,  I.,  c,  a or  /?.  A.  and  F.  Dupre  obtained 
most  satisfactory  results  by  this  process  ; the  method  is  particular- 
ly recommended  for  the  determination  of  small  quantities  of  iodine 
in  lies  which  contain  large  quantities  of  chlorides,  and  not  too 
small  quantities  of  bromides.  If  the  latter  are  too  small,  exact  re- 
sults cannot  be  obtained  by  the  indirect  method,  on  which  the  bro- 
mine estimation  is  based.  To  determine  bromine  directly,  we  may, 
after  adding  a sufficient  quantity  of  chlorine  water  to  destroy  the 
violet  color  of  the  bisulphide,  and  consequently  to  form  I Cl5,  or, 
as  the  case  may  be,  I Br5  (6  eq.  chlorine  = 1 eq.  iodine),  add  more 
chlorine  water  till  the  whole  of  the  bromine  is  converted  into  Br 
Cl.  2 eq.  of  this  second  quantity  of  chlorine  correspond  to  1 eq. 
bromine  (A.  Reimann).  The  details  will  be  found  § 143,  I.,  b. 

To  explain,  I will  suppose  the  case  in  which  5 eq.  K Br  and  1 eq. 

K I are  present.  K I -f  5 K Br  -f  6 Cl  = 6 K Cl  + I Br6  and  I 
Br5  + 10  Cl  = I Cl5  + 5 Br  Cl. 

b.  Proceed  generally  as  in  a , but  determine  the  iodine  by  Pisani’s  209 
method  (204).  This  method  also  gives  very  satisfactory  results, 
especially  in  the  presence  of  large  quantities  of  iodides.  Presence 
of  bromides  does  not  interfere  with  the  accuracy  of  the  estimation 
of  the  iodine  (Expt.  No.  95). 

4.  Analysis  of  Iodine  containing  Chlorine. 

a.  Dissolve  a weighed  quantity  of  the  dried  iodine  in  cold  sul-  210 
phurous  acid,  precipitate  with  solution  of  nitrate  of  silver,  digest 
the  precipitate  with  nitric  acid,  to  remove  the  sulphite  of  silver 
which  may  have  coprecipitated,  and  weigh.  The  calculation  of  the 
iodine  and  chlorine  is  made  by  the  following  equations,  in  which 
A represents  the  quantity  of  iodine  analyzed,  x the  iodine  contained 
in  it,  y the  chlorine  contained  in  it,  and  B the  amount  of  chloride 
and  iodide  of  silver  obtained : — 

x -f-  y — A,  and 
Ag  -f- 1 Ag  -4-  Cl 

1 x+ — a — y=£ 

Ag  + I 
— j — =1-851 

Ag  -f-  Cl 


B- 1-851  A 
y~  ¥'194: 

b.  If  you  have  free  iodine  and  free  chlorine  in  solution,  deter-  211 
mine  in  one  portion,  after  heating  with  sulphurous  acid,  the  iodine 
as  iodide  of  palladium  (§  145, 1.,  5),  and  treat  another  portion  as  di- 
rected § 146,  1.  Deduct  from  the  apparent  amount  of  iodine  found 
by  the  latter  process,  the  actual  quantity  calculated  from  the  iodide 


Now  as 


and 


we  have 


ACIDS  OF  GROUP  II. 


417 


§ 169.1 


of  palladium  ; the  difference  expresses  the  amount  of  iodine  equiva- 
lent to  the  chlorine  contained  in  the  substance. 


5.  Analysis  of  Bromine  containing  Chlorine. 


a.  Proceed  exactly  as  in  210,  weighing  the  bromine  in  a small  212 
glass  bulb.  Taking  A to  be  equal  to  the  analyzed  bromine,  1$  to 
the  bromide  and  chloride  of  silver  obtained,  x to  the  bromine  con- 
tained in  A,  y to  the  chlorine  contained  in  A,  the  calculation  is 
made  by  the  following  equations  : — 

x 4-  y = A 

and 


B - 2-35  A 

y = 

1-695 


b.  Mix  the  weighed  anhydrous  bromine  with  solution  of  iodide  213 
of  potassium  in  excess,  and  determine  the  separated  iodine  as  di- 
rected § 146. 

From  these  data,  the  respective  quantities  of  bromine  and  chlo- 
rine are  calculated  by  the  following  equations.  Let  A represent 
the  weighed  bromine,  i the  iodine  found,  y the  chlorine  contained 
in  A,  x the  bromine  contained  in  A , then 

x -h  y = A 
_i—  1-5866  A 

1-991 

Bunsen,  the  originator  of  methods  4 and  5,  has  experimentally 
proved  their  accuracy.* 

6.  Cyanogen  from  Chlorine,  Bromine,  or  Iodine. 

a.  Precipitate  with  solution  of  nitrate  of  silver,  collect  the  pre-  214 
cipitate  upon  a weighed  filter,  and  dry  in  the  water-bath  until  the 
weight  remains  constant ; then  determine  the  cyanogen  by  the 
method  of  organic  analysis ; the  difference  expresses  the  quantity 

of  the  chlorine,  bromine,  or  iodine. 

b.  Precipitate  with  solution  of  nitrate  of  silver  as  in  a , dry  the  215 
precipitate  at  100°,  and  weigh.  Heat  the  precipitate,  or  an  aliquot 
part  of  it,  in  a porcelain  crucible,  with  cautious  agitation  of  the 
contents,  to  complete  fusion ; add  dilute  sulphuric  acid  to  the  fused 
mass,  then  reduce  by  zinc,  filter  the  solution  from  the  metallic  silver 
and  paracyanide  of  silver,  and  determine  the  chlorine,  iodine,  or  bro- 
mine in  the  filtrate,  in  the  usual  way  by  solution  of  nitrate  of  silver. 

The  cyanide  of  silver  is  the  difference.  Neubauer  and  Kerner  \ 
obtained  very  satisfactory  results  by  this  method. 

c.  Determine  the  radicals  jointly  in  a portion  of  the  solution,  by  216 
precipitating  with  solution  of  nitrate  of  silver,  and  the  cyanogen  in 
another  portion,  in  the  volumetric  way  (§  147,  I.,  b). 

7.  Ferro-  or  Ferricyanogen  from  Hydrochloric  Acid. 

To  analyse  say  ferro-  or  ferricyanide  of  potassium,  mixed  with  217 
the  chloride  of  an  alkali  metal,  determine  in  one  portion  the  ferro-  or 
ferricyanogen  as  directed  § 147,  II.,  g ; acidify  another  portion  with 
nitric  acid,  precipitate  with  solution  of  nitrate  of  silver,  wash  the 

* Annal  d.  Chem.  u.  Pharm.  86,  274,  276.  f Ibid.  101,  344. 

27 


418 


SEPARATION. 


[§  170. 

precipitate,  fuse  with.  4 parts  of  carbonate  of  soda  and  1 part  of 
nitrate  of  potassa,  extract  the  fused  mass  with  water,  and  determine 
the  chlorine  in  the  solution  as  directed  in  § 141. 

8.  Sulphuretted  Hydrogen  from  Hydrochloric  Acid. 

The  old  method  of  separating  the  two  acids  by  means  of  a metallic  218 
salt  is  liable  to  give  false  results,  as  part  of  the  chloride  of  the  metal 
may  fall  down  with  the  sulphide.  We  therefore  precipitate  both  as 
silver  compounds,  dry  the  precipitate  at  100°,  and  determine  the 
sulphur  in  a weighed  portion  ; or — and  this  is  usually  preferred — 
determine  in  a portion  of  the  solution  the  sulphuretted  hydrogen  as 
directed  § 148, 1,  a , b,  or  c,  in  another  portion  the  sulphur  -f*  chlorine 
in  form  of  silver  salts.  If  you  employ  a solution  of  nitrate  of  silver 
mixed  with  excess  of  ammonia,  for  the  determination  of  the  sul- 
phuretted hydrogen,  you  may,  after  filtering  off  the  sulphide  of 
silver,  estimate  the  chlorine  directly  as  chloride  of  silver,  by  adding 
nitric  acid,  and,  if  necessary,  more  neutral  silver  solution.  To  remove 
sulphuretted  hydrogen  from* an  acid  solution,  in  order  that  chlorine 
may  be  determined  in  the  latter  by  means  of  nitrate  of  silver,  H. 
Rose  recommends  to  add  solution  of  sulphate  of  sesquioxide  of  iron, 
which  will  effect  the  separation  of  sulphur  alone ; the  separated 
sulphur  is  allowed  to  deposit,  and  then  filtered  off. 


third  group. 

Nitric  Acid — Chloric  Acid. 

I.  Separation  of  the  Acids  of  the  Third  Group  from  those  of 

THE  FIRST  TWO  GROUPS. 

§ 170. 

ci.  If  you  have  a mixture  of  nitric  acid  or  chloric  acid  with  219 
another  free  acid  in  a fluid  containing  no  bases,  determine  in  one 
portion  the  joint  amount  of  the  free  acid,  by  the  acidimetric  method 
(see  Special  Part),  in  another  portion  the  acid  mixed  with  the  chloric 
or  nitric  acid,  and  calculate  the  amount  of  either  of  the  latter  from 
the  difference. 

b.  If  you  have  to  analyze  a mixture  of  a nitrate  or  chlorate  with  220 
some  other  salt,  determine  in  one  portion  the  nitric  acid  or  chloric 
acid  volumetrically  (§  149,  II.,  c?,  a or  j 3,  or  II.,  e , and  § 150),  or 
the  nitric  acid  by  § 149,  II.,  a,  0 ; and  in  another  portion  the  other 
acid.  I think  I need  hardly  remark,  that  no  substances  must  be  pre- 
sent which  would  interfere  with  the  application  of  these  methods. 

c.  From  the  chlorides  of  those  metals  which  form  with  phosphoric  221 
acid  insoluble  tribasic  phosphates,  the  salts  of  the  acids  of  the  third 
group  may  be  separated  also  by  digesting  the  solution  with  recently 
precipitated  thoroughly  washed  tribasic  phosphate  of  silver  in  excess, 
and  boiling  the  mixture.  In  this  process  the  chlorides  transpose 
with  the  phosphate — chloride  of  silver  and  phosphate  of  the  metal 
with  which  the  chlorine  was  originally  combined  being  formed,  which 
both  separate,  together  with  the  excess  of  the  phosphate  of  silver, 


§ 570.] 


ACIDS  OF  GROUP  II. 


419 


whilst  the  chlorates  and  nitrates  remain  in  solution  (Chenevix  ; 
Lassaigne*). 

d . The  estimation  of  an  alkaline  chlorate,  in  presence  of  a chloride,  222 
may  be  effected  also  as  follows : — Take  two  portions  of  the  substance, 
determine  the  chlorine  by  means  of  silver  solution,  in  one  directly,  in 
the  other  after  reduction  of  the  chloric  acid  by  cautious  ignition  or 
by  nascent  hydrogen  (§  150,  II.,  c).  Calculate  the  chloric  acid  from 
the  difference  in  the  precipitates  of  chloride  of  silver. 

II.  Separation  of  the  Acids  of  the  Third  Group  from 
each  other. 

We  have  as  yet  no  method  to  effect  the  direct  separation  of  nitric  223 
acid  from  chloric  acid ; the  only  practicable  way,  therefore,  is  to 
determine  the  two  acids  jointly  in  a portion  of  the  compound,  by  the 
method  given  p.  330,  d,  measuring  the  sesquioxide  of  iron  remain- 
ing by  Oudeman’s  method  (p.  203),  and  bearing  in  mind  that  12 
eq.  of  iron,  converted  from  proto-  into  sesquichloride,  correspond  to 
1 eq.  of  chloric  acid.  In  another  portion  estimate  the  chloric  acid, 
by  adding  carbonate  of  soda  in  excess,  evaporating  to  dryness,  fus- 
ing the  residue  until  the  chlorate  is  completely  converted  into  chlo- 
ride, and  then  determining  the  chlorine  in  the  latter  ; 1 eq.  chloride 
of  silver  produced  from  this  corresponds  to  1 eq.  chloric  acid,  pro- 
vided there  was  no  chloride  originally  present. 


* Journ.  de  Phamu  16,  289  ; Pharxn.  Centralbl.  1850, 121. 


SECTION  VI. 


ORGANIC  ANALYSIS. 

§ 171. 

Organic  compounds  contain  comparatively  only  few  of  the  elements.  A 
small  number  of  them  consist  simply  of  2 elements,  viz., 

C and  H; 

the  greater  number  contain  3 elements,  viz.,  as  a rule, 

C,  H,  and  O ; 

most  of  the  rest  4 elements,  viz.,  generally, 

C,  H,  O,  and  N ; 
a small  number  5 elements,  viz., 

C,  H,  O,  N,  and  S ; 
and  a few,  6 elements,  viz., 

C,  H,  O,  N,  S,  and  P. 

This  applies  to  all  the  natural  organic  compounds  which  have  as  yet 
come  under  our  notice.  But  we  may  artificially  prepare  organic  com- 
pounds containing  other  elements  besides  those  enumerated ; thus  we 
know  many  organic  substances,  which  contain  chlorine,  iodine,  or  bro- 
mine ; others  which  contain  arsenic,  antimony,  tin,  zinc,  platinum,  iron, 
cobalt,  tfcc. ; and  it  is  quite  impossible  to  say  which  of  the  other  elements 
may  not  be  similarly  capable  of  becoming  more  remote  constituents  of 
organic  compounds  (constituents  of  organic  radicals). 

With  these  compounds  we  must  not  confound  those  in  which  organic 
acids  are  combined  with  inorganic  bases,  or  organic  bases  with  inorganic 
acids,  such  as  tartrate  of  lead,  for  instance,  silicic  ether,  borate  of 
morphia,  &c. ; since  in  such  bodies  any  of  the  elements  may  of  course 
occur. 

Organic  compounds  may  be  analyzed  either  with  a view  simply  to  re- 
solve them  into  their  proximate  constituents ; thus,  for  instance,  a gum- 
resin  into  resin,  gum,  and  ethereal  oil; — or  the  analysis  may  have  for  its 
object  the  determination  of  the  ultimate  constituents  (the  elements)  of  the 
substance.  The  simple  resolution  of  organic  compounds  into  their  prox- 
imate constituents  is  effected  by  methods  perfectly  similar  to  those  used  in 
the  analysis  of  inorganic  compounds  ; that  is,  the  operator  endeavors  to 
separate  (by  solvents,  application  of  heat,  &c.)  the  individual  constituents 
from  one  another,  either  directly,  or  after  having  converted  them  into 
appropriate  forms.  We  disregard  here  altogether  this  kind  of  organic 
analysis — of  which  the  methods  must  be  nearly  as  numerous  and  varied 
as  the  cases  to  which  they  are  applied — and  proceed  at  once  to  treat 
of  the  second  kind,  which  may  be  called  the  ultimate  analysis  of  organic 
bodies. 

The  ultimate  analysis  of  organic  bodies  ( here  termed  simply , organic 
analysis ) has  for  its  object,  as  stated  above,  the  determination  of  the 


171,  172.] 


ORGANIC  ANALYSIS. 


421 


elements  contained  in  organic  substances.  It  teaches  us  bow  to  isolate 
these  elements  or  to  convert  them  into  compounds  of  known  composition, 
to  separate  the  new  compounds  formed  from  one  another,  and  to  calculate 
from  their  several  weights,  or  volumes,  the  quantities  of  the  elements. 
Organic  analysis,  therefore,  is  based  upon  the  same  principle  upon  which 
rest  most  of  the  methods  of  separating  and  determining  inorganic  com- 
pounds. 

The  conversion  of  most  organic  substances  into  distinctly  characterized 
and  readily  separable  products,  the  weights  of  which  can  be  accurately 
determined,  offers  no  great  difficulties,  and  organic  analysis  is  therefore 
usually  one  of  the  more  easy  tasks  of  analytical  chemistry; — and  as,  from 
the  limited  number  of  the  elements  which  constitute  organic  bodies,  there 
is  necessarily  a great  sameness  in  the  products  of  their  decomposition,  the 
analytical  process  is  always  very  similar,  and  a few  methods  suffice  for  all 
cases.  It  is  principally  ascribable  to  this  latter  circumstance  that  organic 
analysis  has  so  speedily  attained  its  present  high  degree  of  perfection  : — 
the  constant  examination  and  improvement  of  a few  methods  by  a great 
number  of  chemists  could  not  fail  to  produce  this  result. 

An  organic  analysis  may  have  for  its  object  either  simply  to  ascertain 
the  relative  quantities  of  the  constituent  elements  of  a substance, — thus, 
for  instance,  woods  may  be  analyzed  to  ascertain  their  heating  power,  fats 
to  ascertain  their  illuminating  power, — or  to  determine  not  only  the  rela- 
tive quantities  of  the  constituent  elementary  atoms,  but  also  their  abso- 
lute quantities,  that  is,  to  determine  the  number  of  equivalents  of  carbon, 
hydrogen,  oxygen,  &c.,  which  constitute  1 equivalent  of  the  analyzed  com- 
pound. In  scientific  investigations  we  have  invariably  the  latter  object 
in  view,  although  we  are  not  yet  able  to  achieve  it  in  all  cases.  These 
two  objects  cannot  well  be  attained  by  one  operation ; each  requires  a 
distinct  process. 

The  methods  by  which  we  ascertain  the  proportions  of  the  constituent 
elements  of  organic  compounds,  may  be  called  collectively,  the  ultimate 
analysis  of  organic  bodies , in  a more  restricted  sense ; whilst  the  methods 
which  reveal  to  us  the  absolute  number  of  elementary  equivalents  con- 
stituting the  complex  equivalent  of  the  analyzed  compound  may  be  styled 
the  determination  of  the  equivalents  of  organic  bodies. 

The  success  of  an  organic  analysis  depends  both  upon  the  method  and 
its  execution.  The  latter  requires  patience,  circumspection,  and  skill ; 
whoever  is  moderately  endowed  with  these  gifts  will  soon  become  a pro- 
ficient in  this  branch.  The  selection  of  the  method  depends  upon  the 
knowledge  of  the  constituents  of  the  substance,  and  the  method  selected 
may  require  certain  modifications,  according  to  the  properties  and  state 
of  aggregation  of  the  same.  Before  we  can  proceed,  therefore,  to  describe 
the  various  methods  applicable  in  the  different  cases  that  may  occur,  we 
have  first  to  occupy  ourselves  here  with  the  means  of  testing  organic 
bodies  qualitatively. 

I.  Qualitative  Examination  of  Organic  Bodies. 

§172. 

It  is  not  necessary  for  the  correct  selection  of  the  proper  method,  tc 
know  all  the  elements  of  an  organic  compound,  since,  for  instance,  the 
presence  or  absence  of  oxygen  makes  not  the  slightest  difference  to  the 


422 


ORGANIC  ANALYSIS. 


method.  But  with  regard  to  other  elements,  such  as  nitrogen,  sulphur, 
phosphorus,  chlorine,  iodine,  bromine,  &c.,  and  also  the  various  metals, 
it  is  absolutely  indispensable  that  the  operator  should  know  positively 
whether  either  of  them  is  present.  This  may  be  ascertained  in  the  fol- 
lowing manner : — 

1.  Testing  for  Nitrogen . 

Substances  containing  a tolerably  large  amount  of  nitrogen  exhale 
upon  combustion,  or  when  intensely  heated,  the  well-known  smell  of 
singed  hair  or  feathers.  No  further  test  is  required  if  this  smell  is  dis- 
tinctly perceptible ; otherwise  one  of  the  following  experiments  is  resorted 
to : — 

a.  The  substance  is  mixed  with  hydrate  of  potassa  in  powder  or  with 
soda-lime  (§  66,  4),  and  the  mixture  heated  in  a test-tube.  If  the  sub- 
stance contains  nitrogen,  ammonia  will  be  evolved,  which  may  be  readily 
detected  by  its  odor  and  reaction,  and  by  the  formation  of  white  fumes 
with  volatile  acids.  Should  these  reactions  fail  to  afford  positive  certainty, 
every  doubt  may  be  removed  by  the  following  experiment : — Heat  a some- 
what larger  portion  of  the  substance,  in  a short  tube,  with  an  excess  of  soda- 
lime,  and  conduct  the  products  of  the  combustion  into  dilute  hydrochloric 
acid ; evaporate  the  acid  on  the  water-bath,  dissolve  the  residue  in  a little 
water,  and  mix  the  solution  with  bichloride  of  platinum  and  alcohol. 
Should  no  precipitate  form,  even  after  the  lapse  of  some  time,  the  substance 
may  be  considered  free  from  nitrogen. 

b.  Lassaigne  has  proposed  another  method,  which  is  based  upon  the 
property  of  potassium  to  form  cyanide  of  potassium  when  ignited  with  a 
nitrogenous  organic  substance.  The  following  is  the  best  mode  of  per- 
forming the  experiment : — 

Heat  the  substance  under  examination,  in  a test-tube,  with  a small 
lump  of  potassium,  and  after  the  complete  combustion  of  the  potassium, 
treat  the  residue  with  a little  water  (cautiously)  ; filter  the  solution,  add  2 
drops  of  solution  of  sulphate  of  protoxide  of  iron  containing  some  sesqui- 
oxide,  digest  the  mixture  a short  time,  and  add  hydrochloric  acid  in  excess. 
The  formation  of  a blue  or  bluish-green  precipitate  or  coloration  proves 
the  presence  of  nitrogen. 

Both  methods  are  delicate  : a is  the  more  commonly  employed,  and 
suffices  in  almost  all  cases ; b does  not  answer  so  well  in  the  case  of  alkaloids 
containing  oxygen  ( e.g . morphia,  brucia). 

c.  In  organic  substances  containing  oxides  of  nitrogen,  the  presence  of 
nitrogen  cannot  be  detected  with  certainty  bv  either  a or  b,  but  it  may  be 
readily  discovered  by  heating  the  substance  in  a tube,  when  red  acid 
fumes,  imparting  a blue  tint  to  iodide  of  starch  paper,  will  be  evolved, 
accompanied  often  by  deflagration. 

2.  Testing  for  Sulphur. 

a.  Solid  substances  are  fused  with  about  1 2 parts  of  pure  hydrate  of 
potassa,  and  six  parts  of  nitrate  of  potassa.  Or  they  are  intimately  mixed 
with  some  pure  nitrate  of  potassa  and  carbonate  of  soda ; nitrate  of  potassa 
is  then  heated  to  fusion  in  a porcelain  crucible,  and  the  mixture  gradually 
added  to  the  fusing  mass.  The  mass  is  allowed  to  cool,  then  dissolved  in 
water,  and  the  solution  tested  with  baryta,  after  acidifying  with  hydro- 
chloric acid. 


§ 173.] 


ORGANIC  ANALYSIS. 


423 


b.  Fluids  are  treated  with  fuming  nitric  acid,  or  with  a mixture  of  nitric 
acid  and  chlorate  of  potassa,  at  first  in  the  cold,  finally  with  application 
of  heat ; the  solution  is  tested  as  in  a. 

c.  As  the  methods  a and  b serve  simply  to  indicate  the  presence  of  sul- 
phur in  a general  way,  but  afford  no  information  regarding  the  state  or 
form  in  which  that'  element  may  be  present,  I add  here  another  method, 
which  serves  to  detect  only  the  sulphur  in  the  non-oxidized  state  in  organic 
compounds. 

Boil  the  substance  with  strong  solution  of  potassa  and  evaporate  nearly 
to  dryness.  Dissolve  the  residue  in  a little  water,  and  test  by  means  of 
a polished  surface  of  silver,  or  by  nitroprusside  of  sodium,  or  by  just  acidi- 
fying the  dilute  solution  with  hydrochloric  acid,  and  adding  a few  drops 
of  a mixture  of  sesquichloride  of  iron  and  ferricyanide  of  potassium  (see 
“ Qual  Anal.”  § 156). 

3.  Testing  for  Phosphorus. 

The  methods  described  in  2,  a and  6,  may  likewise  serve  for  phos- 
phorus. The  solutions  obtained  are  tested  for  phosphoric  acid  with 
sulphate  of  magnesia  ; or  with  sesquichloride  of  iron,  with  addition  of 
acetate  of  soda ; or  with  molybdate  of  ammonia  (comp.  “ Qual.  Anal.”). 
In  method  b , the  greater  part  of  the  excess  of  nitric  acid  must  first  be 
removed  by  evaporation. 

4.  Testing  for  Inorganic  Sabstances. 

A portion  of  the  substance  is  heated  on  platinum  foil,  to  see  whether  or 
not  a residue  remains.  When  acting  upon  difficultly  combustible  sub- 
stances, the  process  may  be  accelerated  by  heating  the  spot  which  the  sub- 
stance occupies  on  the  platinum  foil  to  the  most  intense  redness,  by 
directing  the  flame  of  the  blow-pipe  upon  it  from  below.  The  residue  is 
then  examined  by  the  usual  methods.  That  volatile  metals  in  volatile 
organic  compounds — e.g .,  arsenic  in  kakodyl — cannot  be  detected  by  this 
method,  need  hardly  be  mentioned. 

These  preliminary  experiments  should  never  be  omitted,  since  neglect  in 
this  respect  may  give  rise  to  very  great  errors.  Thus,  for  instance,  taurin, 
a substance  in  which  a large  proportion  of  sulphur  was  afterwards  found 
to  exist,  had  originally  the  formula  C4  1ST  II7  O10  assigned  to  it.  The  pre- 
liminary examination  of  organic  substances  for  chlorine,  bromine,  and 
iodine  is  generally  unnecessary,  as  these  elements  do  not  occur  in  natiye 
organic  compounds  ; and  as  their  presence  in  compounds  artificially  pro- 
duced by  the  action  of  the  halogens  requires  generally  no  further  proof. 
Should  it,  however,  be  desirable  to  ascertain  positively  whether  a sub- 
stance does  or  does  not  contain  chlorine,  iodine,  or  bromine,  this  may  be 
done  by  the  methods  given  § 188. 

II.  Determination  of  the  Elements  in  Organic  Bodies.* 

§ 173. 

A.  Analysis  of  Compounds  which  consist  simply  of  Carbon  and 
Hydrogen,  or  of  Carbon,  Hydrogen,  and  Oxygen. 

The  principle  of  the  method  which  serves  to  effect  the  quantitative 
analysis  of  such  compounds  is  exceedingly  simple.  The  substance  is 


[*  For  Prof.  Warren’s  admirable  methods  we  must  refer  to  his  original  papers  in 
Am.  Joum.  Sci.,  2dser.,  tol.  38,  p.  387,  vol.  41,  p.  40,  and  vol.  42,  p.  156.] 


424 


ORGANIC  ANALYSIS. 


burned  to  carbonic  acid  and  water ; these  products  are  separated  from 
each  other  and  weighed,  and  the  carbon  of  the  substance  is  calculated 
from  the  weight  of  the  carbonic  acid,  the  hydrogen  from  that  of  the  water. 
If  the  sum  of  the  carbon  and  hydrogen  is  equal  to  the  original  weight 
of  the  substance,  the  substance  contains  no  oxygen  ; if  it  is  less  than  the 
weight  of  the  substance,  the  difference  expresses  the  amount  of  oxygen 
present. 

The  combustion  is  effected  either  by  igniting  the  organic  substance 
with  oxygenized  bodies  which  readily  part  with  their  oxygen  (oxide  of 
copper,  chromate  of  lead,  &c.) ; or  at  the  expense  both  of  free  and  com- 
bined oxygen. 

a.  Solid  Bodies. 

Combustion  with  Oxide  of  Copper. 

§174. 

I.  Apparatus  and  Preparations  required  for  the  Analysis. 

1.  The  Substance. — This  must  be  most  finely  pulverized  and  perfectly 
pure  and  dry  ; — for  the  method  of  drying,  I refer  to  § 26. 

2.  A Tube  in  which  to  weigh  the  Substance,  made  of  thin  glass 
about  20  cm.  long,  and  of  7 mm.  internal  diameter ; one  end  of  the  tube 
is  closed  by  fusion  ; the  other,  during  the  operation  of  weighing,  is  stop- 
ped with  a smooth  cork. 

3.  The  Combustion  Tube. — A tube  of  difficultly  fusible  glass  (potassa 
glass),  about  2 mm.  thick  in  the  glass,  80  to  90  cm.  in  length,  and  from 
12  to  14  mm.  inner  diameter,  is  softened  in  the  middle  before  a glass- 
blower’s  lamp,  drawn  out  as  represented  in  fig.  69,  and  finally  apart  at 


Fig.  69. 


b.  The  fine  points  of  the  two  pieces  are  then  sealed  and  thickened  a lit- 
tle in  the  flame,  and  the  sharp  edges  of  the  open  ends,  a and  c,  are 
slightly  rounded  by  fusion,  care  being  taken  to  leave  the  aperture  per- 
fectly round.  The  posterior  part  of  the  tube  should  be  shaped  as  shown 
in  fig.  70,  and  not  as  in  fig.  71. 


Fig.  70. 


Fig.  71. 


Two  perfect  combustion  tubes  are  thus  produced.  The  one  intended 
for  immediate  use  is  cleaned  with  linen  or  paper  attached  to  a piece  of 
wire,  and  then  thoroughly  dried.  This  is  effected  either  by  laying  the  tube, 
with  a piece  of  paper  twisted  over  its  mouth,  for  some  time  on  a sand- 


174.] 


ORGANIC  ANALYSIS. 


425 


bath,  with  occasional  removal  of  the  air  from  it  by  suction,  with  the  aid 
of  a glass  tube,  or  (rapidly)  by  moving  the  tube  to  and  fro  over  the 
flame  of  a gas  or  spirit  lamp,  heating  its  entire  length,  and  continually 
removing  the  hot  air  by  suction  through  the  small  glass  tube  (fig.  72). 


The  combustion  tube,  when  quite  dry,  is  closed  air-tight  with  a cork, 
and  kept  in  a warm  place  until  required  for  use. 

In  default  of  glass  tubes  possessed  of  the  proper  degree  of  infusibility, 
thin  brass  or  copper  foil,  or  brass  gauze,  is  rolled  round  the  tube,  and 
iron  wire  coiled  round  it. 

4.  The  Potash-bulbs  (fig.  73). — This  apparatus,  devised  by  Liebig, 
is  filled  to  the  extent  indicated  in  the  en- 
graving, with  a clear  solution  of  caustic  po- 
tassa  of  1*27  sp.  gr.  (§  66,  6).  The  introduc- 
tion of  the  solution  of  potassa  into  the  appara- 
tus is  effected  by  plunging  the  end  a into  a 
beaker  or  dish  into  which  a little  of  the  solu- 
tion has  been  poured  out,  and  applying  suction 
to  b , by  means  of  a caoutchouc  tube.  The  two 
ends  are  then  wiped  perfectly  dry  with  twisted 
slips  of  paper,  and  the  outside  of  the  appara- 
tus with  a clean  cloth. 

5.  The  Chloride-of-Calcium-tube  (fig.  7 4) 
is  filled  in  the  following  manner : — In  the  first 
place,  the  neck  between  the  two  bulbs  of  the 
tube  is  loosely  stopped  with  a small  cotton  plug ; this  is  effected  by  in- 
troducing a loose  cotton  plug  into  the  wide  tube,  and  applying  a sudden 
and  energetic  suction  at  the  other  end.  The  large  bulb  is  then  filled 
with  lumps  of  chloride  of  calcium  (§  66,  7,  6),  and  the  tube  with  smaller 
fragments,  intermixed  with  coarse  powder  of  the  same  substance  ; a loose 
cotton  plug  is  then  inserted,  and  the  tube  finally  closed  with  a perfo- 
rated cork,  into  which  a small  glass  tube  is  fitted ; the  protruding  part 
of  the  cork  is  cut  off,  and  the  cut  surface  covered  over  with  sealing-wax  • 
the  edge  of  the  little  tube  is  slightly  rounded  by  fusion. 

In  using  this  tube  a considerable  quantity  of  the  water  condenses  in 


Fig.  74. 


the  empty  bulb  a,  and  at  the  close  of  the  experiment  may  be  poured  out 
The  operator  is  thus  enabled  to  test  it  as  to  reaction,  &c.,  and  also  to  use 
the  same  tube  far  oftener  without  fresh  filling  than  he  could  other- 
wise. 


426 


ORGANIC  ANALYSIS. 


L§  174. 


6.  A Small  Tube  of  vulcanized  India-rubber. — This  must  be  so 
narrow  that  it  can  only  be  pushed  with  difficulty  over  the  tube  of  the 
chloride  of  calcium  tube  on  the  one  hand,  and  over  the  end  of  the 
potash  bulbs  on  the  other  hand ; in  which  case  there  is  no  need  of  bind- 
ing with  silk  cord.  If  the  rubber  tube  should  be  a little  too  wide,  it 
must  be  tied  round  with  silk  cord,  or  with  ignited  piano  wire.  It  is 
self-evident  that  the  narrow  end  of  the  chloride  of  calcium  tube  should 
be  of  the  same  width  as  the  tube  a of  the  potash  bulbs.  The  india-rub- 
ber tube  is  purified  from  any  adherent  sulphur,  and  dried  in  the  water- 
bath  previous  to  use. 

7.  Corks. — These  should  be  soft  and  smooth,  and  as  free  as  possible 
from  visible  pores.  A cork  should  be  selected  which,  after  careful 
squeezing,  fits  perfectly  tight,  and  screws  with  some  difficulty  to  one- 
third  of  its  length,  at  the  most,  into  the  mouth  of  the  combustion-tube ; 
a perfectly  smooth  and  round  hole,  into  which  the  end  a of  the  chloride 
of  calcium  tube  must  fit  perfectly  air-tight,  is  then  carefully  bored 
through  the  axis  of  the  cork.  The  cork  is  then  kept  for  an  hour  or  two 
in  the  water  bath.  It  is  advisable  always  to  have  two  corks  of  this 
description  ready.  Instead  of  ordinary  corks,  caoutchouc  stoppers  may 
be  used  with  great  advantage. 

8.  Oxide  of  Copper. — A Hessian  crucible,  of  about  100  c.  c.  capacity, 

is  nearly  filled  with  oxide  of  copper  prepared  as  directed  in 
§ 66,  1 ; the  crucible  is  covered  with  a well-fitting  overlap- 
ping lid,  and  heated  to  dull  redness  with  charcoal,  or  in  a 
suitable  gas-furnace  ; it  is  then  allowed  to  cool,  so  that  by 
the  time  the  oxide  of  copper  is  required  for  use,  the  hand  can 
only  just  bear  contact  with  it. 

9.  A wide  glass  Tube  sealed  at  one  end,  or  a Flask 
(fig.  75),  in  which  the  freshly  ignited  oxide  of  copper  is  al- 
lowed to  cool,  and  from  which  it  is  transferred  to  the  combus- 
tion tube,  secure  from  the  possible  absorption  of  moisture 
from  the  air. 

The  freshly  ignited  and  still  quite  hot  oxide  of  copper  is 
Fig.  75.  transferred  direct  from  the  crucible  to  this  filling  tube,  or 
flask,  which  is  then  closed  air-tight  with  a cork.  It  saves  time  to  fill  in 
at  once  a sufficient  quantity  of  oxide  to  last  for  several  analyses.  If  the 
cork  fits  tight,  the  contents  will  remain  several  days  fit  for  use,  even 
though  a portion  has  been  taken  out,  and  the  tube  repeatedly  opened. 

10.  A Mixing  Wire  of  copper  (fig.  76)  with  ring  at  one  end  for  a 


Fig.  76. 


handle,  and  a single  corkscrew  turn  at  the  other,  which  should  taper 


smoothly  to  a point. 


Fig.  77. 


11.  A Combustion-furnace. — 
Some  time  ago  the  only  one  used  was 
Liebig’s,  in  which  charcoal  is  the  fuel. 
Recently  gas  combustion  furnaces 
have  been  introduced  into  most  la- 
boratories, because  they  are  more 
cleanly  and  convenient. 


175.] 


ORGANIC  ANALYSIS. 


427 


a.  Liebig’s  combustion  furnace  is  of  sheet  iron.  It  has  the  form  of  a 
long  box,  open  at  the  top  and  behind.  It  serves  to  heat  the  combus- 
tion tube  with  red-hot  charcoal.  Fig.  77  represents  the  furnace  as  seen 
from  the  top. 

It  is  from  50  to  60  cm.  long,  and  from  7 to  8 deep  ; the  bottom,  which, 
by  cutting  small  slits  in  the  sheet  iron,  is  converted  into  a grating,  has 
a width  of  about  7 cm.  The  side  walls  are  inclined  slightly  outward,  so 
that  at  the  top  they  stand  about  12  cm.  apart.  A series  of  upright 
pieces  of  strong  sheet  iron,  having  the  form  shown  in  D , fig.  78,  and 
riveted  on  the  bottom  of  the  furnace  at  intervals  of  about  5 cm., 
serves  to  support  the  combustion  tube.  They  must  be  of  exactly  cor- 
responding height  with  the  round  aperture  in  the  front  piece  of  the  fur- 
nace (fig.  78,  A). 


Fig.  78.  Fig.  79. 

This  aperture  must  be  sufficiently  large  to  admit  the  combustion  tube 
easily.  Of  the  two  screens,  the  one  has  the  form  shown  in  fig.  79,  the 
other  that  shown  in  fig.  78,  A,  with  the  border  turned  down  at  the  up- 
per edge.  The  openings  cut  into  the  screens  must  be  sufficiently  large 
to  receive  the  combustion  tube  without  difficulty.  The  furnace  is  placed 
upon  two  bricks  resting  upon  a flat  surface,  and  is  slightly  raised  at  the 
farther  end,  by  inserting  a piece  of  wood  between  the  supports  (see 
fig.  82).  The  apertures  of  the  grating  at  the  anterior  end  of  the  furnace 
must  not  be  blocked  up  by  the  supporting  bricks.  In  cases  where  the 
combustion  tubes  are  of  a good  quality,  the  furnace  may  be  raised  by  in- 
troducing a little  iron  rod  between  the  furnace  and  the  supporting 
brick.  Placing  the  tube  in  a gutter  of  Russia  sheet  iron  tends  greatly  to 
preserve  it,  but  contact  of  the  glass  and  iron  must  be  prevented  by  an 
intervening  layer  of  asbestos. 

b.  Gas  combustion  furnaces  of  the  most  various  descriptions  have  been 
proposed.  See  § 178. 

§ U5. 

II.  Performance  of  the  Analytical  Process. 

a.  Weigh  first  the  potash  apparatus,  then  the  chloride  of  calcium  tube. 
Introduce  about  035 — 0'6  grm.  of  the  substance  under  examination 
(more  or  less,  according  as  it  is  rich  or  poor  in  oxygen)  into  the 
weighing  tube,*  which  must  be  no  longer  warm,  and  weigh  the  latter 
accurately  with  its  contents.  The  weight  of  the  empty  tube  being  ap- 
proximately known,  it  is  easy  to  take  the  right  quantity  of  substance  re- 
quired for  the  analysis.  Close  the  tube  then  with  a smooth  cork. 

b.  The  filling  of  the  combustion  tube  is  effected  as  follows  : — The  per- 
fectly dry  tube  is  rinsed  with  some  oxide  of  copper  ; a layer  of  oxide  of 
copper,  about  13  cm.  long,  is  introduced  into  the  posterior  end  of  the 
combustion  tube,  by  inserting  the  latter  into  the  filling  tube  or  flask 


* Care  must  be  taken  that  no  particles  of  the  substance  adhere  to  the  sides  of 
the  tube,  at  least  not  at  the  top. 


428 


ORGANIC  ANALYSIS. 


containing  the  oxide  of  copper  (fig.  80),  holding  both  tubes  in  an  ob- 
lique direction,  and  giving  a few  gentle  taps. 


Fig.  80. 


From  the  tube  containing  the  substance  remove  the  cork  cautiously, 
to  prevent  the  slightest  loss  of  substance  ; insert  the  open  end  of  the  tube 
as  deep  as  possible  into  the  combustion  tube,  and  pour  from  it  the  requi- 
site quantity  of  substance  by  giving  it  a few  turns,  pressing  the  rim  all 
the  while  gently  against  the  upper  side  of  the  combustion  tube,  to  pre- 
vent its  coming  into  contact  with  the  powder  already  poured  out  ; the 
two  tubes  are,  in  this  manipulation,  held  slightly  inclined  (see  fig.  81). 


Fig.  81. 


When  a sufficient  quantity  of  the  substance  has  been  thus  transferred 
from  the  weighing  to  the  combustion  tube,  the  latter  is  restored  to  the 
horizontal  position,  which  gives  to  the  former  a gentle  inclination  with 
the  closed  end  downwards.  If  the  little  tube  is  now  slowly  withdrawn, 
with  a few  turns,  the  powder  near  the  border  of  the  opening  falls  back 
into  it,  leaving  the  opening  free  for  the  cork.  The  tube  is  then  imme- 
diately corked  and  weighed,  the  combustion  tube  also  being  meanwhile 
kept  closed  with  a cork.  The  difference  between  the  two  weighings 
shows  the  quantity  of  substance  transferred  from  the  weighing  to  the 
combustion  tube.  The  latter  is  then  again  opened,  and  a quantity  of 
oxide  of  copper,  equal  to  the  first,  transferred  to  it  from  the  filling  tube, 
or  flask,  taking  care  to  rinse  down  with  this  the  particles  of  the  sub- 
stance still  adhering  to  the  sides  of  the  tube.  There  is  now  in  the  hind 
part  of  the  tube  a layer  of  oxide  of  copper,  about  25  cm.  long,  with  the 
substance  in  the  middle. 

The  next  operation  is  the  mixing : this  is  performed  with  the  aid  of 
the  wire  (fig.  76),  which  is  pushed  down  to  within  3 to  4 cm.  of  the  end, 
and  rapidly  moved  about  in  all  directions  until  the  mixture  is  complete 
and  uniform,  the  tube  being  held  nearly  horizontal. 

Oxide  of  copper  is  then  poured  in  to  within  5 to  6 cm.  of  the  open 
end,  and  the  tube  is  corked. 

c.  A few  gentle  taps  on  the  table  will  generally  suffice  to  shake  to- 
gether the  contents  of  the  tube,  so  as  to  completely  clear  the  tail  from 
oxide  of  copper,  and  leave  a free  passage  for  the  evolved  gases  from  end 
to  end.  Should  this  fail,  as  will  occasionally  happen,  owing  to  mal- 
formation of  the  tail,  the  object  in  view  may  be  attained  by  striking  the 
mouth  of  the  tube  several  times  against  the  side  of  a table. 

d.  Connect  the  end  b (fig.  82)  of  the  weighed  chloride  of  calcium 
tube  with  the  combustion  tube  by  means  of  a dried  perforated  cork,  lay 


ORGANIC  ANALYSIS. 


429 


§ 175.J 

the  furnace  upon  its  supports,  with  a slight  inclination  forward,  and 
place  the  combustion  tube  in  it ; connect  the  end  B of  the  chloride  of 
calcium  tube,  by  means  of  a vulcanized  india-rubber  tube,  with  the  end 
m of  the  potash  apparatus,  and,  if  necessary,  secure  the  connection  with 
silk  cord,  taking  care  to  press  the  joint  of  the  two  thumbs  close  together 
whilst  tightening  the  cords,  since  otherwise,  should  one  of  the  cords  hap- 
pen to  give  way,  the  whole  apparatus  might  be  broken.  Best  the  potash 
apparatus  upon  a folded  piece  of  cloth.  Fig.  82  shows  the  whole  ar- 
rangement. 


B 


Fig.  82. 

e.  To  ascertain  whether  the  joinings  of  the  apparatus  fit  air-tight,  put 
a piece  of  wood  about  the  thickness  of  a finger  (s),  or  a cork  or  other 
body  of  the  kind,  under  the  bulb  r of  the  potash  apparatus,  so  as  to 
raise  that  bulb  slightly  (see  fig.  82).  Heat  the  bulb  m , by  holding  a 
piece  of  red-hot  charcoal  near  it,  until  a certain  amount  of  air  is  driven 
out  of  the  apparatus ; then  remove  the  piece  of  wood  (s),  and  allow  the 
bulb  m to  cool.  The  solution  of  potassa  will  now  rise  into  the  bulb  m , 
filling  it  more  or  less ; if  the  liquid  in  m preserves,  for  the  space  of  a 
few  minutes,  the  same  level  which  it  has  assumed  after  the  perfect  cool- 
ing of  the  bulb,  the  joinings  may  be  considered  perfect ; should  the  fluid, 
on  the  other  hand,  gradually  regain  its  original  level  in  both  limbs  of 
the  apparatus,  this  is  a positive  proof  that  the  joinings  are  not  air-tight. 
(The  few  minutes  which  elapse  between  the  two  observations  may  be 
advantageously  employed  in  reweighing  the  little  tube  in  which  the  sub- 
stance intended  for  analysis  was  originally  weighed.) 

f.  Let  the  mouth  of  the  combustion  tube  project  a full  inch  beyond 
the  furnace  ; suspend  the  single  screen  over  the  anterior  end  of  the  fur- 
nace, as  a protection  to  the  cork  ; put  the  double  screen  over  the  com- 
bustion tube  about  two  inches  farther  on  (see  fig.  82),  replace  the  little 
piece  of  wood  ( s ) under  r,  and  put  small  pieces  of  red-hot  charcoal  first 
under  that  portion  of  the  tube  which  is  separated  by  the  screen  ; sur- 
round this  portion  gradually  altogether  with  ignited  charcoal,  and  let  it 
get  red-hot ; then  shift  the  screen  an  inch  farther  back,  surround  the 
newly  exposed  portion  of  the  tube  also  with  ignited  charcoal,  and  let  it 
get  red-hot ; and  proceed  in  this  manner  slowly  and  gradually  extend- 
ing the  application  of  heat  to  the  tail  of  the  tube,  taking  care  to  wait 
always  until  the  last  exposed  portion  is  red-hot  before  shifting  the 
screen,  and  also  to  maintain  the  whole  of  the  exposed  portion  of  the 
tube  before  the  screen  in  a state  of  ignition,  and  the  projecting  part  of 
it  so  hot  that  the  fingers  can  hardly  bear  the  shortest  contact  with  it. 
The  whole  process  requires  generally  from  f to  1 hour.  It  is  quite  su- 
perfluous, and  even  injudicious,  to  fan  the  charcoal  constantly ; — this 
should  be  done  however  when  the  process  is  drawing  to  an  end,  as  we 
shall  immediately  have  occasion  to  notice. 


430 


ORGANIC  ANALYSIS. 


L§  175. 


The  liquid  in  the  potash  bulbs  is  gradully  displaced  from  the  bulb  m 
upon  the  application  of  heat  to  the  anterior  portion  of  the  combustion 
tube,  owing  simply  to  the  expansion  of  the  heated  air.  The  evolution 
of  gas  proceeds  with  greater  briskness  when  the  heat  begins  to  reach 
the  actual  mixture ; the  first  bubbles  are  only  partly  absorbed,  as  the 
carbonic  acid  contains  still  an  admixture  of  air  ; but  those  which  follow 
are  so  completely  absorbed  by  the  potassa,  that  a solitary  air-bubble  only 
from  time  to  time  through  the  liquid.  The  process  should  be 
conducted  in  a manner  to  make  the  gas-bub- 
bles follow  each  other  at  intervals  of  from  ^ 
to  1 second.  Fig.  83  shows  the  proper  posi- 
tion of  the  potash  bulbs  during  the  opera- 
tion. 

It  will  be  seen  from  this  that  an  air-bubble 
entering  through  m passes  first  into  the  bulb 
b,  thence  to  c,  from  c to  d , and  passing  over 
the  solution  in  the  latter,  escapes  finally  into 
the  bulb  f,  through  the  fluid  which  just  covers 
the  mouth  of  the  tube  e. 

g.  When  the  tube  is  in  its  whole  length 


Fig.  83. 


surrounded  with  red-hot  charcoal,  and  the 
evolution  of  gas  has  relaxed,  fan  the  burning 
charcoal  gently  with  a piece  of  pasteboard.  When  the  evolution  of  gas 
has  entirely  ceased,  adjust  the  position  of  the  potash  bulbs  to  a level, 
remove  the  charcoal  from  the  farther  end  of  the  tube,  and  place  the 
screen  before  the  tail.  The  ensuing  cooling  of  the  tube  on  the  one  hand, 
and  the  absorption  of  the  carbonic  acid  in  the  potash  bulbs  on  the  other, 
cause  the  solution  of  potassa  in  the  latter  to  recede,  slowly  at  first,  but 
with  increased  rapidity  from  the  moment  the  liquid  reaches  the  bulb  m. 
(If  you  have  taken  care  to  adjust  the  position  of  the  potash  bulbs  cor- 
rectly, you  need  not  fear  that  the  contents  of  the  latter  will  recede  to 
the  chloride  of  calcium  tube.)  When  the  bulb  m is  about  half  filled 
with  solution  of  potassa,  break  off  the  point  of  the  combustion  tube  with 
a pair  of  pliers  or  scissors,  whereupon  the  fluid  in  the  potash  bulbs  will 
immediately  resume  its  level.  Restore  the  potash  bulbs  now  again  to 
their  original  oblique  positron,  join  a caoutchouc  tube  to  the  potash 
bulbs,  and  slowly  apply  suction  until  the  last  bubbles  no  longer  diminish 
in  size  in  passing  through  the  latter.  It  is  better  to  employ  a small 
aspirator  instead  of  sucking  with  the  mouth.  You  then  know  the 
volume  of  air  that  has  passed  through  the  apparatus. 

This  terminates  the  analytical  process.  Disconnect  the  potash  bulbs 
and  remove  the  chloride  of  calcium  tube,  together  with  the  cork,  which 
must  not  be  charred,  from  the  combustion  tube  ; remove  the  cork  also 
from  the  chloride  of  calcium  tube,  and  place  the  latter  upright,  with 
the  bulb  upwards.  After  the  lapse  of  half  an  hour,  weigh  the  potash  bulbs 
and  the  chloride  of  calcium  tube,  and  then  calculate  the  results  obtained. 
They  are  generally  very  satisfactory.  As  regards  the  carbon,  they  are 
rather  somewhat  too  low  (about  0T  per  cent.)  than  too  high.  The  car- 
bon determination,  indeed,  is  not  free  from  sources  of  error;  but  none 
of  these  interfere  materially  with  the  accuracy  of  the  results,  and  the 
deficiency  arising  from  the  one  is  partially  balanced  by  the  excess  aris- 
ing from  the  other.  In  the  first  place,  the  air  which  passes  through 
the  solution  of  potassa  during  the  combustion,  and  finally  during  the 


ORGANIC  ANALYSIS. 


431 


§§  176,  177.1 

process  of  suction,  carries  away  with  it  a minute  amount  of  moisture. 
The  loss  arising  from  this  cause  is  increased  if  the  evolution  of  gas  pro- 
ceeds very  briskly,  since  this  tends  to  heat  the  solution  of  potassa  ; and 
also  if  nitrogen  or  oxygen  passes  through  the  potash  bulbs  (compare 
§176  and  § 178).  This  may  be  remedied,  however,  by  fixing  to  the 
exit  end  of  the  latter  a tube  with  solid  hydrate  of  potassa  or  soda-lime, 
the  bulbs  and  this  tube  being  always  weighed  together.  In  the  second 
place,  traces  of  carbonic  acid  from  the  atmosphere  are  carried  into  the 
potash  apparatus  in  the  final  process  of  suction ; this  may  be  remedied 
by  connecting  the  tail  of  the  combustion  tube,  during  the  operation,  with 
a tube  containing  hydrate  of  potassa  by  means  of  a perforated  cork  or 
flexible  tube.  In  the  third  place,  it  happens  frequently,  in  the  analysis 
of  substances  containing  a considerable  proportion  of  water  or  of  hy- 
drogen, that  the  carbonic  acid  is  not  absolutely  dried  in  passing  through 
the  chloride  of  calcium  tube ; this  may  be  remedied  by  fixing  behind  the 
chloride  of  calcium  tube,  a tube  filled  with  asbestos  moistened  with  sul- 
phuric acid. 

Finally,  if  the  mixture  was  not  sufficiently  intimate,  traces  of  carbon 
remain  unconsumed.  It  is  therefore  better  to  complete  the  combustion 
in  oxygen  gas.  See  below. 

As  regards  the  hydrogen,  the  results  are  very  accurate,  if  the  filling 
is  skilfully  performed  with  dry  oxide  of  copper. 

§ 176. 

[ Completion  of  the  Combustion  by  Oxygen  Gas.  To  insure  the  oxi- 
dation of  the  last  traces  of  carbon  and  to  leave  the  oxide  of  copper  ready 
for  use  again,  it  is  advisable  to  finish  the  combustion  in  a stream  of 
oxygen.  For  this  purpose  the  tail  of  the  combustion  tube  must  be  made 
rather  stout  and  long.  When  the  potash-lye  recedes,  slip  tightly  over 
the  suitably  cooled  tail  a caoutchouc  tube  connected  with  a source  of 
pure  and  dry  oxygen  gas,  nip  off  the  tip  within  this  tube  by  help  of  a 
pliers,  and  cautiously  let  on  the  oxygen  until  the  reduced  copper  is  oxi- 
dized and  the  gas  traverses  the  potash-bulbs.  Then  replace  the  stream 
of  oxygen  by  one  of  pure  and  dry  air,  to  remove  all  oxygen  from  the 
bulbs.  To  prevent  loss  by  evaporation  from  the  potash-lye,  append  to 
the  potash-bulb  a small  tube  of  fragments  of  caustic  potash,  or  employ 
Mulder’s  absorption  apparatus,  fig.  90,  § 182. 

The  oxygen  may  be  supplied  from  a gasometer,  as  shown  fig.  84,  § 178, 
or  from  a small  tube-retort  of  fused  chlorate  of  potassa.  This  method 
and  that  of  § 175  are  not  applicable  to  organic  salts  of  the  alkalies  or 
alkali-earths,  since  these  bases  retain  a portion  of  carbonic  acid.] 

Combustion  with  Chromate  of  Lead,  or  with  Chromate  of  Lead 
and  Bichromate  of  Potassa.  • 

§ 177. 

This  method  is  especially  resorted  to  in  the  analysis  of  salts  of  or- 
ganic acids  with  alkalies  or  alkaline  earths  (as  the  chromic  acid  com- 
pletely displaces  carbonic  acid  from  their  bases),  and  of  bodies  contain- 
ing sulphur,  chlorine,  bromine,  or  iodine. 

Of  the  apparatus,  &c.,  enumerated  in  § 174,  all  are  required  except 
oxide  of  copper,  which  is  here  replaced  by  chromate  of  lead  (§  66,  2).  A 


432 


ORGANIC  ANALYSIS. 


narrow  combustion  tube  may  be  selected,  as  chromate  of  lead  contains 
a much  larger  amount  of  available  oxygen  in  an  equal  volume  than 
oxide  of  copper.  A quantity  of  the  chromate,  more  than  sufficient  to 
fill  the  combustion  tube,  is  heated  in  a platinum  or  porcelain  dish  over  a 
gas  or  Berzelius  lamp,  until  it  begins  to  turn  brown;  before  filling  it 
into  the  tube,  it  is  allowed  to  cool  down  to  100° ; and  even  below. 
The  process  is  conducted  as  the  one  described  in  § 174. 

One  of  the  principal  advantages  which  chromate  of  lead  has  over 
oxide  of  copper  as  an  oxidizing  agent  being  its  property  of  fusing  at  a 
high  heat,  the  temperature  must,  in  the  last  stage  of  the  process  of  com- 
bustion, be  raised  (by  fanning  the  charcoal,  &c.)  sufficiently  high  to  fuse 
the  contents  of  the  tube  completely,  as  far  as  the  substance  extends. 
To  heat  the  anterior  end  of  the  tube  to  the  same  degree  of  intensity 
would  be  injudicious,  since  the  chromate  of  lead  in  that  part  would 
thereby  lose  all  porosity,  and  thus  also  the  power  of  effecting  the  com- 
bustion of  the  products  of  decomposition  which  may  have  escaped  oxida- 
tion in  . the  other  parts  of  the  tube. 

As  the  chromate  of  lead,  even  in  powder,  is,  on  account  of  its  density, 
by  no  means  all  that  could  be  desired  in  this  latter  respect,  it  is  pre- 
ferable to  fill  the  anterior  part  of  the  tube,  instead  of  with  chromate  of 
lead,  with  coarsely  pulverized  strongly  ignited  oxide  of  copper,  or  with 
copper  turnings  which  have  been  superficially  oxidized  by  ignition  in  a 
muffle  or  in  a crucible  with  access  of  air. 

In  the  case  of  very  difficultly  combustible  substances — e.g .,  graphite 
— it  is  desirable  that  the  mass  should  not  only  readily  cake,  but  also,  in 
the  last  stage  of  the  process,  give  out  a little  more  oxygen  than  is  given 
out  by  chromate  of  lead.  It  is  therefore  advisable  in  such  cases  to  add  to 
the  latter  one-eighth  of  its  weight  of  fused  and  powdered  bichromate  of 
potassa.  With  the  aid  of  this  addition,  complete  oxidation  of  even  very 
difficultly  combustible  bodies  may  be  effected  (Liebig). 

3.  Combustion  with  Oxide  of  Copper  in  a Stream  of  Oxygen  Gas. 

§ 178. 

Many  chemists  effect  combustion  with  oxide  of  copper  in  a stream  of 
oxygen  supplied  by  a gasometer.  The  methods  based  upon  this  prin- 
ciple are  employed  not  only  for  the  analysis  of  difficultly  combustible 
bodies,  but  also  to  effect  the  determination  of  the  carbon  and  hydrogen 
in  organic  substances  in  general. 

These  methods  require  a gasometer  filled  with  oxygen,  and  another 
with  air,  together  with  certain  arrangements  to  dry  the  oxygen  and  air 
completely,  and  to  free  them  from  carbonic  acid.  They  are  resorted 
to  in  cases  where  a number  of  ultimate  analyses  have  to  be  made  in  suc- 
cession ; and  also  more  particularly  in  the  analysis  of  substances  which 
cannot  be  reduced  to  powder,  and  do  not  admit  therefore  of  intimate 
mixture  with  oxide  of  copper,  &c. 

The  heating  may  be  effected  with  the  charcoal  combustion  furnace 
(fig.  77,  p.  426),  but  a gas  furnace  is  most  convenient. 

Many  forms  of  gas-furjiace  have  been  employed.  One  of  the  best  is 
represented  in  fig.  84.  The  combustion  tube  rests  in  a gutter  of 
sheet  iron,  but  the  glass  is  kept  from  contact  with  the  metal  by  a layer 
of  asbestos.  It  is  well  to  secure  the  tube  to  the  gutter  by  binding 


ORGANIC  ANALYSIS. 


433 


§ 178.1 


wire.  At  its  anterior  end  the  combustion  tube  is  connected  with  a 
chloride  of  calcium  tube  and  potash-bulb  as  usual.  It  is  also  necessary 
to  have  a third  tube  to  collect  traces  of  moisture  which  the  current  of 
hot  gases  might  carry  over  from  the  potash  solution.  This  tube  i is 
filled  with  small  fragments  of  caustic  potash. 


Fig.  84. 


Posteriorly,  the  combustion  tube  is  joined  by  a cork  or  caoutchouc 
stopper  to  a narrow  glass  tube  which  connects  it  with  the  gasometer  and 
the  apparatus  for  drying  the  oxygen.  The  gas  on  leaving  the  gas- 
ometer streams  first  through  a potash  bulb-tube  <7,  then  through  a long 
U-tube,  e,  filled  with  chloride  of  calcium,  and  finally  through  the  U-tube 

containing  pumice  saturated  with  oil  of  vitriol.  It  is  well  to  attach  a 
lever  of  a foot  or  so  in  length  to  the  handle  of  the  cock  by  which  the 
supply  of  gas  is  admitted  to  the  combustion  tube,  as  thus  the  flosv  of  oxy- 
gen is  more  easily  regulated. 

a.  The  ignition  of  the  oxide  of  copper  is  effected  in  the  tube.  To 
accomplish  this,  a plug  of  asbestos  is  inserted  into  the  anterior  end, 
the  tube  being  then  filled  to  two-thirds  of  its  length  with  oxide  of  cop- 
per; the  posterior  orifice  is  then  joined  to  the  drying  apparatus  inter- 
posed between  the  gasometer  and  the  combustion  tube,  and  the  tube 
heated  to  gentle  redness  in  its  whole  length,  whilst  a slow  current  of 
atmospheric  air  is  conducted  through  it.*  After  complete  ignition  has 
been  effected  the  fire  is  extinguished,  the  anterior  end  of  the  combustion 
tube,  which  up  to  this  time  has  remained  open,  is  connected  with  an 
unweighed  chloride  of  calcium  tube,  and  the  ignited  oxide  allowed  to 
cool  in  a slow  stream  of  atmospheric  air.  When  the  tube  is  cold,  it  is 
opened  at  the  posterior  end,  the  substance  introduced  into  it  with  the 
aid  of  a long  tube  (compare  § 174),  andvquickly  mixed  wij,h  the  oxide 
by  means  of  a copper  wire  with  twisted  end  (see  fig.  76,  p.  174)  ; the 
after-part  of  the  tube  is  filled  to  within  12  cm.  with  ignited  oxide  of 
copper,  cooled  in  the  tube  or  flask  shown  in  fig.  75,  p.  174;  a few  gen- 
tle taps  on  the  table  will  suffice  to  shake  the  contents  down  a little, 
leaving  a clear  passage  above.  The  posterior  end  of  the  tube  is  then 
again  connected  with  /*,  and  the  chloride  of  calcium  tube,  affixed  to  the 


[Either  from  a second  gasometer,  or  by  aid  of  an  aspirator.  ] 
28 


434 


ORGANIC  ANALYSIS. 


[§  178. 


front  of  the  combustion  tube  during  the  cooling,  exchanged  for  the  one 
which  is  accurately  weighed,  and  to  which  the  weighed  tubes,  h,  and  i} 
are  also  joined. 

The  cock  of  the  oxygen  gasometer  is  now  opened  a little,  so  that  the 
gas  may  pass  in  a very  slow  current  through  the  apparatus  ; the  cock  is 
then  suddenly  turned  off,  and  the  level  of  the  fluid  in  the  two  bulb  tubes 
watched  some  time ; if  no  change  takes  place  in  it,  this  is  a proof  that 
all  the  joinings  are  air-tight.  After  this,  the  anterior  portion  of  the 
tube  is  heated  to  redness,  as  far  as  the  layer  of  pure  oxide  of  copper 
extends ; the  same  is  then  done  with  the  farther  part  also,  as  far  as  the 
layer  of  pure  oxide  of  copper  extends,  the  corks  at  both  ends  of  the 
tube  being  protected  by  screens,  as  well  as  also  the  part  containing  the 
mixture.  A very  slow  current  of  oxygen  gas  is  transmitted  all  the 
time  through  the  apparatus. 

The  part  of  the  tube  containing  the  mixture  is  then  also  heated,  pro- 
ceeding slowly  from  the  anterior  to  the  posterior  part.  The  stream  of 
oxygen  gas  is  gradually  increased,  but  never  to  an  extent  to  allow  the 
oxygen  to  escape  through  the  potash  bulbs  h.  When  the  tube  in  its 
whole  length  is  at  a red  heat,  and  the  evolution  of  gas  has  ceased,  the 
cock  is  opened  a little  wider,  and  the  transmission  of  oxygen  continued, 
until  at  last,  when  the  reduced  oxide  of  copper  is  completely  reoxi- 
dized, the  gas  begins  to  escape  unabsorbed  through  the  potash  bulbs. 
The  cock  of  the  oxygen  gasometer  is  now  shut,  whilst  that  of  the  air 
gasometer  is  opened  a little ; the  combustion  tube,  &c.,  are  allowed  to 
cool  in  a slow  stream  of  atmospheric  air.  The  chloride  of  calcium  tube, 
and  the  potash  bulbs  with  the  potassa  tube  joined  to  them,  are  then 
weighed. 

A very  great  advantage  of  this  method  consists  in  this,  that  the  com- 
bustion tube,  after  the  termination  of  the  first,  is  quite  ready  for  a 
second  analysis. 

b.  The  combustion  of  most  substances  may  be  effected  also  without 
mixing  with  oxide  of  copper,  by  introducing  the  sample  into  a platinum, 

copper,  or  porcelain  boat  or  tray  (fig. 
85).  This  method  affords  the  advan- 
tage of  enabling  the  operator  to  de- 
termine at  the  same  time  any  uncon- 
sumed residue  (ash)  that  may  remain 
behind,  which  in  some  cases — in  the 
analysis  of  coals,  for  instance — is  a great  convenience.  The  substance 
is  weighed  in  the  boat,  enclosed  in  a corked  glass  tube. 

The  process  of  combustion  is  then  conducted  as  follows  : — Introduce 
into  the  anterior  end  of  the  tube  a plug  of  asbestos,  then  fill  the  tube 
with  oxide  of  copper,  leaving  about  20  cm.  free,  and  keep  the  oxide  in 
its  place  by  pushing  an  asbestos  plug  down  upon  it.  Heat  the  tube 
now  to  redness  in  the  combustion  furnace,  pass  a current  of  air  through 
it,  to  remove  all  moisture,  connect  the  anterior  end  with  an  unweighed 
chloride  of  calcium  tube,  and  let  the  apparatus  cool ; then  push  the  boat 
containing  the  sample  down  to  the  rear  asbestos  plug,  and  connect  the 
after-part  of  the  tube  with  the  purifying  apparatus  interposed  between 
the  gasometer  and  the  combustion  tube,  the  fore-part  with  the  weighed 
chloride  of  calcium  tube  and  potash  bulbs  with  potassa  tube.  Heat  the 
oxide  of  copper  in  the  combustion  tube  to  redness,  and  when  approaching 
the  part  where  (the  boat  is  placed,  open  the  cock  of  the  oxygen  gasometer  a 


Fig.  85. 


179,  180.] 


ORGANIC  ANALYSIS. 


435 


little ; when  the  heat  has  reached  the  contents  of  the  boat,  proceed  with 
proper  caution,  and  take  care  to  pass  neither  too  little  nor  too  much 
oxygen  through  the  tube.  Increase  the  current  of  oxygen  a little  at  last, 
and  let  the  apparatus  finally  cool  in  a slow  current  of  atmospheric  air. 

With  this  method,  it  is  still  easier  than  with  a to  use  the  combustion 
tube  for  a second  analysis  immediately  after  the  first,  as  all  that  is 
required  for  the  purpose  is  to  insert  a fresh  boat  with  another  sample 
of  substance,  to  replace  the  one  just  removed. 


Volatile  Substances , or  Bodies  undergoing  Alteration  at  100° 
( losing  Water , for  instance). 

§ 179. 

The  process  is  conducted  either  according  to  § 174, 
or  as  directed  § 178.  Ignited  chromate  of  lead,  cooled 
in  a closed  tube,  may  also  be  employed  as  oxidizing 
agent. 

b.  Fluid  Bodies. 

a.  Volatile  liquids  (e.g.,  ethereal  oils,  alcohol,  &c.). 

§ 180. 

1.  The  analysis  of  organic  volatile  fluids  requires 
the  objects  enumerated  in  § 174.  The  combustion 
tube  should  be  somewhat  longer  than  there  men- 
tioned ; it  should  have  a length  of  50  or  60  cm.,  ac- 
cording as  the  substance  is  less  or  more  volatile.  The 
process  requires  besides  several  small  glass  bulbs  for 
the  reception  of  the  liquid  to  be  analyzed.  These 
bulbs  are  made  in  the  following  manner  : — 

A glass  tube,  about  30  cm.  long  and  about  8 mm. 
wide,  is  drawn  out  as  shown  in  fig.  86,  fused  off  at  d , 
and  A expanded  into  a bulb,  as  shown  in  fig.  87. 

The  bulbed  part  is  then  cut  off  at  /?.  Another  bulb  is 
then  made  in  the  same  way,  and  a third  and  fourth, 

. &c.,  as  long  as  sufficient  length  of  tube  is  left  to  se- 

tcure  the  bulb  from  being  reached  by  the  moisture  of 
the  mouth. 

_ Two  of  these  bulbs  are  accurately  weighed ; they  are 
' then  filled  with  the  liquid  to  be  analyzed,  closed  by  fu- 
sion, and  weighed  again.  The  filling  is  effected  by 
slightly  heating  the  bulb  over  a lamp  and  immersing  Fig.  87. 
the  point  into  the  liquid  to  be  analyzed,  part  of  which 
will  now,  upon  cooling,  enter  the  bulb.  If  the  fluid  is  highly 
volatile,  the  portion  entering  the  still  warm  bulb  is  converted 
c into  vapor,  which  expels  the  fluid  again;  but  the  moment  the 
vapor  is  recondensed,  the  bulb  fills  the  more  completely.  If 
the  liquid  is  of  a less  volatile  nature,  a small  portion  only  will 
enter  at  first;  in  such  cases  the  bulb  is  heated  again,  to  convert 
what  has  entered  into  vapor,  and  the  point  is  then  again  im- 
Fig.  86.  mersed  into  the  fluid,  which  will  now  readily  enter  and  fill  the 


436 


ORGANIC  ANALYSIS. 


[§  180 


bulb.  The  excess  of  fluid  is  ejected  from  the  neck  of  the  little 
tube  by  a sudden  jerk;  the  point  of  the  capillary  neck  is  then  sealed 
in  the  blowpipe  flame.  The  combustion  tube  is  now  prepared 
for  the  process  by  introducing  into  it  from  the  filling-tube  or  flask 
(§  174),  a layer  of  oxide  of  copper  occupying  about  6 cm.  in 
length.  The  middle  of  the  neck  of  one  of  the  bulbs  is  slightly  scratched 
with  a file,  the  pointed  end  is  quickly  broken  off,  and  the  bulb  and 
end  are  dropped  into  the  combustion  tube  (see  fig.  88).  Another 
layer  of  oxide  of  copper,  about  6 — 9 cm.  long,  is  then 
filled  in,  and  the  other  bulb  introduced  in  the  same  manner 
as  the  first.  The  tube  is  finally  nearly  filled  with  oxide  of 
copper.  A few  gentle  taps  upon  the  table  suffice  to  clear 
a free  passage  for  the  gases  evolved.  (It  is  advisable  to 
place  in  the  anterior  half  of  the  combustion  tube  small 
lumps  of  oxide  of  copper  [comp.  § 66,  1],  or  superficially 
oxidized  copper  turnings,  which  will  permit  the  free  pas- 
sage of  the  gases,  even  with  a narrow  channel,  or  no 
channel  at  all ; since  with  a wide  channel  there  is  the  risk 
of  vapors  passing  unconsumed  through  the  tube.) 

The  combustion  of  highly  volatile  substances  demands 
great  care,  and  requires  certain  modifications  of  the  com- 
mon method.  The  operation  commences  by  heating  to 
redness  the  anterior  half  of  the  tube,  which  is  separated 
from  the  rest  by  a screen,  or  in  the  case  of  highly  volatile 
substances,  by  two  screens  ; ignited  charcoal  is  then  placed 
behind  the  tube  to  heat  the  tail  and  prevent  the  conden- 
sation of  vapor  in  that  part.  A piece  of  red-hot  charcoal 
is  now  applied  to  that  part  of  the  tube  which  is  occupied 
Fig.  88.  by  the  first  bulb  ; this  causes  the  efflux  and  evaporation 
of  the  contents  of  the  latter  ; the  vapor  passing  over  the 
oxide  of  copper  suffers  combustion,  and  thus  the  evolution  of  gas  com- 
mences, which  is  then  maintained  by  heating  very  gradually  the  first, 
and  after  this  the  second  bulb ; it  is  better  to  conduct  the  operation  too 
slowly  than  too  quickly.  Sudden  heating  of  the  bulbs  would  at  once 
cause  such  an  impetuous  rush  of  gas  as  to  eject  the  fluid  from  the 
potash  bulbs.  The  tube  is  finally  in  its  entire  length  surrounded  with 
ignited  charcoal,  and  the  rest  of  the  operation  conducted  in  the  usual 
way.  If  the  air  drawn  through  the  apparatus  tastes  of  the  analyzed 
substance,  this  is  a sure  sign  that  complete  combustion  has  not  been 
effected. 

2.  In  the  combustion  of  liquids  of  high  boiling  point  and  abound- 
ing in  carbon,  e.g.y  ethereal  oils,  unconsumed  carbon  is  apt  to  deposit 
on  the  completely  reduced  copper  near  the  substance ; it  is  therefore 
advisable  to  distribute  the  quantity  intended  for  analysis  (about  0'4 
grin.)  in  3 bulbs,  separated  from  each  other  in  the  tube  by  layers  of 
oxide  of  copper. 

3.  In  the  combustion  of  less  volatile  liquids,  it  is  advisable  to  empty 
the  bulbs  of  their  contents  before  the  combustion  begins  : this  is  effected 
by  connecting  the  filled  tube  with  an  exhausting  syringe,  and  rarefying 
the  air  in  the  tube  by  a single  pull  of  the  handle;  this  will  suffice  to 
expand  the  air-bubble  in  each  bulb  sufficiently  to  eject  the  oily  liquid 
from  it,  which  is  then  absorbed  by  the  oxide  of  copper. 

4.  If  there  is  reason  to  apprehend  that  the  oxide  of  copper  may  not 


181.] 


ORGANIC  ANALYSIS. 


437 


suffice  to  effect  the  complete  combustion  of  the  carbon,  the  process  is 
terminated  in  a stream  of  oxygen  gas  (compare  § 176). 

5.  If  it  is  intended  to  effect  the  combustion  in  the  apparatus  de- 
scribed in  § 178  (in  a current  of  oxygen  gas),  the  bulb  must  be  drawn  out 
to  a fine  long  point,  and  filled  almost  completely  with  the  fluid.  The 
point  is  then  sealed  in  the  blowpipe  flame,  and  the  bulbs  are  transferred 
in  that  state  to  the  combustion  tube.  When  the  anterior  and  the  far- 
ther end  of  the  tube  are  red-hot,  a piece  of  ignited  charcoal  is  put  to 
the  part  occupied  by  the  first  bulb,'  when  the  expansion  of  the  liquid 
will  cause  it  to  burst.  When  the  contents  of  the  first  bulb  are  con- 
sumed, the  second,  and  after  this  the  third,  are  treated  in  the  same  way. 
This  method  will  not  answer,  however,  for  very  volatile  liquids,  as,  e.g., 
ether,  on  account  of  the  explosion  which  would  inevitably  take  place. 

3.  Non-volatile  Liquids  (e.g.,  fatty  oils). 

8 181. 


Fig.  89. 


The  combustion  of  non-volatile  liquids  is  effected  either,  1,  with  chro- 
mate of  lead,  or  oxide  of  copper  and  oxygen;  2,  in  the  apparatus  de- 
scribed § 178. 

1.  The  operation  is  conducted  in  general  as  directed  §175  or  §176. 
The  substance  is  weighed  in  a small  tube,  placed  for  that  purpose  in  a 
tin  foot  (see  fig.  89),  and  the  mixing  effected  as  follows: — 

Introduce  into  the  combustion  tube  first  a layer,  about  6 cm. 
long,  of  chromate  of  lead,  or  of  oxide  of  copper;  then  drop 
in  the  small  cylinder  with  the  substance,  and  let  the  oil  com- 
pletely run  out  into  the  tube ; make  it  spread  about  in 
various  directions,  taking  care,  however,  to  leave  the  upper 
side  (intended  for  the  channel)  and  the  forepart,  to  the  ex- 
tent of  or  of  the  length  of  the  tube,  entirely  clean.  Fill 
the  tube  now  nearly  with  chromate  of  lead  or  oxide  of  cop- 
per,— which  has  previously  been  cooled  in  the  filling  tube  or 
flask, — taking  care  that  the  little  cylinder  which  contained  the  oil  be 
completely  filled  with  the  oxidizing  agent.  Place  the  tube  in  hot  sand, 
which,  imparting  a high  degree  of  fluidity  to  the  oil,  leads  to  the  per- 
fect absorption  of  the  latter  by  the  oxidizing  agent,  and  proceed  with 
the  combustion  in  the  usual  way.  It  is  advisable  to  select  a tolerably 
long  tube.  Chromate  of  lead  is  usually  to  be  preferred.  If  it  is  used, 
a very  intense  heat,  sufficiently  strong  to  fuse  the  contents  of  the  tube, 
is  cautiously  applied  in  the  last  stage  of  the  process. 

Solid  fats  or  waxy  substances  which,  not  being  reducible  to  powder, 
cannot  be  mixed  with  the  oxidizing  agent  in  the  usual  way,  are  treated 
in  a similar  manner  to  fatty  oils.  They  are  fused  in  a small  weighed 
glass  boat,  made  of  a tube  divided  lengthwise  ; when  cold,  the  little  boat 
with  its  contents  is  weighed,  and  then  dropped  into  the  combustion  tube, 
which  has  been  previously  filled  to  the  extent  of  about  6 cm.  with 
chromate  of  lead,  or  with  oxide  of  copper.  The  substance  is  then 
fused  by  the  application  of  heat,  and  made  to  spread  about  in  the  tube 
in  the  same  manner  as  is  done  with  fatty  oils ; the  rest  of  the  operation 
also  being  conducted  exactly  as  in  the  latter  case.  If  chromate  of  lead 
is  employed,  it  will  be  found  advantageous  to  add  some  bichromate  of 


ORGANIC  ANALYSIS. 


438 


L§  182. 


potassa  (§177).  If  oxide  of  copper  be  used,  finish  in  a stream  of 
oxygen  (§  176). 

2.  If  it  is  intended  to  effect  the  combustion  of  fatty  substances  or 
other  bodies  of  the  kind  in  a current  of  oxygen  gas,  in  the  apparatus 
described  in  § 178,  the  substance  is  weighed  in  a porcelain  or  platinum 
boat,  which  is  then  inserted  into  the  tube,  and  the  posterior  part  of  the 
latter  filled  with  oxide  of  copper,  as  directed  above.  The  combustion 
must  be  conducted  with  great  care.  As  soon  as  the  oxide  of  copper  in 
the  anterior  and  the  posterior  parts  of  the  tube  is  red-hot,  a piece  of 
red-hot  charcoal  is  put  to  the  part  occupied  by  the  little  boat.  The 
volatile  products  generated  by  the  dry  distillation  of  the  substance  bum 
at  the  expense  of  the  oxide  of  copper. 

When  it  is  perceived  that  the  surface  layer  of  the  oxide  of  copper  is 
reduced,  the  application  of  heat  to  the  substance  is  suspended  for  a 
time,  and  resumed  only  after  the  reduced  copper  is  reoxidized  in  the 
stream  of  oxygen  gas.  Care  is  finally  taken  to  insure  the  complete 
combustion  of  the  carbon  remaining  in  the  boat. 


Supplement  to  A.,  §§  174 — 181. 

§182. 

Modified  Apparatus  for  the  Absorption  of  Carbonic  Acid. 

G.  J.  Mulder  * has  replaced  the  potash  bulbs  altogether  by  a totally 
different  absorption  apparatus,  viz.,  by  the  apparatus  already  described, 
p.  293.  The  chloride  of  calcium  tube  is  immediately  connected  with 
the  system  of  TJ-tubes,  fig.  90  ; a contains  small  pieces  of  glass,  6 to  10 
drops  concentrated  sulphuric  acid,  and  at  the  top  asbestos  plugs,  b is 
filled  to  | with  granulated  soda-lime  (say  20  grm.),  the  remaining  (in 
the  2d  limb)  contains  chloride  of  calcium  (say  3 grm.).  Lastly,  c is 
filled  with  lumps  of  hydrate  of  potassa.  a and  b are  weighed  together, 

c serves  as  a guard  to  b , and  is  not 
weighed.  The  sulphuric  acid  tube 
serves  to  show  the  rate  of  the  evolu- 
tion of  gas  ; it  contains  enough  sul- 
phuric acid,  when  the  lower  part  is 
just  stopped  up.  If  the  process 
goes  on  properly,  the  weight  of  the 
tube  does  not  increase  more  than  1 
mgrm.  ; generally  the  increment  is 
unweighable.  If  the  tube  is  closed 
after  use  with  caoutchouc  caps,  it 
may  be  used  over  and  over  again. 
The  sulphuric  acid  possesses  the  ad- 
vantage over  other  fluids  that  it  in- 
dicates whether  the  combustion  was 
complete  or  not;  for  in  the  first 
case  it  remains  colorless,  in  the  sec- 
ond it  becomes  brown  from  the  escaping  hydrocarbons,  and  then  the 
results  cannot  be  expected  to  be  perfectly  accurate.  The  absorption  of 
the  carbonic  acid  by  the  soda-lime  tube  is  as  rapid  as  it  is  complete; 


* Zeitschrift  f.  analyt.  Chem.  1,  2. 


§ 183.1 


ORGANIC  ANALYSIS. 


439 


even  when  a stream  of  carbonic  acid  is  passing,  with  ten  times  the  ra- 
pidity usual  in  organic  analysis,  no  trace  of  the  acid  makes  its  escape. 
The  absorption  of  the  carbonic  acid  is  attended  with  warming  of  the  soda- 
lime  ; if  any  water  evaporates  from  the  soda-lime,  it  is  retained  by  the 
chloride  of  calcium  in  the  second  limb.  The  corks  of  the  absorption 
tubes  are,  like  the  others,  coated  with  sealing-wax.  A filled  soda-lime 
tube  weighs  about  40  grm.  The  first  time  it  is  used  alone  ; the  second 
time  the  same  tube  is  used,  but  as  a precautionary  measure  a second 
similarly  filled  and  separately  weighed  tube  is  placed  in  front  of  it. 
The  second  tube  rarely  increases  in  weight,  and  unless  it  does,  the 
first  tube  can  be  used  a third  time,  but  of  course  in  connection  with  the 
second.  If  the  second  tube  has  gained  in  the  third  operation,  the  first 
tube  is  rejected  at  the  fourth  operation,  and  the  second  is  now  used 
alone,  &c.  If  after  the  combustion  a stream  of  oxygen  is  transmitted 
through  the  combustion  tube,  the  tubes  are  of  course  at  the  end  full  of 
oxygen.  If,  then,  care  be  taken  that  the  tubes  are  full  of  oxygen  before 
weighing,  the  trouble  of  the  final  transmission  of  air  may  be  saved. 
For  weighing,  Mulder  closes  the  ends  of  the  glass  tubes  with  caps 
made  out  of  india-rubber  tube. 

Mulder’s  absorption  apparatus  is  peculiarly  suitable,  when  the  car- 
bonic acid  is  mixed  with  another  gas.  It  insures  complete  absorption, 
precludes  the  evaporation  of  any  water,  and  offers  perfect  security  in 
case  of  the  sudden  occurrence  of  a too  rapid  evolution  of  gas. 

B.  Analysis  of  Compounds  consisting  of  Carbon,  Hydrogen, 
Oxygen,  and  Nitrogen. 

The  principle  of  the  analysis  of  such  compounds  is  in  general  this : 
in  one  portion  the  carbon  and  the  hydrogen  are  determined  as  carbonic 
acid  and  water  respectively;  in  another  portion , the  nitrogen  is  deter- 
mined either  in  the  gaseous  form,  or  as  chloride  of  ammonium  and  bi- 
chloride of  platinum,  or  by  neutralizing  the  ammonia  formed  from  the 
nitrogen ; the  oxygen  is  calculated  from  the  loss. 

As  the  presence  of  nitrogen  exercises  a certain  influence  upon  the 
estimation  of  carbon  and  hydrogen,  we  have  here  to  consider  not  only 
the  method  of  determining  the  nitrogen,  but  also  the  modifications 
which  the  presence  of  the  nitrogen  renders  necessary  in  the  usual  me- 
thod of  determining  the  carbon  and  hydrogen. 

a . Determination  of  the  Carbon  and  Hydrogen  in  Nitrogenous 

Substances. 

§ 183. 

1.  When  nitrogenous  substances  are  ignited  with  oxide  of  copper  or 
with  chromate  of  lead,  a portion  of  the  nitrogen  present  escapes  in  the 
gaseous  form,  together  with  the  carbonic  acid  and  aqueous  vapor ; 
whilst  another  portion,  minute  indeed,  still,  in  bodies  abounding  in 
oxygen,  not  quite  insignificant,  is  converted  into  nitric  oxide  gas,  which 
is  subsequently  transformed  wholly  or  partially  into  nitrous  acid  by  the 
air  in  the  apparatus.  The  application  of  the  methods  described  in  §§ 
174,  &c.,  in  the  analysis  of  nitrogenous  substances  would  accordingly 
give  too  much  carbon ; since  the  potash  bulbs  would  retain,  besides  the 
carbonic  acid,  also  the  nitrous  acid  formed  and  a portion  of  the  nitric 


440 


ORGANIC  ANALYSIS. 


oxide  (which  in  the  presence  of  potassa  decomposes  slowly  into  nitrous 
acid  and  nitrous  oxide.)  This  defect  may  be  remedied  by  selecting  a 
combustion  tube  about  12 — 15  cm.  longer  than  those  commonly  em- 
ployed, filling  this  in  the  usual  way,  but  finishing  with  a loose  layer, 
about  9 — 12  cm.  long,  of  clean,  fine  copper  turnings  (§  66,  5),  or  a 
compact  roll  of  copper  wire-gauze.*  The  process  is  commenced  by 
heating  these  copper  turnings  to  redness,  in  which  state  they  are  main- 
tained during  the  whole  course  of  the  operation.  These  are  the  only 
modifications  required  to  adapt  the  methods  above  described,  for  the 
analysis  of  nitrogenous  substances.  The  use  of  the  metallic  copper 
depends  upon  its  property  of  decomposing,  when  in  a state  of  intense 
ignition,  all  the  oxides  of  nitrogen  into  oxygen,  with  which  it  combines, 
and  into  pure  nitrogen  gas.  As  the  metal  exercises  this  action  only 
when  in  a state  of  intense  ignition,  care  must  be  taken  to  maintain  the 
anterior  part  of  the  tube  in  that  state  throughout  the  process.  As  me- 
tallic copper  recently  reduced  retains  hydrogen  gas,  and,  when  kept  for 
some  time,  aqueous  vapor  condensed  on  the  surface,  the  copper  turnings 
intended  for  the  process  must  be  introduced  into  the  tube  hot  as  they 
come  from  the  drying  closet  (which  is  heated  to  100°).  v.  Lie- 
big recommends  to  compress  the  hot  turnings  in  a tube  into  a cylinv 
drical  form,  to  facilitate  their  rapid  introduction  into  the  combus- 
tion tube. 

2.  If  it  is  intended  to  burn  nitrogenous  bodies  in  the  apparatus 
described  in  § 178,  the  combustion  tube  should  be  about  80  cm.  long, 
and  the  anterior  part  of  it  filled  with  a layer  15—18  cm.  long,  of  clean 
copper  turnings.  Care  must  be  taken  to  keep  at  least  the  anterior  half 
of  the  turnings  from  oxidizing,  both  during  the  ignition  in  the  current 
of  air  and  during  the  actual  process  of  combustion.  When  the  opera- 
tion is  terminated,  and  the  oxidation  of  the  metallic  copper  is  visibly 
progressing,  the  oxygen  is  turned  off,  and  the  cock  of  the  air  gasometer 
opened  a little  instead,  to  let  the  tube  cool  in  a slow  stream  of  atmos- 
pheric air. 

b.  Determination  of  the  Nitrogen  in  Organic  Compounds. 

As  already  indicated,  two  essentially  different  methods  are  in  use  for 
effecting  the  determination  of  the  nitrogen  in  organic  compounds ; 
viz.,  the  nitrogen  is  either  separated  in  the  pure  form  and  its  volume 
measured,  or  it  is  converted  into  ammonia,  and  this  is  determined 
either  as  bichloride  of  platinum  and  chloride  of  ammonium,  or  by  neu- 
tralization. 

a.  Determination  of  the  Nitrogen  from  the  Volume. 

§ 184- 

Dumas’  Method,  modified  by  Schiel. 

This  method  may  be  employed  in  the  analysis  of  all  organic  compounds 
containing  nitrogen.  It  requires  a graduated  glass  cylinder  of  about 
200  c.  c.  capacity,  with  a ground-glass  plate  to  cover  it. 

* The  copper  turnings  cannot  be  replaced  by  the  metallic  powder  obtained  by  the 
reduction  of  the  oxide  with  hydrogen,  as  this  obstinately  retains  hydrogen,  and 
consequently  decomposes  appreciable  quantities  of  carbonic  acid  with  formation 
of  carbonic  oxide.  Schr  hter,  Lautemann,  Journ.  f.  prakt.  Chem.  77,  316. 


§ 184.1 


ORGANIC  ANALYSIS. 


441 


The  combustion  tube  should  be  60  or  70  cm.  long,  and  drawn  out  at 
the  posterior  end  to  a stout  open  tail,  which  should  have  a small  bulb  or 
swell  for  the  better  fastening  of  a rubber  tube  to  it.  Introduce  into  it 
near  the  tail  a plug  of  newly  ignited  asbestos,  then  a layer  of  oxide  of 
cojjper,  4 cm.  long ; after  this  the  intimate  mixture  of  an  accurately 
weighed  portion  of  the  substance  (0*3 — 06  grm.,  or,  in  the  case  of  com- 
pounds poor  in  nitrogen,  a somewhat  larger  quantity)  with  oxide  of  cop 
per,  then  the  oxide  which  has  served  to  rinse  the  mortar,  followed  by 
a layer  of  pure  oxide,  and  lastly,  a layer  of  copper  turnings,  about  15 
cm.  long.  Make  a channel  along  the  top  of  the  tube  by  gentle  tapping. 
Connect  the  tube  with  the  bent  delivery  tube  c f (fig.  91),  and  place 


in  the  furnace.  Connect  the  tail  by  means  of  a stout  tube  of  india  rub- 
ber with  an  apparatus  for  giving  a continuous  stream  of  washed  car- 
bonic acid  gas.  Transmit  this  slowly  through  the  tube  for  half  an  hour, 
then  immerse  the  end  of  the  bent  delivery  tube  under  mercury,  and 
invert  over  it  a test  tube  filled  with  solution  of  potassa.  If  the  gas 
bubbles  entering  the  cylinder  are  completely  absorbed  by  the  solution 
of  potassa,  this  is  a proof  that  the  air  is  thoroughly  expelled  from  the 
tube.  But  should  this  not  be  the  case,  the  evolution  of  carbonic  acid 
must  be  continued  until  the  desired  point  is  attained.  When  the  gas  is 
completely  absorbed,  close  the  communication  between  the  C02  genera- 
tor and  the  combustion  tube  by  a screw  clamp  or  stop-cock,  invert  the 
graduated  cylinder,  filled  §-  with  mercury,  ^ with  concentrated  solution 
of  potassa,  over  the  end  of  the  delivery  tube,  with  the  aid  of  a ground- 
glass  plate,*  and  proceed  with  the  combustion  in  the  usual  way,  heating 
first  the  anterior  end  of  the  tube  to  redness,  and  advancing  gradually 
towards  the  farther  end.  In  the  last  stage  of  the  process,  communica 
tion  is  reestablished  with  the  C02  generator,  and  thus  the  whole  of  the 
nitrogen  gas  which  still  remains  in  the  tube  is  forced  into  the  cylinder. 
Wait  now  until  the  volume  of  the  gas  in  the  cylinder  no  longer  decreases, 
even  upon  shaking  the  latter  (consequently,  until  the  whole  of  the  car- 
bonic acid  has  been  absorbed),  then  place  the  cylinder  in  a large  and 
deep  glass  vessel  filled  with  water,  the  transport  from  the  mercurial 
trough  to  this  vessel  being  effected  by  keeping  the  aperture  closed  with 

* The  following  is  the  best  way  of  filling  the  cylinder  and  inverting  it  over 
the  opening  of  the  bent  delivery  tube : — The  mercury  is  introduced  first,  and 
the  air-bubbles  which  adhere  to  the  walls  of  the  vessel  are  removed  in  the  usual 
way.  The  solution  of  potassa  is  then  poured  in,  leaving  the  top  of  the  cylinder 
free,  to  the  extent  of  about  2 lines ; this  is  cautiously  filled  up  to  the  brim  with 
pure  water,  and  the  ground-glass  plate  slided  over  it.  The  cylinder  is  now  in- 
verted, and  the  opening  placed  under  the  mercury  in  the  trough ; the  glass  plate, 
is  then  withdrawn  from  under  the  cylinder.  In  this  manner  the  operation  may 
be  performed  easily,  and  without  soiling  the  fingers. 


442 


ORGANIC  ANALYSIS. 


L§  185. 


a small  dish  filled  with  mercury.  The  mercury  and  the  solution  of 
■potassa  sink  to  the  bottom,  and  are  replaced  by  water.  Immerse  the 
cylinder,  then  raise  it  again  until  the  water  is  inside  and  outside  on  an 
exact  level ; read  off  the  volume  of  the  gas  and  mark  the  temperature 
of  the  water  and  the  state  of  the  barometer  ; calculate  the  weight  of  the 
nitrogen  gas  from  its  volume,  after  reduction  to  the  normal  tempera- 
ture and  pressure,  and  with  due  regard  to  the  tension  of  the  aqueous 
vapor  (comp.  (i  Calculation  of  Analyses”).  The  results  are  generally 
somewhat  too  high,  viz.,  by  about  0*2 — 0*5  per  cent. ; this  is  owing  to 
the  circumstance  that  even  long-continued  transmission  of  carbonic  acid 
through  the  tube  fails  to  expel  every  trace  of  atmospheric  air  adhering 
to  the  oxide  of  copper. 

It  is  highly  advisable,  before  making  any  nitrogen  determinations 
with  this  method,  to  subject  a non-nitrogenous  substance,  e.g .,  sugar, 
to  the  same  process.  The  analyst  thereby  acquaints  himself  with  the 
extent  of  the  error  to  which  he  will  be  exposed.  In  such  an  experi- 
ment the  quantity  of  unabsorbed  gas  should  not  exceed  1 or  1^  c.c. 

To  insure  complete  combustion  of  difficultly  combustible  bodies, 
Strecker  recommends  the  addition  of  arsenious  acid  in  powder  to  the 
oxide  of  copper  with  which  the  substance  is  to  be  mixed  ; the  arsenious 
acid  is  volatilized  by  the  action  of  the  heat,  the  fumes  burning  the  whole 
of  the  carbon  like  a current  of  oxygen.  The  arsenious  acid  sublimes  in 
the  anterior  part  of  the  tube,  arsenic  remains  in  the  copper. 

[Frankland  * and  Gibbs  f employ  the  Sprengel  mercury  pump  to  ex- 
haust the  combustion  tube  of  air  previous  to  the  combustion,  and  after- 
wards to  transfer  the  nitrogen  to  the  receiver,  and  obtain  very  accurate 
results.]  » 

/?.  Determination  of  Nitrogen  by  conversion  into  Ammonia. 

Varrentrapp  and  Will’s  Method. 

§185. 

This  method  may  be  applied  to  all  nitrogenous  compounds,  except 
(those  containing  the  nitrogen  in  the  form  of  nitric  acid,  hyponitric  acid, 
&c.J  It  is  based  upon  the  same  principle  as  the  method  of  examining 
organic  bodies  for  nitrogen  (§  172,  1,  a),  viz.,  upon  the  circumstance  that, 
.when  nitrogenous  bodies  are  ignited  with  the  hydrate  of  an  alkali,  the 
water  of  hydration  of  the  latter  is  decomposed,  the  oxygen  forming  with 
the  carbon  of  the  organic  body  carbonic  acid,  which  then  combines  with 
the  alkali,  whilst  the  Rydrogen  at  the  moment  of  its  liberation  combines 
with  the  whole  of  the  nitrogen  present  to  ammonia. 

! In  the  case  of  substances  abounding  in  nitrogen,  such  as  uric  acid, 
mellon,  &c.,  the  whole  of  the  nitrogen  is  not  at  once  converted  into 
ammonia  in  this  process ; a portion  of  it  combining  with  part  of  the 
carbon  of  the  organic  matter  to  cyanogen,  which  then  combines,  either 
in  that  form  with  the  alkali  metal,  or  in  form  of  cyanic  acid  with  the 
alkali.  Direct  experiments  have  proved,  however,  that  even  in  such 
cases  the  whole  of  the  nitrogen  is  ultimately  obtained  as  ammonia,  if 

[*  Journal  Chem.  Soc.,  1868,  p.  90.] 

[f  Unpublished  paper  read  before  National  Academy  of  Sciences,  Aug.,  1868.] 
Vegetable  matters,  as  dried  plants,  containing  not  more  than  3 per  cent,  of 
NO  5 may  be  analyzed  by  this  method.  In  a case  where  6 per  cent,  of  N05  was  pre- 
sent, a loss  of  0’2  per  cent,  of  N took  place  in  the  experiments  of  E.  Schulze. — 
Fres.  Zeitschrift  vi.,  387]. 


185.] 


ORGANIC  ANALYSIS. 


443 


tlie  hydrated  alkali  is  present  in  excess,  and  the  heat  applied  sufficiently 
intense. 

As  in  all  organic  nitrogenous  compounds  the  carbon  preponderates  over 
the  nitrogen,  the  oxidation  of  the  former,  at  the  expense  of  the  water, 
will  invariably  liberate  a quantity  of  hydrogen  more  than  sufficient  tc 
convert  the  whole  of  the  nitrogen  present  into  ammonia  ; for  instance, 
C2N+4  H 0=2  C Oa+N  H3+H. 

The  excess  of  the  liberated  hydrogen  escapes  either  in  the  freo  state, 
or  in  combination  with  the  not  yet  oxidized  carbon,  according  to  the 
relative  proportions  of  the  two  elements  and  the  temperature,  as  marsh 
gas,  olefiant  gas,  or  vapor  of  readily  condensible  hydrocarbons,  which 
gases  serve  in  a certain  measure  to  dilute  the  ammonia.  As  a certain 
dilution  of  that  product  is  necessary  for  the  success  of  the  operation,  I 
will  here  at  once  state  that  substances  rich  in  nitrogen  should  be  mixed 
with  more  or  less  of  some  non-nitrogenous  body — sugar,  for  instance — 
so  that  there  may  be  no  deficiency  of  diluent  gas. 

The  ammonia  is  determined  volumetrically,  see  § 208. 
aa.  Requisites. 

1.  The  objects  enumerated  § 174,  and  a Porcelain  Mortar  for  weigh- 
ing and  mixing  the  substance. 

2.  A Combustion-tube  of  the  kind  described  § 174,  3 ; length  about 
40  cm.,  width  about  12  mm.  The  combustion  is  effected  in  an  ordi- 
nary combustion  furnace  (§  174,  11). 

3.  Soda-Lime. — (§  66,  4).  It  is  advisable  to  gently  heat  in  a pla- 
tinum or  porcelain  dish,  a quantity  of  the  soda-lime  sufficient  to  fill  the 
combustion  tube,  so  as  to  have  it  perfectly  dry  for  the  process  of  com- 
bustion. In  the  analysis  of  non-volatile  substances,  the  best  way  is  to 
use  the  soda-lime  while  still  warm. 

4.  Asbestos. — A small  portion  of  this  substance  is  ignited  in  a pla- 
tinum crucible  previous  to  use. 

5.  A Yarrentrapp  and  Will’s  Bulb-apparatus. — This  may  be  ob- 
tained from  the  shops.  Pig.  92  shows  its  form.  It  is  filled  to  the 


Fig.  92. 


extent  indicated  in  the  drawing  with  standard  sulphuric  acid  § 204,  of 
which  20  c.c.  should  be  employed.  The  acid  is  introduced  either  by 
dipping  the  point  into  the  acid,  and  applying  suction  to  J,  or  by  means 
of  a burette. 

In  order  to  guard  against  the  receding  of  the 
acid  into  the  combustion  tube,  Arendt  and  Knop 
have  suggested  the  form  indicated  fig.  93. 

6.  A soft,  well-perforated  Cork,  which  fits  the 
combustion  tube  air-tight,  and  in  which  the  tube  d 
of  the  bulb  apparatus  fits  closely. 

7.  A Suction-tube  of  caoutchouc  adapted  to  the 
point  of  the  bulb  apparatus. 


Fig.  93. 


444 


ORGANIC  ANALYSIS. 


[§  185. 


bb.  The  Process. 

The  combustion  tube  is  half  filled  with  soda-lime,  which  is  then  gra- 
dually transferred  to  the  perfectly  dry,  and,  if  the  nature  of  the  sub- 
stance permits,  rather  warm  mortar,  where  it  is  most  intimately  mixed 
with  the  weighed  substance,  forcible  pressure  being  carefully  avoided ; 
a layer  of  soda-lime,  occupying  about  3 cm.,  is  now  introduced  into 
the  posterior  part  of  the  combustion  tube,  and  the  mixture  filled-in 
after;  the  latter,  which  will  occupy  about  20  cm.,  is  followed  bv  a 
layer  of  about  5 cm.  of  soda-lime,  which  has  been  used  to  rinse  the 
mortar,  and  this  again  by  a layer  of  12  cm.  of  pure  soda-lime,  leaving 
thus  about  4 cm.  of  the  tube  clear.  The  tube  is  then  closed  with 
a loose  plug  of  asbestos,  and  a free  passage  for  the  evolved  gases 
formed  by  a few  gentle  taps  ; it  is  then  connected  with  the  bulb  ap- 
paratus by  means  of  the  perforated  cork,  and  finally  placed  in  the  com- 
bustion furnace  (see  fig.  92). 

To  ascertain  whether  the  apparatus  closes  air-tight,  some  air  is  ex- 
pelled by  holding  a piece  of  red-hot  charcoal  to  the  bulb  a,  and  the  ap- 
paratus observed,  to  see  whether  the  liquid  will,  upon  cooling,  perma- 
nently assume  a higher  position  in  a than  in  the  other  limb.  The  tube 
is  then  gradually  surrounded  with  ignited  charcoal,  commencing  at  the 
anterior  part,  and  progressing  slowly  towards  the  tail,  the  operation 
being  conducted  exactly  as  in  an  ordinary  combustion  (§  175).  Care 
must  be  taken  to  keep  the  anterior  part  of  the  tube  tolerably  hot 
throughout  the  process,  since  this  will  almost  entirely  prevent  the 
passage  of  liquid  hydrocarbons,  the  presence  of  which  in  the  standard 
acid  would  be  inconvenient.  The  asbestos  should  be  kept  sufficiently 
hot  to  guard  against  its  retaining  water,  and  with  this,  ammonia.  The 
combustion  should  be  conducted  so  as  to  maintain  a steady  and  unin- 
terruped  evolution  of  gas ; there  is  no  fear  of  any  ammonia  escaping 
unabsorbed,  even  if  the  evolution  is  rather  brisk ; but  the  operator  must 
constantly  be  on  his  guard  against  the  receding  of  the  acid,  which  takes 
place  the  moment  the  evolution  of  gas  ceases,  and  this,  in  some  in- 
stances, with  such  impetuosity  as  to  force  the  acid  into  the  combustion 
tube,  which  of  course  spoils  the  whole  analysis.  This  difficulty  may  be 
readily  met,  however,  by  mixing  with  the  substance  an  equal  quantity 
of  sugar,  which  will  give  rise  to  the  evolution  of  more  permanent  gases 
diluting  the  ammonia. 

When  the  tube  is  ignited  in  its  whole  length,  and  the  evolution  of 
gas  has  totally  ceased,*  the  point  of  the  combustion  tube  is  broken  off, 
and  air  to  the  extent  of  several  times  the  volume  of  the  gas  in  the  tube 
is  sucked  through  the  apparatus,  to  force  all  the  rest  of  the  ammonia 
into  the  acid. 

Liquid  nitrogenous  compounds  are  weighed  in  small  sealed  glass  bulbs, 
and  the  process  is  conducted  as  directed  § 180,  with  this  difference,  that 
soda-lime  is  substituted  for  oxide  of  copper.  It  is  advisable  to  employ 
tubes  of  greater  length  for  the  combustion  of  liquids  than  are  required 
for  solid  bodies.  The  best  method  of  conducting  the  operation,  is  to 
heat  first  about  one-third  of  the  tube  at  the  anterior  end,  and  then  to 
force  the  liquid  from  the  bulbs  into  the  tube  by  heating  the  hinder 
end  of  the  latter;  the  expelled  liquid  will  thus  become  diffused  in  the 


* This  is  indicated  by  the  white  color  which  the  mixture  reassumes  when  all 
the  carbon  deposited  on  the  surface  is  oxidized. 


§ 186.] 


ORGANIC  ANALYSIS. 


445 


central  part  of  the  tube,  without  being  decomposed.  By  a progressive 
application  of  heat,  proceeding  slowly  from  the  anterior  to  the  posterior 
end,  a steady  and  uniform  evolution  of  gas  may  be  easily  maintained. 

When  the  combustion  is  terminated,  the  bulb  apparatus  is  emptied, 
through  the  opening  at  the  point  into  a beaker,  and  rinsed  with  water 
until  the  rinsings  cease  to  manifest  acid  reaction. 

The  excess  of  acid  is  determined  by  means  of  standard  potash  solu- 
tion and  cochineal  tincture,  or,  if  the  acid  is  so  colored  that  the  poii\t 
of  neutralization  cannot  readily  be  decided  by  cochineal,  employ  slips  of 
turmeric  paper  (see  § 208). 

It  is  advantageous  to  use  a rather  dilute  acid,  1 c.c.=0’005  grm.  of 
nitrogen.  The  receiver  (fig.  94)  may  be  advantageously  substituted 
for  the  bulb-tube.  The  tube  a — previously  provided  with  the  caout- 
chouc stopper  b — is  first  connected  by  the  aid  of  a good  cork  with  the 
combustion  tube,  and  then  the  U-tube  c — having  been  charged  with  the 
proper  quantity  of  acid  from  a Mohr’s  burette — is  added.  At  the  ter- 
mination of  the  combustion,  when  air  has  been  drawn 
through  the  apparatus,  the  tube  a is  rinsed  into  the 
apparatus  c,  some  tincture  of  cochineal  added,  and 
standard  alkali  run  into  the  tube  from  a second  bu- 
rette, until  the  acid  is  almost  neutralized.  Now  pour 
the  contents  of  the  apparatus  into  a beaker,  rinse 
with  water,  and  complete  the  neutralization.  With 
this  receiver  neither  receding  nor  spirting  is  possible. 

By  not  pouring  out  the  fluid  till  the  point  of  satu- 
ration is  nearly  attained,  you  require  less  water  for 
rinsing  the  tube.  This  method  is  rapid  and  accu- 
rate. » 

[Iron  gas  tubes  may  be  advantageously  substi- 
tuted for  glass  tubes.  They  are  closed  at  the  rear 
with  a cork,  carrying  a bit  of  glass  tube  drawn  out 
to  a sealed  tail.  The  mixture  is  confined  to  its  place  by  loose  asbestos 
plugs.  The  corks  are  kept  from  charring  by  wrapping  the  end  of  the 
tube  with  two  or  three  thicknesses  of  filter-paper,  which  is  kept  wet  by 
a wash-flask,  or  by  dipping  the  depending  end  into  a vessel  of  water. 
The  tubes  should  be  45  cm.  long,  and  5 cm.  at  each  end  should 
project  froni  the  fire  and  be  protected  with  wet  paper. 

C.  Analysis  of  Organic  Compounds  containing  Sulphur.* 

§186. 

The  usual  method  of  determining  the  carbon  in  organic  bodies — viz., 
by  combustion  with  oxide  of  copper  or  chromate  of  lead — would  give  re- 
sults too  high  in  the  analysis  of  compounds  containing  sulphur,  since — 
more  especially  if  oxide  of  copper  is  used — a portion  of  the  sulphur 
would  be  converted  in  the  process  into  sulphurous  acid,  which  would  be 
absorbed  with  the  carbonic  acid  in  the  potash  bulbs.  Oarius  recom- 
mends to  burn  substances  containing  sulphur  in  a tube  60 — 80  cm.  long, 
with  chromate  of  lead,  care  being  taken  that  the  anterior  10 — 20  cm., 
which  contain  pure  chromate  of  lead,  are  never  heated  above  low  red- 
ness. The  chromate  of  lead  may  be  used  again  three  or  four  times 
without  refusion  ; and,  finally,  if  treated  by  Vohl’s  method  (p.  97),  it 

[*  Warren’s  method  of  determining1  carbon,  hydrogen,  and  sulphur  in  one  opera- 
tion is  described  in  Am.  Jour.  Sci.,  vol.  41,  2d  ser.,  p.  40.1 


446 


ORGANIC  ANALYSIS. 


L§  186 


is  just  as  fit  for  use  as  if  it  had  not  been  employed  for  the  combustion 
of  a substance  containing  sulphur. 

The  presence  of  sulphur  demands  no  modification  in  the  process 
described  §§  184  and  185,  for  the  determination  of  nitrogen.  In  sub- 
stances containing  oxygen  in  presence  of  sulphur,  the  oxygen  is  esti- 
mated from  the  loss. 

As  regards  the  estimation  of  the  sulphur  in  organic  compounds,  that 
element  is  invariably  weighed  in  the  form  of  sulphate  of  baryta,  into 
which  it  may  be  converted  either  in  the  dry  or  in  the  wet  way. 

a.  Methods  in  the  Dry  Way. 

1.  Method  suitable,  more  particularly , to  determine  the  sulphur  in  non- 
volatile Substances  poor  in  Sidphur , e.g.,  in  the  so-called  Protein  Com,- 
pounds  (v.  Liebig). 

Put  some  lumps  of  hydrate  of  potassa,  free  from  sulphuric  acid  (§  66, 

6.  c),  into  a capacious  silver  dish,  add  J of  pure  nitrate  of  potassa,  and 
fuse  the  mixture,  with  addition  of  a few  drops  of  water.  When  the  mass 
is  cold,  add  to  it  a weighed  quantity  of  the  finely  pulverized  substance, 
fuse  over  the  lamp,  stir  with  a silver  spatula,  and  increase  the  heat,  con- 
tinuing the  operation  until  the  color  of  the  mass  shows  that  the  carbon 
separated  at  first  has  been  completely  consumed.  Should  this  occupy 
too  much  time,  you  may  accelerate  it  by  the  addition  of  nitrate  of 
potassa  in  small  portions.  Let  the  mass  cool,  then  dissolve  in  water, 
supersaturate  the  solution  with  hydrochloric  acid  in  a capacious  beaker 
covered  with  a glass  dish,  and  precipitate  with  chloride  of  barium. 
Wash  the  precipitate  well  with  boiling  water,  first  by  decantation,  then 
on  the  filter.  I)ry  and  ignite.  Treat  the  ignited  sulphate  of  baryta  as 
directed  p.  265  ; if  this  latter  operation  is  omitted,  the  result  is  almost 
always  too  high. 

2.  Method  adapted  more  particularly  for  the  Analysis  of  non-volatile 
or  difficultly  volatile  Substances  containing  more  than  5 per  cent,  of  Sul- 
phur. (Kolbe*). 

Introduce  into  the  posterior  part  of  a straight  combustion  tube,f  40 — 
45  cm.  long,  a layer,  7 — 8 cm.  long,  of  an  intimate  mixture  of  8 parts 
of  pure  anhydrous  carbonate  of  soda,  and  1 part  of  pure  chlorate  of  * 
potassa ; after  this  introduce  the  weighed  substance,  then  another 
layer,  7 or  8 cm.  long,  of  the  same  mixture ; mix  the  organic  compound 
intimately  with  the  carbonate  of  soda  and  chlorate  of  potassa,  by  means 
of  the  mixing  wire  (fig.  76,  p.  426)  ; fill  up  the  still  vacant  part  of  the 
tube  with  anhydrous  carbonate  of  soda  or  potassa  mixed  with  a little 
chlorate  of  potassa.  Clear  a wide  passage  from  end  to  end  by  a few  gen- 
tle taps,  place  the  tube  in  a combustion  furnace,  heat  the  anterior  part 
to  redness,  and  then,  progressing  slowly  toward  the  posterior  part,  pro- 
ceed to  surround  with  red-hot  charcoal  the  part  occupied  by  the  mix- 
ture. In  the  analysis  of  substances  abounding  in  carbon,  it  is  advisable  to 
introduce  into  the  posterior  part  of  the  tube  a few  lumps  of  pure  chlorate 
of  potassa,  to  insure  complete  combustion  of  the  carbon,  and  perfect 
conversion  into  sulphates  of  the  compounds  of  potassa  with  the  lower 
oxides  of  sulphur  that  may  have  formed.  The  sulphuric  acid  in  the  con- 
tents of  the  tube  is  determined  as  in  1. 


* Supplemente  zum  Handworterbuch.  205. 
f Sealed  and  rounded  at  the  end  like  a test  tube. 


ORGANIC  ANALYSIS. 


447 


§ 186.] 

3.  Method  adapted  for  the  Analysis  both  of  non-volatile  and  volatile 
Substances , but  more  especially  the  latter  (Debus*). 

Dissolve  1 eq.  (149  parts)  of  bichromate  of  potassa  purified  by  recrys- 
tallization, and  2 eq.  of  carbonate  of  soda  (106  parts)  in  water,  evapo- 
rate the  solution  to  dryness,  reduce  the  lemon-colored  saline  mass  (KO, 
CrOg  + NaO,  Cr03-f-NaO,  C02)  to  powder,  heat  to  intense  redness  in  a 
Hessian  crucible,  and  transfer  still  hot  to  a filling-tube  (fig.  75,  p. 
426). f When  the  powder  is  cold,  introduce  a layer  of  it,  7 — 10  cm. 
long,  into  a common  combustion  tube  ; then  introduce  the  substance,  and 
after  this  another  layer,  7 — 10  cm.  long,  of  the  powder.  Mix  inti- 
mately by  means  of  the  mixing  wire,  then  fill  the  still  unoccupied  part 
of  the  tube  with  the  saline  mixture,  and  apply  heat  as  in  an  ordinary 
ultimate  analysis.  When  the  entire  mass  is  heated  to  redness,  conduct 
a slow  stream  of  dry  oxygen  gas  over  it  for  \ — 1 hour.  When  cold, 
wipe  the  ash  off  the  tube,  cut  the  latter  into  several  pieces  over  a sheet 
of  paper,  and  treat  them  in  a beaker  with  a sufficient  quantity  of  water 
to  dissolve  the  saline  mass.  Add  hydrochloric  acid  in  tolerable  excess, 
then  some  alcohol,  and  apply  a gentle  heat  until  the  solution  shows  a 
beautiful  green  color ; filter  oft’  the  sesquioxide  of  chromium  produced 
by  the  combustion  (this  contains  sulphuric  acid) ; wash  first  with  water 
containing  hydrochloric  acid,  then  with  alcohol,  dry,  and  transfer  to  a 
platinum  crucible ; add  the  filter-ash,  mix  with  1 part  of  chlorate 
and  2 parts  of  carbonate  of  potassa  (or  soda),  and  ignite  until  the  ses- 
quioxide of  chromium  is  completely  converted  into  alkaline  chromate. 
Dissolve  the  fused  mass  in  dilute  hydrochloric  acid,  and  reduce  by  heating 
with  alcohol ; add  the  solution  to  the  fluid  filtered  from  the  sesquioxide 
of  chromium,  heat  the  mixture  to  boiling,  and  precipitate  the  sulphuric 
acid  with  chloride  of  barium.  Debus’s  test-analyses  were  very  satis- 
factory; thus  he  obtained  99*76  and  99*50  of  sulphur  for  100,  again 
30*2  of  sulphur  in  xanthogenamide  for  30*4,  &c. 

4.  Method  equally  adapted  for  the  Analysis  of  Solid  and  Liquid 
Volatile  Compounds.  (W.  J.  Russell  suggested  by  Bunsen.) 

Introduce  into  a combustion  tube,  40  cm.  long,  sealed  at  the  posterior 
end,  first  2 — 3 grm.  pure  oxide  of  mercury,  then  a mixture  of  equal 
parts  of  oxide  of  mercury  and  pure  anhydrous  carbonate  of  soda,  mixed 
with  the  substance,  and  fill  up  the  tube  with  carbonate  of  soda  mixed 
with  a little  oxide  of  mercury.  Connect  the  open  end  of  the  tube  with 
a gas  delivery  tube  dipping  under  water,  to  effect  the  condensation  of  the 
mercurial  fumes.  Place  a screen  in  front  of  the  part  of  the  tube  occu- 
pied by  the  substance,  then  heat  the  anterior  part  to  bright  redness,  and 
maintain  this  temperature  during  "the  entire  process.  At  the  same 
time,  heat  another  portion  of  the  tube,  nearer  to  the  end,  but  not  to  the 
same  degree  of  intensity,  so  that  there  may  be  alternate  parts  in  the 
tube  in  which  the  oxide  of  mercury  is  left  undecomposed.  When  the 


* Annal.  d.  Chem.  u.  Pharm.  76,  90. 

\ The  saline  mass  must  always  first  be  tested  for  sulphur.  For  this  purpose 
a small  portion  of  it  is  reduced  with  hydrochloric  acid  and  alcohol,  chloride  of 
barium  added,  and  the  mixture  allowed  to  stand  12  hours  at  rest.  No  trace  of 
a precipitate  should  be  discernible. 

\ Quart.  Joum.  Chem.  Soc.  7,  212. 


448 


ORGANIC  ANALYSIS. 


[§  187. 


part  before  the  screen  is  at  bright  redness,  remove  the  screen,  heat  the 
mixture  containing  the  substance,  regulating  the  application  of  heat 
so  as  to  insure  complete  decomposition  in  the  course  of  10 — 15  minutes, 
and  heat  at  the  same  time  the  still  unheated  parts  of  the  tube,  and 
lastly  also  the  pure  oxide  of  mercury  at  the  extreme  end.  The  gas  must 
be  tested  from  time  to  time,  to  ascertain  whether  it  contains  free  oxygen. 
Dissolve  the  contents  of  the  tube  in  water,  add  some  chloride  of  mer- 
cury, to  decompose  the  sulphide  of  sodium  which  may  have  formed, 
acidify  the  hydrochloric  acid,  oxidize  the  sulphide  of  mercury  which 
may  have  formed  with  chlorate  of  potassa,  and  finally  precipitate  the 
sulphuric  acid  with  chloride  of  barium.  W.  J.  Russell  obtained  by 
this  method  very  satifactory  results  in  the  analysis  of  pure  sulphur, 
sulphocyanide  of  potassium,  and  bisulphide  of  carbon. 

b.  Method  in  the  Wet  Way* 

According  to  Rivot,  Beudant,  and  Daguin,!  the  sulphur  in  organic 
compounds  may  be  readily  determined  by  heating  with  pure  solution  of 
potassa,  adding  2 volumes  of  water  and.  conducting  chlorine  into  the 
fluid.  When  the  oxidation  is  effected,  the  solution  is  acidified  and  freed 
from  the  excess  of  chlorine  by  apjdication  of  heat,  then  filtered, 
and  the  filtrate  precipitated  by  chloride  of  barium.  Mr.  C.  J.  Merz, 
in  my  laboratory,  has  employed  both  this  method  and  v.  Liebig’s  (a,  1) 
in  the  analysis  of  fine  horn  shavings.  The  process  appears  convenient 
and  exact.  | 

Substances  leaving  an  ash  on  incineration,  and  which  may  therefore 
be  presumed  to  contain  sulphates,  are  boiled  with  hydrochloric  acid  ; 
the  solution  obtained  is  filtered,  and  the  filtrate  tested  with  chloride  of 
barium.  If  a precipitate  of  sulphate  of  baryta  forms,  the  sulphur  con- 
tained in  it  is  deducted  from  the  quantity  found  by  one  of  the  methods 
described  above ; the  difference  gives  the  quantity  of  the  sulphur  which 
the  analyzed  substance  contains  in  organic  combination. 

D.  Determination  of  Phosphorus  in  Organic  Compounds. 

§ 187. 

Mulder,  who  has  occupied  himself  much  with  the  determination 
of  phosphorus  in  organic  substances,  recommends  the  following  me- 
thod : — 

Dissolve  a weighed  portion  of  the  substance  by  boiling  with  hydro- 
chloric acid;  filter,  if  necessary,  and  determine  the  phosphoric  acid 
which  the  fluid  may  contain,  by  Berthier’s  method  (§  134,  I.,  d ). 
Boil  another  weighed  portion  of  the  substance  with  nitric  acid,  and 
treat  the  fluid  in  the  same  way  as  the  hydrochloric  acid  solution.  If 
you  find  in  both  cases  the  same  percentage  of  phosphoric  acid,  the 
substance  contains  the  phosphorus  only  in  the  form  of  phosphoric 
acid  ; but  if  you  obtain  a larger  proportion  of  acid  in  the  second 
experiment  than  in  the  first,  the  difference  indicates  the  quantity 
of  phosphoric  acid  formed  by  the  action  of  the  nitric  acid  upon 

[*  For  the  excellent  processes  of  Carius,  see  Anna!,  d.  Chem  u.  Pharm.  116, 

11.1 

f Comp.  rend.  37,  835  ; Journ.  f.  prakt.  Chem.  61,  135. 

i Two  experiments  were  made  with  each  method,  on  horn  dried  at  100°. 
The  percentages  obtained  were  as  follows: — By  v.  Liebig’s  method,  3 37  and 
3 '345  ; by  the  present  method,  3 '31  and  3 33. 


§ 188.] 


ORGANIC  ANALYSIS. 


449 


phosphorus  contained  in  the  analyzed  compound  in  the  unoxidized 
state. 

The  phosphorus  cannot  be  determined  by  incineration  of  the  sub- 
stance and  examination  of  the  ash.  Vitellin,  which,  when  treated  with 
nitric  acid,  gives  3 per  cent,  of  phosphoric  acid,  yields  barely  0*3  per 
cent,  of  ash  (v.  Baumhauer). 

The  methods  described  in  § 186,  g,  1,  2,  4,  and  6,  may  also  be  em- 
ployed to  determine  the  total  quantity  of  phosphorus  in  organic  sub- 
stances. 

E.  Analysis  of  Organic  Substances  containing  Chlorine, 
Bromine,  or  Iodine. 

§ 188. 

Substances  containing  Bromine  and  Iodine  are  analyzed  generally  in 
the  same  manner  as  those  containing  Chlorine. 

Those  portions  of  the  following  § which  are  enclosed  between  square 
brackets  refer  exclusively  to  combinations  of  Iodine  or  Bromine , as  the 
case  may  be. 

The  combustion  of  organic  substances  containing  chlorine  with  oxide 
of  copper  gives  rise  to  the  formation  of  subchloride  of  copper,  which, 
were  the  process  conducted  in  the  usual  manner,  would  condense  in  the 
chloride  of  calcium  tube,  and  would  thus  vitiate  the  determination  of 
the  hydrogen.  This  and  every  other  error  may  be  prevented  by  the 
employment  of  chromate  of  lead  (§  177).  The  chlorine  is,  in  that  case, 
converted  into  chloride  of  lead,  and  retained  in  that  form  in  the  com- 
bustion tube. 

If  the  combustion  is  effected  with  oxide  of  copper  in  a current  of 
oxygen,  the  subchloride  of  copper  is  decomposed  by  the  oxygen,  oxide 
of  copper  and  free  chlorine  being  formed  ; the  latter  is  retained  partly 
in  the  chloride  of  calcium  tube,  partly  in  the  potash  bulbs.  To 
remedy  this  defect,  Staedeler  * proposes  to  fill  the  anterior  part  of  the 
tube  with  clean  copper  turnings ; these  must  be  kept  red-hot  during  the 
combustion,  and  the  current  of  oxygen  must  be  arrested  the  moment 
they  begin  to  oxidize.  K.  Kraut  f observes  with  reference  to  this  pro- 
cess that  it  is  well  to  place  a roll  of  silver  foil,  about  5 inches,  long,  in 
front  of  the  layer  of  metallic  copper.  In  the  absence  of  the  silver  the 
transmission  of  oxygen  has  to  be  conducted  with  caution,  in  order 
that  no  chlorine  may  be  expelled  from  the  subchloride  of  copper  first 
formed,  but  by  adopting  Kraut’s  recommendation  we  may  continue 
passing  the  gas  without  fear  till  it  escapes  free  from  the  potash  tube. 
[In  the  case  of  substances  containing  iodine,  it  is  needless  to  employ  me- 
tallic copper  as  well  as  silver  foil.]  The  silver  may  be  used  over  and 
over  again,  but  at  last  requires  ignition  in  a stream  of  hydrogen.  Ac- 
cording to  A.  Volcker,|  the  evolution  of  chlorine  may  be  prevented  by 
mixing  the  oxide  of  copper  with  i oxide  of  lead. 

[In  the  analysis  of  bodies  containing  bromine  the  above  methods  do 
not  always  answer,  v.  Gorup-Besanez  ||  satisfied  himself  of  this  by 
analyzing  dibromotyrosin.  Whether  this  body  was  burnt  with  chro- 
mate of  lead,  with  a mixture  of  chromate  of  lead  and  chromate  of  potash, 

* Anna!  d.  Chem.  u.  Pharm.  69,  335.  f Zeitschrift  f.  analyt.  Chem.  2,  242. 

X Chem.  Gaz.  1849,  245.  29.  ||  Zeitschrift  f.  analyt.  Chem.  1,  439. 

29 


450 


ORGANIC  ANALYSIS. 


[§  1 88. 

with  oxide  of  copper  and  oxygen  and  an  anterior  layer  of  chromate  of 
lead,  with  an  anterior  layer  of  copper  turnings,  whether  mixed  or  in 
the  platinum  boat,  in  whichever  way  the  analysis  was  performed  the 
carbonic  acid  always  came  out  several  per-cents  too  low,  because 
metallic  bromide  was  formed,  which  fused  and  enclosed  carbon,  thereby 
preventing  its  oxidation.  The  following  process,  on  the  contrary, 
yielded  good  results  : — Into  a combustion  tube  drawn  out  to  a long 
point,  introduce  first  a three-inch  layer  of  oxide  of  copper,  then  a plug 
of  asbestos,  then  a mixture  of  the  substance  (finely  powdered)  with 
about  an  equal  weight  of  well-dried  oxide  of  lead  in  a porcelain  boat ; 
again  a plug  of  asbestos,  then  granulated  oxide  of  copper,  then  chromate 
of  lead  or  copper  turnings.  First  heat  the  anterior  and  then  the  pos- 
terior layers  to  ignition,  and  warm  the  part,  where  the  boat  is,  very 
cautiously  and  gradually : everything  combustible  distils  over,  arrives 
at  the  oxide  of  copper  in  the  form  of  vapor,  and  is  there  burnt.  In 
the  boat  nothing  remains  but  a mixture  of  bromide  and  oxide  of  lead. 
Complete  the  combustion  with  oxygen,  taking  care  not  to  heat  the  point 
where  the  boat  is  too  strongly,  nor  continue  the  transmission  of  oxygen 
longer  than  necessary.  Observe  also  that  no  bromide  of  copper  sub- 
limes into  the  chloride  of  calcium  tube.] 

As  regards  the  determination  of  the  chlorine  itself  ’ this  is  usually 
effected  either  ( a ) by  igniting  the  substance  with  alkalies  or  alkaline 
earths,  by  which  process  all  the  chlorine  is  obtained  as  chloride,  or  (6) 
by  oxidizing  the  substance  with  nitric  acid,  &c.,  in  a sealed  tube. 

a.  As  chlorine-free  lime  is  easily  obtainable  (by  burning  marble),  this 
body  is  usually  preferred  to  effect  the  decomposition.  It  must  always 
be  tested  for  chlorine  previous  to  use. 

Introduce  into  a combustion  tube,  about  40  cm.  long,  the  posterior 
end  of  which  is  sealed  and  rounded  like  a test  tube,  a layer  of  lime,  6 
cm.  long,  then  the  substance,  after  this  another  layer  of  lime,  6 cm. 
long,  and  mix  with  the  wire ; fill  the  tube  almost  to  the  mouth  with 
lime,  clear  a free  passage  for  the  evolved  gases  by  a few  gentle  taps, 
and  apply  heat  in  the  usual  way.  Yolatile  fluids  are  introduced  into 
the  tube  in  small  glass  bulbs.  When  the  decomposition  is  terminated, 
dissolve  in  dilute  nitric  acid,  and  precipitate  with  solution  of  nitrate  of 
silver  (§  141).  Kolbe  recommends  the  following  process  to  obtain 
the  contents  of  the  combustion  tube  : — When  the  decomposition  is  com- 
pleted, remove  the  charcoal,  insert  a cork  into  the  open  end  of  the  tube, 
remove  every  particle  of  ash,  and  immerse  the  tube,  still  hot,  with  the 
sealed  end  downwards,  into  a beaker  filled  two-thirds  with  distilled 
water ; the  tube  breaks  into  many  pieces,  and  the  contents  are  then  more 
readily  acted  upon.  As  in  this  method  the  ignition  of  compounds  abound- 
ing in  nitrogen  may  be  attended  with  formation  of  cyanide  of  calcium  or 
cyanide  of  sodium,  the  separation  of  the  chloride  and  the  cyanide  of  sil- 
ver, if  required,  is  to  be  effected  by  the  process  given  in  § 169,  6,  b 
(Neubauer  and  Kerner  *).  In  the  analysis  of  acid  organic  compounds 
containing  chlorine  ^(e.  <7.,  chlorospiroylic  acid),  the  chlorine  may  often 
be  determined  in  a simpler  manner,  viz.,  by  dissolving  the  substance 
under  examination  in  an  excess  of  dilute  solution  of  potassa,  evapora- 
ting to  dryness,  and  igniting  the  residue,  by  which  means  the  whole  of 
the  chlorine  present  is  converted  into  a soluble  chloride  (Lowig). 


* Anna!,  d.  Chem.  ,u.  Pharm.  101,  324,  344. 


ORGANIC  ANALYSIS. 


451 


§ 189.] 

b.  In  more  readily  decomposable  compounds,  e . g.y  in  the  substitution 
products  of  acids,  the  halogen  may  also  be  determined  by  decomposing 
the  substance  by  contact  during  several  hours  with  water  and  sodium 
amalgam,  acidifying  the  fluid  with  nitric  acid,  and  precipitating  with  sil- 
ver solution  (Kekule  *). 


F.  Analysis  of  Organic  Compounds  containing  Inorganic  Bodies. 

§ 189. 

In  the  analysis  of  organic  compounds  containing  inorganic  bodies,  it 
is,  of  course,  necessary  first  to  ascertain  the  quantity  of  the  latter  before 
proceeding  to  the  determination  of  the  carbon,  &c.,  as  otherwise  the 
amount  of  the  organic  body  whose  constituents  have  furnished  the  car- 
bonic acid,  water,  &c.,  not  being  known,  it  would  be  impossible  to  esti- 
mate the  oxygen  from  the  loss. 

If  the  substances  in  question  are  salts  or  similar  compounds,  their 
bases  are  determined  by  the  methods  given  in  the  Fourth  Section  ; but 
in  cases  where  the  inorganic  bodies  are  of  a nature  to  be  regarded  more 
or  less  as  impurities  (e.^.,  the  ash  in  coal),  they  may  usually  be  deter- 
mined with  sufficient  accuracy  by  the  combustion  of  a weighed  portion 
of  the  substance  in  an  obliquely  placed  platinum  crucible,  or  in  a plati- 
num dish.  In  the  analysis  of  substances  containing  fusible  salts,  even 
long-continued  ignition  will  often  fail  to  effect  complete  combustion,  as 
the  carbon  is  protected  by  the  fused  salt  from  the  action  of  the  oxy- 
gen. In  such  cases,  the  best  way  to  effect  the  purpose  is  to  carbonize 
the  substance,  treat  the  mass  with  water,  and  incinerate  the  undissolved 
residue  ; the  aqueous  solution  is,  of  course,  likewise  evaporated  to  dry- 
ness, and  the  weight  of  the  residue  added  to  that  of  the  ash. 

If  organic  compounds  whose  ash  contains  potassa,  soda,  baryta,  lime, 
or  strontia,  are  burnt  with  oxide  of  copper,  part  of  the  carbonic  acid 
evolved  remains  combined  with  the  bases.  As,  in  many  cases,  the  amount 
of  carbonic  acid  thus  retained  is  not  constant,  and  the  results  are,  more- 
over, more  accurate  if  the  whole  amount  of  the  carbon  is  expelled  and 
weighed  as  carbonic  acid,  the  combustion  is  effected  with  chromate  of 
lead,  with  addition  of  ^ of  bichromate  of  potassa,  according  to  the  di- 
rections given  in  § 177.  Accurate  experiments  have  shown  that  in  this 
case  not  a trace  of  carbonic  acid  remains  with  the  bases. 

If  the  substance  is  weighed  in  a porcelain  or  platinum  boat,  and  the 
combustion  is  effected  according  to  § 178,  the  ash,  carbon,  and  hydrogen 
may  be  determined  in  one  portion.  The  amount  of  carbonic  acid  con- 
tained in  the  ash  is  added  to  that  found  by  the  process  of  combustion ; 
if  the  carbonic  acid  in  the  ash  cannot  be  calculated,  as  in  the  case  of  car- 
bonates of  the  alkalies,  it  may  be  determined  by  means  of  fused  borax 
(§  139,  II.,  e). 

In  burning  substances  containing  mercury,  the  arrival  of  any  of  the 
metal  at  the  chloride  of  calcium  tube  may  be  prevented  by  having  a layer 
of  copper-turnings  in  the  anterior  part  of  the  combustion  tube,  and  by 
not  allowing  the  foremost  portion  to  get  too  hot. 


* Jahresb.  v.  Kopp.  u.  Will.  1861,  832. 


452  ORGANIC  ANALYSIS.  [§  190. 

III.  Determination  of  the  Equivalent  of  Organic  Compounds. 

The  methods  of  determining  the  equivalent  of  organic  compounds  dif- 
fer essentially  according  to  the  properties  of  the  various  compounds. 
There  are  three  general  methods  in  use  for  this  purpose,  which  I will 
proceed  to  describe. 


190. 


1.  We  ascertain  the  amount  of  a Body  of  known  Equivalent , which 
forms  a well-characterized  Compound  with  the  Substance  whose  Equiva- 
lent is  to  be  determined. 

This  method  is  pursued  in  determining  the  equivalent  of  the  organic 
acids  and  organic  bases,  and  of  many  indifferent  bodies  possessed  of  the 
property  of  combining  wdth  bases  or  acids.  We  occupy  ourselves  here 
simply  with  the  process ; the  mode  of  calculating  the  equivalent  from 
the  results  obtained  will  be  found  under  “ The  Calculation  of  Analy- 
ses.” 

a.  The  equivalent  of  organic  acids  is,  in  most  cases,  determined  from 
the  silver  salt,  because  the  analysis  of  this  is  very  simple,  and  there  is 
almost  always  the  positive  certainty  that  the  analyzed  salt  is  not  a basic 
or  hydrated  compound.  Other  salts  also  are,  however,  frequently  used 
for  the  same  purpose,  particularly  those  of  lead,  baryta,  and  lime.  (In 
the  analysis  of  the  lead  salts,  especial  care  must  be  taken  not  to  mistake 
basic  for  neutral,  nor  in  the  analysis  of  the  baryta  and  lime  salts,  hy- 
drated for  anhydrous  salts.)  For  the  manner  in  which  the  determina- 
tion of  the  bases  in  question  is  effected,  I refer  to  Section  IV. 

b.  The  equivalent  of  organic  bases  forming  well-crystallizable  salts 
with  sulphuric,  hydrochloric,  or  any  other  easily  determined  acid,  is  best 
ascertained  by  estimating,  by  the  usual  methods,  the  acid  contained  in 
a weighed  amount  of  the  salt. 

If  the  salts  do  not  crystallize,  a known  quantity  of  the  dry  alkaloid  is 
(after  v.  Liebig)  introduced  into  a drying  tube 
= (fig.  95),  which  is  then  accurately  weighed  with 
its  contents  ; a slow  current  of  dry  hydrochloric 
acid  gas  is  transmitted  through  the  apparatus  for 
some  time ; the  tube  ultimately  heated  to  100° 
(see  p.  38,  fig.  21),  and  a stream  of  atmospheric  air 
transmitted  through  it ; the.  quantity  of  the  hy- 
drochloric acid  absorbed  is  found  from  the  increase 
in  the  weight  of  the  tube.  The  accuracy  of  the  results  may  be  controlled 
by  dissolving  the  hydrochlorate  in  water,  and  precipitating  the  chlorine 
from  the  solution  by  nitrate  of  silver.  The  equivalent  of  the  alkaloids 
may  be  determined  also  from  the  insoluble  double  salts  produced  by  pre- 
cipitating the  solution  of  their  hydrochlorates  with  bichloride  of  plati- 
num; the  double  chlorides  thus  produced  are  cautiously  ignited  (§  124), 
and  the  residuary  platinum  weighed. 

c.  In  the  case  of  indifferent  bodies , there  is  usually  no  choice  about 
the  matter,  and  we  have  to  determine  the  equivalent  from  the  lead  com- 
pound ; since  many  of  these  substances  either  altogether  refuse  to  enter 
into  combination  with  other  bases  besides  lead,  or  only  form  with  them 
compounds  which  cannot  be  obtained  in  a state  of  purity.  Although  the 
determination  of  the  equivalent  of  an  indifferent  body  from  the  compound 


Fix.  95. 


ORGANIC  ANALYSIS. 


453 


§ 191.] 

which  the  latter  forms  with  lead  is  liable  to  leave  the  matter  in  doubt, 
as  the  oxide  of  lead  will  often  combine  with  such  substances  in  varying 
proportions,  yet  the  analysis  of  such  compounds  is  always  interesting  in 
this — that  we  learn  by  it  whether  the  organic  body  combines  with  the 
oxide  of  lead  without  alteration,  or  gives  up  water  upon  entering  into 
combination. 

Organic  substances  will  also  occasionally  form  with  water  solid  and 
crystallizable  compounds,  by  the  analysis  of  which  the  equivalent  of  the 
organic  body  may  be  determined. 

§ 191. 

2.  The  Specific  Gravity  of  the  Vapor  of  the  Compound  is  deter- 
mined. 

Of  the  numerous  methods  which  have  been  proposed  for  the  accom- 
plishment of  this  object,  I shall  describe  only  those  two  which  are  more 
frequently  employed  in  laboratories  as  the  simplest  and  most  suitable. 
In  all  determinations  of  vapor  densities  it  is  necessary  that  the  tempera- 
ture at  which  they  are  made  should  be  sufficiently  raised  (at  least  30 — 40° 
above  the  boiling  point  of  the  substances),  so  that  the  vapor  may  pos- 
sess the  coefficient  of  expansion  of  the  gases.  The  extreme  importance 
of  this  rule  is  evident  from  the  fact  that  at  temperatures  only  slightly 
above  the  boiling  point  higher  densities  are  found,  the  densities  decreas- 
ing with  the  increase  of  temperature,  and  becoming  constant  only  after 
a certain  point. 

A.  Process  of  Dumas. 

The  following  are  the  outlines  of  this  method  : — A light  glass  globe, 
filled  with  dry  air,  and  the  exact  capacity  of  which  is  afterwards  ascer- 
tained, is  accurately  weighed ; the  weight  of  the  air  in  the  globe  is  cal- 
culated at  the  temperature  and  atmospheric  pressure  observed  during 
the  process  of  weighing,  and  the  result  subtracted  from  the  first  weight : 
the  difference  expresses  the  weight  of  the  exhausted  vessel.  A more 
than  sufficient  quantity  of  the  substance,  the  density  of  the  vapor  of 
which  it  is  intended  to  determine,  is  then  introduced  into  the  globe,  and 
exposed  to.  a uniform  temperature  sufficiently  above  the  boiling  point 
of  the  substance,  until  the  latter  is  completely  converted  into  vapor, 
and  the  excess  expelled,  together  with  the  atmospheric  air  originally 
contained  in  the  globe ; the  vessel  is  then  sealed  air-tight,  and  weighed. 
The  difference  between  the  weight  found  and  that  of  the  exhausted 
globe,  expresses  the  weight  of  a given  volume  of  the  vapor ; supplying 
thus  the  necessary  data  for  calculating  its  specific  gravity. 

It  is  hardly  necessary  to  remark  that  the  volume  of  the  air  and  the 
vapor  must  be  reduced  to  the  same  pressure  and  temperature,  and  con- 
sequently that  the  state  of  the  barometer  and  thermometer  must  be 
noted  both  during  the  first  weighing  and  at  the  time  of  sealing  the  glass 
globe. 

This  method  is  of  course  applicable  only  to  substances  which  volatilize 
without  suffering  decomposition.  To  obtain  accurate  results,  it  is  indis- 
pensable that  the  substance  be  perfectly  pure. 

I will  now  proceed  to  describe  the  process  ; for  the  manner  of  correct- 
ing and  calculating  the  results,  and  inferring  from  them  the  composition 
of  the  bodies  examined,  I refer  to  § 204. 


454 


ORGANIC  ANALYSIS. 


[§  191. 


a.  Apparatus  and  other  Requisites. 

1.  The  Substance. — From  6 to  8 grammes  are  required, 
point  must  be  pretty  accurately  known. 


The  boiling 


2.  A light  Glass  Globe  with  drawn-out  Neck. 

An  ordinary  globe  of  pure  glass  is  selected,  free  from  flaws  and  holding 
from  250  to  500  c.  c. ; it  is  carefully  rinsed  with  water,  and  then  thoroughly 
dried.  After  this,  it  is  completely  exhausted,  dry  air  readmitted  into  it, 
and  the  same  operation  repeated.  The  neck  of  the  globe  is  then  softened 
near  the  bulb,  and  drawn  out  in  the  shape  represented  in  fig.  96. 

The  extreme  point  is  cut  off,  and  the  edges  slightly 
rounded  over  the  spirit-lamp.  (This  point  having  to  be 
sealed  air-tight  with  the  greatest  despatch,  at  a subse- 
quent stage  of  the  process,  it  is  advisable  to  ascertain,  in 
the  first  place,  whether  the  glass  of  the  globe  is  readily 
fusible  or  not ; this  may  be  done  by  trying  to  seal  the 
point  on  the  original  neck  of  the  balloon ; should  this 
present  any  difficulty,  the  globe  is  unfit  for  the  intended 
purpose.) 

3.  A small  Iron  or  Copper  Vessel  for  the  reception 
of  the  fluid  in  which  the  globe  is  to  be  heated  (see  fig. 
97).  The  fluid  which  is  to  serve  as  bath  must  admit  of  being  heated  to  at 
least  30 — 40°  beyond  the  boiling  point  of  the  substance  under  examina- 
tion. Oil  will  answer  the  purpose  in  nearly  all  cases  where  a tempera- 
ture higher  than  that  of  boiling  water  is  required  ; however,  a chloride  of 
calcium  bath — if  its  temperature,  which  in  a perfectly  saturated  bath  may 
be  raised  to  180°,  is  sufficiently  high  for  the  purpose — is  more  convenient 
than  an  oil-bath,  as  the  globe  may  be  more  easily  cleaned. 

4.  An  Apparatus  to  keep  the  Globe  in  Position. — This  may  be 
readily  made  with  a handle  and  some  iron  wire.  During  the  operation, 
it  is  attached  to  a retort-stand  (see  fig.  97). 

5.  A quantity  of  Mercury  more  than  sufficient  to  fill  the  globe. 

6.  A graduated  Tube  of  about  100  c.  c.  capacity. 

7.  A Gas-  or  Spirit-lamp  and  Blowpipe. 

8.  A correct  Barometer. 

9.  A correct  Thermometer,  oapable  of  indicating  the  highest  degree  of 
heat  the  case  under  examination  may  require. 


b.  The  Process. 

a.  Weigh  the  globe,  placing  a thermometer  inside  the  case  of  the 
balance.  Leave  the  globe  for  ten  minutes  on  the  scale,  to  ascertain 
whether  its  weight  remains  constant.  If  so,  the  weight  is  noted,  together 
with  the  height  of  the  barometer,  and  the  temperature  indicated  by  the 
thermometer  inside  the  case. 

/?.  Heat  the  globe  gently,  and  dip  the  point  deep  into  about  8 grm.  of 
the  substance,  which,  if  solid,  must  have  been  liquefied  by  the  application 
of  a gentle  heat.  (If  the  substance  under  examination  has  a high  fusing 
point,  the  neck  and  point  of  the  globe  likewise  require  heating,  to  guard 
against  the  fluid  solidifying  too  soon.)  When  the  globe  has  cooled — 
which,  in  the  case  of  very  volatile  substances,  is  to  be  accelerated  by  drop- 
ping ether  upon  it — the  fluid  enters  and  spreads  in  it.  Do  not  introduce 
more  than  5 — 7 grm. 


ORGANIC  ANALYSIS. 


455 


§ 191-1 


y.  Heat  the  contents  of  the  vessel  3 to  from  40  to  50°,  and  immerse 
the  globe  by  means  of  the  apparatus  4,  and  also  a thermometer,  in  the 
bath,  as  shown  in  fig.  97. 

Raise  the  temperature  of  the 
bath  to  between  30  and  40° 
above  the  boiling  point  of  the 
substance.*  As  soon  as  the  tem- 
perature in  the  globe  is  some- 
what higher  than  the  boiling 
point  of  the  substance,  the  vapor 
of  the  latter  rushes  out  through 
the  orifice  of  the  neck  ; the  force 
of  the  current  increases  at  first 
with  the  temperature  of  the  bath, 
but  diminishes  afterwards  by 
degrees,  and  finally  (after  about 
15  minutes)  ceases  altogether. 

Should  any  of  the  vapor  have 
condensed  into  drops  in  the  point 
of  the  neck  projecting  out  of 
the  bath,  these  may  be  at  once  reconverted  into  vapor,  by  moving  a piece 
of  red-hot  charcoal  to  and  fro  under  it.  The  moment  that  a perfect 
equilibrium  is  fully  established  at  the  desired  temperature,  seal  the  point 
of  the  globe,  by  means  of  a spirit-lamp  and  blowpipe,  and  note  immediate- 
ly after  the  height  of  the  thermometer.  To  ascertain  whether  or  not  the 
point  is  hermetically  sealed,  you  need  simply  direct  a current  of  air 
through  the  blowpipe  upon  the  projecting  point  of  the  neck  : if  the  tube 
is  closed  hermetically,  a small  portion  of  the  vapor  condenses,  forming  a 
column  of  fluid,  which  is  retained  in  the  end  of  the  tube  by  capillary 
attraction  ; this  is  not  observed  if  the  tube  is  not  hermetically  sealed. 
The  height  of  the  barometer  also  is  noted  again,  if  it  has  changed  since 
the  first  observation. 

5.  Remove  the  sealed  globe  from  the  bath,  allow  to  cool,  wash  most 
carefully,  wipe  perfectly  dry,  and  weigh  again  in  the  same  manner  as 
before. 

s.  Immerse  the  pointed  end  of  the  globe  in  its  entire  length  in  mercury, 
scratch  a mark  with  a file  near  the  end,  and  break  oft'  the  point ; where- 
upon the  mercury  will  immediately  rush  into  the  globe,  a vacuum  having 
been  created  in  it  by  the  condensation  of  the  vapor.  (In  this  operation, 
place  the  glass  globe  in  the  hollow  of  your  hand,  and  rest  the  latter  upon 
the  edge  of  the  mercurial  trough.)  If  the  globe,  at  the  moment  of  seal- 
ing, was  perfectly  free  from  air,  it  will  fill  completely  with  mercury  ; 
otherwise,  an  ai^-bubble  will  remain  in  it.  In  either  case  transfer  the 
mercury  from  the  globe  to  the  graduated  tube  (6),  and  measure  accurately ; 
if  there  was  air  in  the  globe  at  the  moment  of  sealing  it,  fill  it  now  with 
water,  and  measure  also  the  volume  of  the  latter  liquid  : the  difference 
between  the  volume  of  the  mercury  and  that  of  the  water  shows  the 
volume  of  the  air  which  had  remained  in  the  globe. 

This  method,  if  properly  executed,  gives  nearly  accurate  results  ; for 
the  manner  of  calculating  the  latter,  I refer  to  § 201. 


Fig.  97. 


* If  a chloride  of  calcium  or  oil -bath  is  used,  you  must  endeavor  to  maintain 
a uniform  temperature  towards  the  end  of  the  process,  which  may  be  easily 
effected  by  properly  regulating  the  heat. 


456  ORGANIC  ANALYSIS.  [§  191. 

B.  Process  of  Gay-Lussac. 

Whilst  by  the  method  of  Dumas  the  weight  of  the  amount  of  substance 
is  determined,  which  yields  under  definite  circumstances  a known  volume 
of  vapor,  by  Gay-Lussac’s  method  is  determined  the  volume  of  vapor 
yielded  under  definite  circumstances  by  a previously  weighed  amount  of 
substance.  The  original  process  has  been  judiciously  modified  by  H. 
Schiff.*  The  apparatus  is  excessively  simple,  but  can  only  be  employed 
for  temperatures  under  200°, — it  is  especially  suited  for  temperatures 
under  100°. 

The  cylinder  a (fig.  98),  which  is  destined  to  measure  the  volume  of 

the  vapor,  is  30 — 35  cm.  high  and 
about  2 cm.  wide  ; it  is  provided 
with  a millimetre  scale,  extending 
to  the  open  end ; a table  which  must 
previously  be  drawn  up,  shows  the 
c.  c.  corresponding  to  the  marks  (p. 
19).  The  outer  cylinder  b is  about 
40  cm.  high,  and  broad  in  propor- 
tion. The  height  of  the  latter  in  the 
inside  must  be  accurately  known  in 
mm.  The  handle  c,  which  is  filled 
with  lead,  embraces  the  closed  end 
of  the  measuring  tube  by  means  of 
four  springs.  The  weight  of  this 
handle  must  suffice  to  depress  the 
tube  when  filled  with  vapor,  and 
must  therefore  be  about  130  grm., 
if  the  above  dimensions  are  strictly 
adhered  to.  The  handle  bears  a 
lateral  hook,  on  which  the  thermo- 
meter is  hung. 

A layer  of  mercury,  about  1 5 mm. 
high,  is  first  put  into  the  outer 
cylinder  b.  The  measuring  cylinder 
is  perfectly  filled  with  mercury,  and 
inverted  in  a shallow  mercurial 
trough.  A weighed  quantity  of  the 
fluid  to  be  vaporized  in  a bulb  of 
thin  glass  (fig.  99)  is  now  placed 
underneath  the  opening  of  the  mea- 
suring cylinder,  and  allowed  to  as- 
cend ; the  cylinder  a is  then  transported  to  5,  with  the  aid  of  a 
long-handled  iron  spoon,  of  the  same  form  as  is  in  general  use 
for  combustions  in  oxygen. 

The  bursting  of  the  bulb  and  the  formation  of  vapor  are 
next  brought  about  by  filling  the  outer  cylinder  b cautiously 
Fig.  99.  and  up  to  the  top  with  a hot  fluid.  According  to  the  boiling 
point  of  the  substance  we  use  for  this  purpose  either  boiling 
water,  or  some  saline  solution,  preferably  dilute  glycerine  or  a solution 
of  chloride  of  calcium  in  dilute  glycerine.  The  specific  gravity  of  the 
hot  fluid  is  to  be  determined  in  a suitable  manner  (according  to  H.  Schiff, 


Fig.  98. 


Zeitschrift  f.  analyt.  Chem.  1,  320. 


ORGANIC  ANALYSIS. 


457 


§ 192.] 

by  means  of  an  areometer).  The  outer  cylinder  stands  on  a strong 
low  tripod  in  a small  glass  trough ; the  latter  serves  to  receive  the  fluid, 
which  is  ejected  by  the  vapor  as  it  forms  ; it  is,  moreover,  filled  nearly  up 
to  the  level  of  the  mercury  in  the  outer  cylinder  with  the  hot  fluid,  in 
order  that  the  mercury  may  be  raised  to  the  same  temperature.  After  a 
few  minutes  the  rate  of  cooling  will  have  become  so  much  slower  that  the 
volume  of  the  vapor  may  be  considered  stationary.  Finally,  the  pres- 
sure and  temperature  are  noted,  also  the  height  of  the  mercury  in  the 
measuring  tube,  and  in  the  outer  cylinder  (the  latter  being  read  off  on  the 
scale  of  the  measuring  tube). 

C.  The  determination  of  the  vapor  densities  of  bodies  of  high  boiling 
points  is  made  after  the  method  of  Deville  and  Troost,*  for  a description 
of  which  I must  refer  the  reader  to  the  original  memoir. 

§ 192. 

3.  A great  many  indifferent  organic  bodies  absolutely  refuse  to  combine 
with  bases  or  acids  ; or  only  form  with  them  compounds,  from  which  the 
equivalent  of  the  organic  body  cannot  well  be  determined.  The  equiva- 
lent of  such  substance  is  determined  by  producing  by  the  action  of  acids, 
bases,  halogens,  <fcc.,  upon  the  body  under  examination,  new  compounds 
of  known  or  ascertainable  equivalents.  Or,  lastly,  the  equivalent  is  in- 
ferred from  the  manner  in  which  the  compound  in  question  has  been 
formed.  In  cases  of  this  description,  that  equivalent  is  assumed  to  be  the 
correct  one  which  permits  the  most  simple  explanation  of  the  processes 
of  formation  and  decomposition. 

This  mode  of  determining  the  equivalent  of  substances  is  intimately 
connected  with  the  higher  branches  of  organic  chemistry,  and  cannot  be 
considered  in  detail  here,  as  it  is  impossible  to  give  universally  appli- 
cable methods. 


* Compt.  Rend.  49,  239;  Annal.  d.  Chem.  u.  Pharm.  113,  42. 


DIVISION  II. 


CALCULATION  OF  ANALYSES. 

The  calculation  of  the  results  obtained  by  an  analysis  presupposes, 
as  an  indispensable  preliminary,  a knowledge  of  the  general  laws  of  the 
combining  proportions  of  bodies,  on  the  one  hand,  and  of  the  more  sim- 
ple rules  of  arithmetic  on  the  other.  It  is  a great  error  to  suppose  that 
the  ability  to  make  chemical  calculations  involves  an  extensive  acquain- 
tance with  mathematics,  a knowledge  of  decimal  fractions  and  simple 
equations  being  for  the  most  part  sufficient.  These  remarks  are  not  in- 
tended to  dissuade  students  of  chemistry  from  pursuing  the  highly  im- 
portant study  of  mathematics ; but  merely  to  encourage  those  who  have 
had  no  opportunity  of  entering  more  deeply  into  this  science,  and  who, 
as  experience  has  shown  me,  are  often  afraid  to  venture  upon  chemical 
calculations.  For  this  reason,  I have  made  the  whole  of  the  calculations 
given  in  the  following  paragraphs,  in  the  most  intelligible  manner  pos- 
sible, and  without  logarithms. 

I.  Calculation  of  the  Constituent  sought  from  the  Compound  obtained 
in  the  Analytical  Process , and  exhibition  of  the  Pesult  in  Per-cents. 

§ 193- 

The  bodies  the  weight  of  which  it  is  intended  to  determine,  are  sepa- 
rated, as  we  have  seen  in  Division  I.,  treating  of  the  £<  Execution  of 
Analysis,”  either  in  the  free  state,  or — and  this  most  frequently — in  com- 
binations of  known  composition.  The  results  are  usually  calculated 
upon  100  parts  of  the  examined  substance,  since  this  gives  a clearer  and 
more  intelligible  view  of  the  composition.  In  cases  where  the  several 
constituents  have  been  separated  in  the  free  state,  the  calculation  may 
be  made  at  once ; but  if  the  constituents  have  been  separated  in  com- 
bination with  other  substances,  they  must  first  be  calculated  from  the 
compounds  obtained. 

1.  Calculation  of  the  Pesults  into  Per-cents  by  Weight , in  Cases 
where  the  Substance  sought  has  been  separated  in  the  Free  State. 

a.  Solid  Podies , Liquids , and  Gases , which  have  been  deter- 
mined by  Weight. 

§ 194- 

The  calculation  here  is  exceedingly  simple. 

Suppose  you  have  analyzed  subchloride  of  mercury,  and  separated  the 
mercury  in  the  metallic  state  (§  118,  1).  2*945  grm.  subchloride  of  mer- 

cury have  given  say  2*499  grm.  metallic  mercury. 


§ 195] 


CALCULATION  OF  ANALYSES. 


459 


2*945  : 2-499  ::  100  : a; 

x = 84-85, 

which  means  that  your  analysis  shows  100  parts  of  subchloride  of  mer- 
cury to  contain  84*85  of  mercury,  and  consequently  15*15  of  chlorine. 

Now  as  the  subchloride  of  mercury  is  known  to  consist  of  2 eq.  mer- 
cury and  1 eq.  chlorine,  and  as  the  equivalent  numbers  of  both  these 
elements  are  also  known,  the  true  percentage  composition  of  the  body 
may  be  readily  calculated  from  these  data.  When  analyzing  substances 
of  known  composition  for  practice,  the  results  theoretically  calculated 
and  those  obtained  by  the  analysis  are  usually  placed  in  juxtaposition,  as 
this  enables  the  student  at  once  to  perceive  the  degree  of  accuracy  with 
which  the  analysis  has  been  performed. 


Thus  for  instance — 

Found. 

Calculated  (compare  § 84,  b). 

Mercury.  . . 

,...84-85.... 

84-94 

Chlorine . . . 

...15-15.... 

15-06 

100-00 

100-00 

b.  Gases  which  have  been  determined  by  Measure . 

§ 195. 

If  a gas  has  been  determined  by  measure,  it  is,  of  course,  necessary 
first  to  ascertain  the  weight  corresponding  to  the  volume  found,  before 
the  percentage  by  weight  can  be  calculated. 

But  as  the  exact  weights  of  a definite  volume  of  the  various  gases  have 
been  severally  determined  by  accurate  experiments,  this  calculation  also 
is  a simple  rule-of- three  question,  if  the  gas  may  be  measured  under  the 
same  circumstances  to  which  the  known  relation  of  weight  to  volume  re- 
fers. The  circumstances  to  be  taken  into  consideration  here,  are : 

Temperature  and  Atmospheric  Pressure . 

Besides  these,  the 

Tension  of  the  Aqueous  Vapor 

may  also  claim  consideration  in  cases  where  water  is  used  as  the  confin- 
ing fluid,  'or  generally  where  the  gas  has  been  measured  in  the  moist 
state. 

The  respective  weights  assigned  in  Table  V.*  to  1 litre  of  the  gases 
there  enumerated,  refer  to  a temperature  of  0°,  and  an  atmospheric  pres- 
sure of  0*76  metre  of  mercury.  We  have,  therefore,  in  the  first  place, 
to  consider  the  manner  in  which  volumes  of  gas  measured  at  another 
temperature  and  another  height  of  the  barometer,  are  to  be  reduced  to 
0°  and  0*76  of  the  barometer. 

a.  Reduction  of  a Volume  of  Gas  of  any  given  Temperature  to  0°, 
or  any  other  Temperature  between  0°  and  100°. 

The  following  propositions  regarding  the  expansion  of  gases  were  for- 
merly universally  adopted : — 

1.  All  gases  expand  alike  for  an  equal  increase  of  temperature. 

2.  The  expansion  of  one  and  the  same  gas  for  each  degree  of  the  ther- 
mometer is  independent  of  its  original  density. 


* See  Tables  at  the  end  of  the  volume. 


460 


CALCULATION  OF  ANALYSES. 


[§  195. 


Although  the  correctness  of  these  propositions  has  not  been  fully- 
confirmed  by  the  minute  investigations  of  Magnus  and  Regnault,  yet 
they  may  be  safely  followed  in  reductions  of  the  temperature  of  those 
gases  which  are  most  frequently  measured  in  the  course  of  analytical 
processes,  as  the  coefficients  of  expansion  of  these  gases  scarcely  differ 
from  each  other,  and  as  there  is  never  any  very  considerable  differ- 
ence in  the  atmospheric  pressure  under  which  the  gases  are  severally 
measured. 

The  investigations  just  alluded  to  have  given 

0*3665 

as  the  coefficient  of  the  expansion  of  gases  which  comes  nearest  to  the 
truth ; in  other  words,  as  the  extent  to  which  gases  expand  when 
heated  from  the  freezing  to  the  boiling  point  of  water.  They  expand, 
therefore,  for  every  degree  of  the  centigrade  thermometer, 

p-3665_Q>QQ36 

100 

If  we  wish  to  ascertain  how  much  space  1 c.  c.  of  gas  at  0°  will  occupy 
at  10°,  we  find 

1 X [1  + (10  X 0-003665)]  = 1*03665. 

If  we  wish  to  ascertain  how  much  space  100  c.  c.  at  0°  will  occupy 
at  10°,  we  find 

100  x[l  + (10x0-003665)] 

= 100x  1*03665-103-665. 


If  we  wish  to  know  how  much  space  1 c.  c.  at  10°  will  occupy  at  0°, 
we  find 

1 =0-965. 

1 + (10x0-003665) 

How  much  space  do  103*665  c.  c.  at  10°  occupy  at  0°? 


103-665 

1 + (10x0-003665) 


= 100. 


The  general  rule  of  these  calculations  may  be  expressed  as  follows  : — 
To  calculate  the  volume  of  a gas  from  a lower  to  a higher  temper- 
ature, we  have  in  the  first  place  to  find  the  expansion  for  the  volume 
unit,  which  is  done  by  adding  to  1 the  product  of  the  multiplication  of 
the  thermometrical  difference  by  0*003665  ; and  then  to  multiply  this 
by  the  number  of  volume  units  found  in  the  analytical  process.  On  the 
other  hand,  to  reduce  the  volume  of  a gas  from  a higher  to  a lower  tem- 
perature, we  have  to  divide  the  number  of  volume  units  found  in  the 
analytical  process,  by  1 -f-  the  product  of  the  multiplication  of  the  ther- 
mometrical difference  by  0*003665. 


/3.  Reduction  of  the  Volume  of  a Gas  of  a certain  given  Density  to 
•7  6 Metre  Rarometric  Pressure , or  any  other  given  Pressure. 

According  to  the  law  of  Mariotte,  the  volume  of  a gas  is  inversely 
as  the  pressure  to  which  it  is  exposed ; in  accordance  with  this,  a gas 
occupies  the  greater  space  the  less  the  pressure  upon  it,  and  the  less 
space  the  greater  the  pressure  upon  it. 

Thus,  supposing  a gas  to  occupy  a space  of  10  c.  c.  at  a pressure  of 


§ 195.]  CALCULATION  OF  ANALYSES.  461 

1 atmosphere,  it  will  occupy  1 c.  c.  at  a pressure  of  10  atmospheres, 
and  100  c.  c.  at  a pressure  of  atmosphere. 

Nothing,  therefore,  can  he  more  easy  than  the  reduction  of  a gas  of 
a certain  given  tension  to  760  mm.  bar.  pressure,  or  any  other  given 
pressure,  e.g .,  1000  mm.,  which  is  frequently  used  in  the  analysis  of 
gases. 

Supposing  a gas  to  occupy  100  c.  c.  at  780  mm.  bar.,  how  much 
space  will  it  occupy  at  7 60  mm.  ? 

760  : 780::  100  : x 
x — 102*63. 

How  much  space  will  100  c.  c.  at  750  mm.  bar.  occupy  at  760  mm.  ? 
760  : 750::  100  : x 
a;=98*68. 

How  much  space  will  150  c.  c.  at  760  mm.  bar.  occupy  at  1000  mm.  ? 
1000  : 760::  150  : x 
a?=114. 

y.  Reduction  of  the  Volume  of  a Gas  saturated  with  Aqueous  Vapor , 
to  its  actual  Volume  in  the  Dry  State. 

It  is  a well-known  fact  that  water  has  a tendency,  at  all  temper- 
atures, to  assume  the  gaseous  state.  The  degree  of  this  tendency  (the  ten- 
sion of  the  aqueous  vapor) — which  is  dependent  solely  and  exclusively  up- 
on the  temperature,  and  not  upon  the  circumstance  of  the  water  being  in 
vacuo  or  in  any  gaseous  atmosphere — is  usually  expressed  by  the  height 
of  a column  of  mercury  counterbalancing  it.  The  following  table  indi- 
cates the  amount  of  tension  for  the  various  temperatures  at  which  an- 
alyses are  likely  to  be  made.* 


TABLE. 


Temperature 
(in  degrees  C.) 

Tension  of  the 
aqueous  vapor 
expressed  in 
millimetres. 

Temperature 
(in  degrees  C.) 

Tension  of  the 
aqueous  vapor 
expressed  in 
millimetres. 

0 

4*525 

21 

18-505 

1 

4-867 

22 

19-675 

2 

5*231 

23 

20-909 

3 

5*619 

24 

22*211 

4 

6*032 

25 

23*582 

5 

6-471 

26 

25-026 

6 

6-939 

27 

26-547 

7 

7-436 

28 

28-148 

8 

7-964 

29 

29-832 

9 

8-525 

30 

31*602 

10 

9*126 

31 

33*464 

11 

9*751 

32 

35*419 

12 

10-421 

33 

37*473 

13 

11*130 

34 

39-630 

14 

11-882 

35 

41-893 

15 

12-677 

36 

44-268 

16 

13-519 

37 

46-758 

17 

14-409 

38 

49-368 

18 

15*351 

39 

52*103 

19 

16*345 

40 

54-969 

20 

17*396 

* Compare  Magnus,  Pogg.  Annal.  61,  247. 


462 


CALCULATION  OF  ANALYSES. 


[§  196. 


Therefore,  if  a gas  is  confined  over  water,  its  volume  is,  cceteris paribus, 
always  greater  than  if  it  were  confined  over  mercury ; since  a quantity  of 
aqueous  vapor,  proportional  to  the  temperature  of  the  water,  mixes  with 
the  gas,  and  the  tension  of  this  partly  counterbalances  the  column  of  air 
that  presses  upon  the  gas,  and  to  that  extent  neutralizes  the  pressure. 
To  ascertain  the  actual  pressure  upon  the  gas,  we  must  therefore  sub- 
tract from  the  apparent  pressure  so  much  as  is  neutralized  by  the  ten- 
sion of  the  aqueous  vapor. 

Suppose  we  had  found  a gas  to  measure  100  c.  c.  at  759  mm.  bar., 
the  temperature  of  the  confining  water  being  15°  ; how  much  space 
would  this  volume  of  gas  occupy  in  the  dry  state  and  at  760  mm.  of  the 
barometer  ? 

Our  table  gives  the  tension  of  aqueous  vapor  at  15°  = 12*677 ; the  gas 
is  consequently  not  under  the  apparent  pressure  of  759  mm.,  but  under 
the  actual  pressure  of  759  — 12*677  = 746  323  mm. 

The  calculation  is  now  very  simple ; it  proceeds  in  the  manner  shown 
in  ]6 ; we  say, 

760  : 746*323::  100  : cc 
a = 98*20. 

"When  the  volume  of  a gas  has  thus  been  adjusted  by  the  calculations 
in  a and  /3,  or  y,  to  the  thermometrical  and  barometrical  conditions  to 
which  the  data  of  Table  Y.  refer,  the  percentage  by  weight  may  now  be 
readily  calculated  by  substituting  the  weight  for  the  volume,  and  pro- 
ceeding by  simple  rule  of  three. 

What  is  the  percentage  by  weight  of  nitrogen  in  an  analyzed  sub- 
stance, of  which  0*5  grm.  have  yielded  30  c.  c.  of  dry  nitrogen  gas  at 
0°,  and  7 60  mm.  bar.  ? 

In  Table  Y.  we  find  that  1 litre  (1000  c.  c.)  of  nitrogen  gas  at  0°,  and 
760  mm.  bar.,  weighs  1*25456  grm. 

We  say  accordingly : 

1000:  1-25456::  30:  a? 

x = 0*0376. 


And  then : 


0*5  : 0*0376::  ioo  : cc 
a:  = 7*52. 


The  analyzed  substance  contains  consequently  7*52  per  cent,  by 
weight  of  nitrogen. 

2.  Calculation  of  the  Results  into  Per-cents  by  Weight,  in  Cases 
where  the  Rody  sought  has  been  separated  in  Combination , or  where  a 
Compound  has  to  be  determined  f rom  one  of  its  Constituents. 

§ 196. 

If  the  body  to  be  determined  has  not  been  weighed  or  measured  in 
its  own  form,  but  in  some  other  form,  e.g .,  carbonic  acid  as  carbonate 
of  lime,  sulphur  as  sulphate  of  baryta,  ammonia  as  nitrogen,  chlorine  by 
a standard  solution  of  iodine,  &c.,  its  quantity  must  first  be  reckoned 
from  that  of  the  compound  found  before  the  calculation  described  in  1 
can  be  made. 

This  may  be  accomplished  either  by  rule  of  three  or  by  some  abridged 
method. 

Suppose  we  have  weighed  hydrogen  in  the  form  of  water,  and  have 
found  1 grm.  of  water ; how  much  hydrogen  does  this  contain  ? 


463 


g 196.]  CALCULATION  OF  ANALYSES. 

An  equivalent  of  water  consists  of : 

1 of  hydrogen 

8 of  oxygen 

9 water. 

We  say  accordingly  : 

9 : 1 ::  1 : a; 

07=0*11111. 

From  the  above  proportion  results  the  following  equation : 

1 - 

9x1=*, 

or  0-11111  xl=x. 

Or,  expressed  in  general  terms : 

Water  X 0*11111  — Hydrogen. 

Example. — 

517  of  water;  how  much  hydrogen? 

517x0-11111=57-444. 

The  following  equation  results  also  from  the  above  proportion : 

9 1 

I = x 
1 

9 = 5 

1 

•••  * = 9 

Or,  expressed  in  general  terms, 

Water  divided  by  9 = Hydrogen. 

Example. — 

517  of  water,  how  much  hydrogen  ? 

517 

—g-=57-444. 

In  this  manner  we  may  find  for  every  compound  constant  numbers  by 
which  to  multiply  or  divide  the  weight  of  the  compound,  in  order  to 
find  the  weight  of  the  constituent  sought  (comp.  Table  III.*). 

Thus,  for  instance,  the  nitrogen  may  be  obtained  from  the  double 
bichloride  of  platinum  and  chloride  of  ammonium,  by  dividing  the 
weight  of  the  latter  by  15*96,  or  multiplying  it  by  0*06269 ; thus  the 
carbon  may  be  calculated  from  the  carbonic  acid  by  multiplying  the 
weight  of  the  latter  by  0*2727,  or  dividing  it  by  3*666. 

These  numbers  are  by  no  means  so  simple,  convenient,  and  easy  to 
remember  as  in  the  case  of  hydrogen.  It  is  therefore  advisable,  in  the 
case  of  carbonic  acid,  for  instance,  to  fix  upon  another  general  expres- 
sion, viz., 

Carbonic  acid  X 3 _ fin^nryt  . 

— ar  on, 


* See  Tables  at  the  end  of  the  volume. 


464 


CALCULATION  OF  ANALYSES. 


[§  197. 


which  is  derived  from  the  proportion 

22  : 6 : : the  carbonic  acid  found  : x. 

The  object  in  view  may  also  be  attained  in  a very  simple  manner,  by 
reference  to  table  I V.,*  which  gives  the  amount  of  the  constituent  sought 
for  every  number  of  the  compound  found,  from  1 to  9 ; the  operator 
need,  therefore,  simply  add  the  several  values  together. 

As  regards  hydrogen,  for  instance,  we  find  : — 


TABLE. 


Found. 

Sought. 

1 

2 

3 

4 

5 

6 

7 

8 j 9 

water 

hydrogen 

cmm 

0-22222 

0-33333 

0-44444 

0-55555  | 

0-66667 

0-77778 

0-88889,  j 1-00000 

From  this  table  it  is  seen  that  1 part  of  water  contains  0T1111  of  hy- 
drogen, that  5 parts  of  water  contain  0*55555  of  hydrogen ; 9 parts, 
1*00000,  &c. 

Now  if  we  wish  to  know,  for  instance,  how  much  hydrogen  is  con- 
tained in  5*17  parts  of  water,  we  find  this  by  adding  the  values  for  5 
parts,  for  part,  and  for  T-^-¥  parts,  thus  : — 

0*55555 

0*011111 

0*0077778 

0*5744388 

Why  the  numbers  are  to  be  placed  in  this  manner,  and  not  as  fol- 
lows : — 

0*55555 

0*11111 

0*77778 

1*44444 

is  self-evident,  since  arranging  them  in  the  latter  way  would  be  adding 
the  value  for  5,  for  1,  and  for  7 (5  + 1 -f  7 = 13)  and  not  for  5*17. 
This  reflection  shows  also  that,  to  find  the  amount  of  hydrogen  contained 
in  517  parts  of  water,  the  points  must  be  transposed  as  follows  : — 

55*555 

1*1111 

0*77778 

57*44388 

3.  Calculation  of  the  Hesults  of  Indirect  Analyses  into  Per-  Cents 
by  Weight. 

§ 197. 

The  import  of  the  term  “ indirect  analysis ,”  as  defined  in  § 151,  p.  337, 
shows  sufficiently  that  no  universally  applicable  rules  can  be  laid  down 
for  the  calculations  which  have  to  be  made  in  indirect  analyses.  The 
selection  of  the  right  way  must  be  left  in  every  special  case  to  the  intelli- 
gence of  the  analyst.  I will  here  give  the  mode  of  calculating  the  re- 


* See  Tables  at  the  end  of  the  volume. 


197.] 


CALCULATION  OF  ANALYSES. 


465 


suits  in  the  more  important  indirect  separations  described  in  Section  V. 
They  may  serve  as  examples  for  other  similar  calculations. 

a.  Indirect  Determination  of  Soda  and  Potassa. 

This  is  effected  by  determining  the  sum  total  of  the  chlorides,  and  the 
chlorine  contained  in  them. 

The  calculation  may  be  made  as  follows : 

Suppose  we  have  found  3 grm.  of  chloride  of  sodium  and  chloride  of 
potassium,  and  in  these  3 grm.  T6888  of  chlorine. 

Eq.  Chlorine.  Eq.  K Cl.  Chlorine  found. 

35-46  : 74-57  1*6888  : sc 

x = 3-5514. 

If  all  the  chlorine  present  were  combined  with  potassium,  the  weight 
of  the  chloride  would  amount  to  3-5514.  As  the  chloride  weighs  less, 
chloride  of  sodium  is  present,  and  this  in  a quantity  proportional  to  the 
difference  (i.e.,  3*5514 — 3=0*5514),  which  is  calculated  as  follows  : — 

The  difference  between  the  equivalent  of  K Cl  and  that  of  Na  Cl 
(16*11)  is  to  the  equivalent  of  Na  Cl  (58*46),  as  the  difference  found  is 
to  the  chloride  of  sodium  present : — 

16-11  : 58-46::  0-5514  : x 
x=2  Na  Cl 
and  3-2=1  K Cl. 

From  this  the  following  short  rule  is  derived  : — 

Multiply  the  quantity  of  chlorine  in  the  mixture  by  2*1029,  deduct 
from  the  product  the  sum  of  the  chlorides,  and  multiply  the  remainder 
by  3*6288 ; the  product  expresses  the  quantity  of  chloride  of  sodium 
contained  in  the  mixed  chloride. 

The  calculation  may  also  be  made  by  help  of  the  subjoined  formulae 
(Collier*). 

W=weight  of  mixed  chlorides 
C=  “ ee  chlorine. 

Na  Cl=  Cx  7-6311)- (Wx  3-6288) 

K C1=(W x 4-6288) -(Cx 7-6311) 

Na  0=(C  X 4-0466) -(Wx  1-9243) 

K 0=(W  X 2-9243)  - (C  x 4*8210). 

b.  Indirect  Determination  of  Strontia  and  lime. 

This  may  be  effected  by  determining  the  sum  total  of  the  carbonates, 
and  the  carbonic  acid  contained  in  them  (§  154,  7).  Suppose  we  have 
found  2 grm.  of  mixed  carbonate,  and  in  these  2 grm.  0*7383  of  carbonic 
acid. 

Eq.  C 02  Eq.  SrO,  C 02  C 02  found. 

22  : 73-75  ::  0-7383  : x 

x = 2-47498. 

If,  therefore,  the  whole  of  the  carbonic  acid  were  combined  with 
strontia,  the  weight  of  the  carbonate  would  amount  to  2*47498  grm. 
The  deficiency ,=0*47498  is  proportional  to  the  carbonate  of  lime  pre- 
sent, which  is  calculated  as  follows  : — 

The  difference  between  the  equivalent  of  Sr  O,  C 02 , and  the  equiva- 


* Am.  Jour.  Sci.,  March,  1864,  p.  346. 

30 


466 


CALCULATION  OF  ANALYSES. 


lent  of  Ca  O,  C 02  (23*75)  is  to  the  equivalent  of  Ca  O,  C 02  (50),  as 
the  difference  found  is  to  the  carbonate  of  lime  contained  in  the  mixed 
salt : — 

23*75  : 50::  0*47498  : a; 

The  mixture,  therefore,  consists  of  1 grm.  carbonate  of  lime  and  1 
grm.  carbonate  of  strontia. 

From  this  the  following  short  rule  is  derived  : — 

Multiply  the  carbonic  acid  found  by  3*3523,  deduct  from  the  product 
the  sum  of  the  carbonates,  and  multiply  the  difference  by  2*10526  ; the 
product  expresses  the  quantity  of  the  carbonate  of  lime. 

c.  Indirect  Determination  of  Chlorine  and  Dromine  (§  169,  1). 

Let  us  suppose  the  mixture  of  chloride  and  bromide  of  silver  to  have 
weighed  2 grm.,  and  the  diminution  of  weight  consequent  upon  the 
transmission  of  chlorine  to  have  amounted  to  0*1  grm.  How  much 
chlorine  is  there  in  the  mixed  salt,  and  how  much  bromine  ? 

The  decrease  of  weight  here  is  simply  the  difference  between  the 
weight  of  the  bromide  of  silver  originally  present,  and  that  of  the  chlo- 
ride of  silver  which  has  replaced  it  ; if  this  is  borne  in  mind,  it  is  easy 
to  understand  the  calculation  which  follows  : — 

The  difference  between  the  equivalents  of  bromide  of  silver  and  chlo- 
ride of  silver  is  to  the  equivalent  of  bromide  of  silver  as  the  ascertained 
decrease  of  weight  is  to  x,  i.e .,  to  the  bromide  of  silver  originally  pres- 
ent in  the  mixture  : — 

44*54  : 187*97::  0*1  : x 
a?=0*422025. 

The  2 grm.  of  the  mixture  therefore  contained  0*422025  grm.  bromide 
of  silver,  and  consequently  2 — 0*422025=1*577975  grm.  chloride  of 
silver. 

It  results  from  the  above,  that  we  need  simply  multiply  the  ascer- 
tained decrease  of  weight  by 

l87-9Zt,e.,  by  4-22025 
44-54 

to  find  the  amount  of  bromide  of  silver  originally  present  in  the  ana- 
lyzed mixture.  And  if  we  know  this,  we  also  know  of  course  the 
amount  of  the  chloride  of  silver ; and  from  these  data  we  deduce  the 
quantities  of  chlorine  and  bromine,  as  directed  in  § 196,  and  the  per- 
centages as  directed  in  § 193. 

Supplement  to  I. 

REMARKS  ON  LOSS  AND  EXCESS  IN  ANALYSES,  AND  ON  TAKING  THE 

AVERAGE. 

§ 198. 

if,  in  the  analysis  of  a substance,  one  of  the  constituents  is  estimated 
from  the  loss,  or,  in  other  words,  by  subtracting  from  the  original 
weight  of  the  analyzed  substance  the  ascertained  united  weight  of  the 
other  constituents,  it  is  evident  that  in  the  subsequent  percentage  calcu- 
lation the  sum  total  must  invariably  be  1QQ.  Every  loss  suffered  or 


CALCULATION  OF  ANALYSES. 


467 


§ 198.1 


excess  obtained  in  the  determination  of  the  several  constituents  will, 
of  course,  fall  exclusively  upon  the  one  constituent  which  is  estimated 
from  the  loss.  Hence  estimations  of  this  kind  cannot  be  considered 
accurate,  unless  the  other  constituents  have  been  determined  by  good 
methods,  and  with  the  greatest  care.  The  accuracy  of  the  results  will, 
of  course,  be  the  greater,  the  less  the  number  of  constituents  determined 
in  the  direct  way. 

if,  on  the  other  hand,  every  constituent  of  the  analyzed  compound 
has  been  determined  separately,  it  is  obvious  that,  were  the  results  ab- 
solutely accurate,  the  united  weight  of  the  several  constituents  must  be 
exactly  equal  to  the  original  weight  of  the  analyzed  substance.  Since, 
however,  as  we  have  seen  in  § 96,  certain  inaccuracies  attach  to  every 
analysis,  without  exception,  the  sum  total  of  the  results  in  the  percen- 
tage calculation  will  sometimes  exceed,  and  sometimes  fall  short  of, 
100. 

In  all  cases  of  this  description,  the  only  proper  way  is  to  give  the 
results  as  actually  found. 

Thus,  for  instance,  Pelouze  found,  in  his  analysis  of  chromate  of 
chloride  of  potassium, 


Potassium 

21*88 

Chlorine 

19*41 

Chromic  acid 

58*21 

99*50 

Berzelius,  in  his  analysis  of  sesquioxide  of  uranium  and  potassa, 

Potassa  12*8 

Sesquioxide  of  uranium  86*8 


99*6 

Plattner,  in  his  analysis  of  pyrrhotine, 

Of  Fahlun.  Of  Brasil. 

Iron  59*72  59*64 

Sulphur  40*22  40*43 


99*94  100*07 

It  is  altogether  inadmissible  to  distribute  any  chance  deficiency  or  ex- 
cess proportionately  among  the  several  constituents  of  the  analyzed  com- 
pound, as  such  deficiency  or  excess  of  course  never  arises  from  the 
several  estimations  in  the  same  measure  ; moreover,  such  “ doctoring  ” 
of  the  analysis  deprives  other  chemists  of  the  power  of  judging  of  its 
accuracy.  No  one  need  be  ashamed  to  confess  having  obtained  some- 
what too  little  or  somewhat  too  much  in  an  analysis,  provided,  of  course, 
the  deficiency  or  excess  be  confined  within  certain  limits,  which  differ 
in  different  analyses,  and  which  the  experienced  chemist  always  knows 
how  to  fix  properly. 

In  cases  where  an  analysis  has  been  made  twice,  or  several  times,  it 
is  usual  to  take  the  mean  as  the  most  correct  result.  It  is  obvious  that 
an  average  of  the  kind  deserves  the  greater  confidence  the  less  the  re- 
sults of  the  several  analyses  differ.  The  results  of  the  several  analyses 
must,  however,  also  be  given,  or,  at  all  events,  the  maximum,  and 
minimum. 


468 


CALCULATION  OF  ANALYSES. 


[§  199. 

Since  the  accuracy  of  an  analysis  is  not  dependent  upon  the  quantity 
of  substance  employed  (provided  always  this  quantity  be  not  altogether 
too  small),  the  average  of  the  results  of  several  analyses  is  to  be  taken 
quite  independently  of  the  quantities  used ; in  other  words,  you  must 
not  add  together  the  quantities  used,  on  the  one  hand,  and  the  weights 
obtained  in  the  several  analyses  on  the  other,  and  deduce  from  these 
data  the  percentage  amount ; but  you  must  calculate  the  latter  from 
the  results  of  each  analysis  separately,  and  then  take  the  mean  of  the 
numbers  so  obtained. 

Suppose  a substance,  which  we  will  call  AB,  contains  fifty  per  cent, 
of  A ; and  suppose  two  analyses  of  this  substance  have  given  the  follow- 
ing results : 

(1)  2 grm.  AB  gave  0*99  grm.  of  A. 

(2)  50  “ “ 24*00  “ 

From  1,  it  results  that  AB  contains  49*50  per  cent,  of  A. 

“ 2,  “ “ 48*00  “ 


Total 97*50 

Mean 48*75 

It  would  be  quite  erroneous  to  say 

2 + 50  = 52  of  AB  gave  0*99  + 24*00  = 24*99  of  A, 
therefore  100  of  AB  contain  48*06  of  A; 

for  it  will  be  readily  seen  that  this  way  of  calculating  destroys  nearly 
altogether  the  influence  of  the  more  accurate  analysis  (1)  upon  the  aver- 
age, on  account  of  the  proportionally  small  amount  of  substance  used. 

II.  Deduction  of  Empirical  Formulae. 

§ 199. 

If  the  percentage  composition  of  a substance  is  known,  a so-called  em- 
pirical formula  may  be  deduced  from  this  ; in  other  words,  the  relative 
proportion  of  the  several  constituents  may  be  expressed  in  equivalents — 
in  a formula  which,  upon  recalculation  in  per-cents  will  give  numbers 
corresponding  perfectly,  or  nearly,  with  those  obtained  by  the  analysis. 
We  are  compelled  to  confine  ourselves  to  the  expression  of  empirical  for- 
mulae, in  the  case  of  all  substances  of  which  we  cannot  determine  the 
equivalent,  as  e.g.y  woody  fibre,  mixed  substances,  &c. 

The  method  of  deducing  empirical  formulae  is  very  simple,  and  will  be 
readily  understood  from  the  following  reflections  .* — 

How  should  we  proceed  to  find  the  relative  number  of  equivalents  in 
carbonic  acid? 

We  should  say: — 

The  equivalent  of  the  oxygen  is  to  the  amount  of  oxygen  in  the  equi- 
valent of  carbonic  acid,  as  1 is  to  x , i.e.,  to  the  number  of  equivalents  of 
oxygen  contained  in  carbonic  acid ; 

8 : 16 : : 1 : x 
x=2. 

In  the  same  manner  we  should  find  the  number  of  equivalents  of  car- 
bon by  the  following  proportion  : — 


§ 199-1 


CALCULATION  OF  ANALYSES. 


469 


6 : 6 ::  1 : x 

(equivalent  of  carbon)  (carbon  in  one  equivalent 
of  carbonic  acid) 
x—\. 

Now  let  us  suppose  we  did  not  know  the  equivalent  of  carbonic  acid, 
but  simply  its  percentage  composition,  viz., 

27*273  carbon 
72*727  oxygen 


100*000  carbonic  acid ; 


the  relative  proportion  of  the  equivalents  might  still  be  ascertained,  even 
though  any  other  given  number,  say  100,  be  selected  for  the  equivalent 
of  carbonic  acid.  Let  us  suppose  we  adopt  100  as  the  equivalent  of  car- 
bonic acid ; thus, 

8 : 72*727  ::  1 : x 

(Eq.  O)  (Amount  of  oxygen  in  the 

assumed  eq.  100) 
a*=9*0910 


ind 

6 : 27*273  ::  l:x 

(Eq.  C)  (Amount  of  carbon  in  the 

assumed  eq.  100) 
cc=4*5455. 


We  see  here  that  although  the  numbers  which  express  the  relative 
proportion  of  the  equivalents  of  oxygen  and  carbon  have  changed,  yet 
the  relative  proportion  itself  remains  the  same  ; since 

4*5455  : 9*0910::  1 : 2. 


The  process  may  accordingly  be  expressed  in  general  terms  as  fol- 
lows : 

Assume  any  number,  say  100  (because  this  is  the  most  convenient), 
as  the  equivalent  of  the  compound,  and  ascertain  how  often  the  equiva- 
lent of  each  constituent  severally  is  contained  in  the  amount  of  the  same 
constituent  present  in  100  parts.  When  you  have  thus  found  the  num- 
bers expressing  the  relative  proportion  of  the  equivalents,  you  have 
attained  your  purpose — viz.,  the  deduction  of  an  empirical  formula. 
Still,  it  is  usual  to  reduce  the  numbers  found  to  the  simplest  expres- 
sion. 

Now  let  us  take  a somewhat  complicated  case,  e.g .,  the  deduction  of 
the  empirical  formula  for  mannite. 

The  percentage  composition  of  mannite  is 

39*56  of  carbon 
7*69  of  hydrogen 
52*75  of  oxygen 

100*00 

This  gives  the  following  proportions  : 


6 : 

: 39*56: 

::  1 

: x 

a?— 6*593 

1 : 

: 7*69: 

: 1 

: x 

#=7*690 

8 : 

: 52*75: 

::  1 

: x 

#=6*593 

470 


CALCULATION  OF  ANALYSES. 


[§  1W. 


We  have  now  the  empirical  formula  for  mannite,  viz., 

Qj-693  Hrego  06.59l3 

A glance  shows  that  the  number  of  the  equivalents  of  the  carbon  is 
equal  to  that  of  the  equivalents  of  the  oxygen  ; and  the  question  is  now 
whether  the  relative  proportion  found  may  not  be  expressed  by  smaller 
numbers. 

A simple  calculation  suffices  to  answer  this  question,  viz., 

6*593  : 7*690::  60  : a? 

(Any  other  number  might  be  substituted  for  60,  as  the  third  term  of 
the  proportion,  but  60  is  very  suitable,  since  it  is  divisible  without  re- 
mainder by  most  of  the  numbers.) 

x=70 

We  have  accordingly  now  the  simple  formula, 

C60  H70  o60=c6  Ht  06. 

The  percentage  composition  of  mannite  given  above  having  been  cal- 
culated from  the  formula,  of  course  the  latter  is  evolved  again  without 
ambiguity.  Now  let  us  take  the  results  of  an  actual  analysis. 

Oppermann  obtained,  upon  the  combustion  of  T593  grm.  mannite, 
with  oxide  of  copper,  2*296  carbonic  acid  and  1*106  water.  This  gives 
in  per-cents, 

39*31  carbon 
7*71  hydrogen 
52*98  oxygen 


100*00 

which,  calculated  as  above,  gives 

^6-552  H77t0  06.q22 

as  the  first  expression  of  the  empirical  formula ; and  by  the  propor- 
tion: 

6*552  : 7*710=6  : a* 
x::  7*06 

A glance  at  these  numbers  shows  that  7*06  may  be  properly  ex- 
changed for  7,  and  also  that  the  difference  between  6*552  and  6*622  is 
so  trifling  that  both  may  be  expressed  by  the  same  number.  These 
considerations  lead  therefore  likewise  to  the  formula 

c6  h7  o6 

The  proof  whether  the  formula  is  correct  or  not  is  obtained  by  its  re- 
calculation in  per-cents.  The  less  the  calculated  percentage  differs  from 
that  found,  the  more  reason  there  is  to  believe  in  the  correctness  of 
the  formula.  If  the  difference  is  more  considerable  than  can  be  account- 
ed for  by  the.  defects  inherent  in  the  methods,  there  is  every  reason  to 
believe  the  formula  fallacious,  in  which  case  it  is  necessary  to  establish 
a more  correct  one ; for  it  will  be  readily  seen  that,  invthe  case  of  sub- 
stances of  which  the  equivalent  is  not  known,  different  formulae  may  be 
deduced  from  one  and  the  same  analysis,  or  from  several  very  nearly 


200.] 


CALCULATION  OF  ANALYSES. 


471 


corresponding  analyses ; since  the  numbers  found  are  never  absolutely 
correct,  but  only  approximate. 

Thus,  for  instance,  in  the  case  of  mannite  : 


Calculated 

Pound 

for 

for 

C6  39*56 

c8 

39*67 

39*31 

H7  7*69 

H9 

7*44 

7*71 

06  52*75 

o8 

52*89 

52*98 

100*00 

100*00 

100*00 

III.  Deduction 

OF 

Rational 

Formulae. 

200. 


If  both  the  percentage  composition  and  the  equivalent  of  a substance 
are  known,  it  is  easy  to  deduce  its  rational  formula-— that  is,  a formula 
expressing  not  only  the  relative  proportion  of  the  equivalents,  but  also 
their  absolute  number. 

The  following  examples  may  serve  for  illustration : — 


1.  Deduction  of  the  Dational  Formula  of  Hyposulphuric  Acid. 


Analysis  has  given,  in  the  first  place,  the  percentage  Composition  of 
hyposulphuric  acid,  and,  in  the  second  place,  the  percentage  composi- 
tion of  liyposulphate  of  potassa,  viz., 


Sulphur 

Oxygen 


. 44*44  Potassa  . . . 

. 55*56  Hyposulphuric  acid 


Hyposulphuric  acid  . 100.00  Hyposulphate  of  potassa 

(Equivalent  of  potassa=47*ll) 

How : 

39*551  : 60*449  : : 47*11  : a?  :r=72 


39*551 

60*449 


100*000 


Hence  72  is  the  sum  of  the  equivalents  of  the  constituents  contained 
in  hyposulphuric  acid — in  other  terms,  the  equivalent  of  hyposulphuric 
acid. 

Having  thus  ascertained  the  correct  equivalent  of  hyposulphuric  acid, 
it  is  unnecessary  to  assume  a hypothetical  one,  as  we  are  obliged  to  do 
in  the  case  of  mannite. 

Thus  we  may  state  at  once  : 

100  : 44*44::  72  : a?  a;=32; 
i.e.— the  sum  of  the  equivalents  of  the  sulphur ; and  again : 

100  : 55*56::  72  : x cc=40; 
i.e.=  the  sum  of  the  equivalents  of  the  oxygen. 

How  the  equivalent  of  sulphur,  i.e.  16,  is  contained  twice  in  32  ; and 
the  equivalent  of  oxygen,  i.e.  8,  is  contained  five  times  in  40  ; the  ra- 
tional formula  for  hyposulphuric  acid  is  accordingly, 


06. 

2.  Deduction  of  the  Dational  Formula  of  Denzoic  Acid. 

Stenhouse  obtained  from  0*3807  hydrated  benzoic  acid,  dried  at  100°3 
0*9575  carbonic  acid  and  0*1698  water. 


472  CALCULATION  OF  ANALYSES.  [§  200. 

0*4287  benzoate  of  silver,  dried  at  100°,  gave  0*202  silver.  From 
these  numbers  result  the  following  percentage  compositions : — 

Carbon 68*67  Oxide  of  silver  . . . 50*67 

Hydrogen  ....  4*95  Benzoic  acid  ....  49*33 

Oxygen 26*38  

Benzoate  of  silver  . . 100*00 

Hydrated  benzoic  acid  100*00 

(Equivalent  of  the  oxide  of  silver=115*97) 

50*67  : 49*33  : : 115*97  : * ®=112*904 

i.e.  the  equivalent  of  anhydrous  benzoic  acid  ; that  of  the  hydrated  acid 
accordingly=112*904-|- 9=121*904  • we  say  therefore  now 

100  : 68*67  : : 121*904  : x sb=83-711 
100:  4*95::  121*904:®  ®=  6*035 

100  : 26*38  : : 121*904  : ® ®=32*158 

6 is  contained  in  83*711  13*95  times 

1 “ 6*035  6*03  “ 

8 “ 32*158  4*02  “ 

A glance  at  these  quotients  suffices  to  show  that  13*95  may  be  ex- 
changed for  14,  6*03  for  6,  and  4*02  for  4.  The  rational  formula  for 
the  hydrate  of  benzoic  acid  is  accordingly, 

C'4  h6  o4. 

This  gives,  by  calculation,  The  numbers  found  were, 


C 68*85 

68*67 

H 4*92 

4*95 

O 26*23 

26*38 

100*00 

100*00 

3.  Deduction  of  the  Rational  Formula  of  Theine. 

Stenhouse’s  analysis  of  theine,  free  from  water  of  crystallization, 
gave  the  following  results  : — 

1.  0.285  grm.  substance  gave  0*5125  carbonic  acid  and  0*132  water. 

2.  Combustion  with  oxide  of  copper  gave  a mixture  of  C02  and  N,  in 
the  proportion  of  4 of  the  former  to  1 of  the  latter. 

3.  0*5828  grm.  of  the  double  salt  of  hydrochlorate  of  theine  and  bi- 
chloride of  platinum,  gave  0*143  platinum. 

From  these  numbers  results  the  following  percentage  composition : — 


Carbon  . 

. 49*05 

Hydrogen 

. 5*14 

Nitrogen  . 

. 28*61 

Oxygen  . 

. 17*20 

100*00 

and  196*91  as  the  equivalent  of  theine.  For  there  is  every  reason  to 
suppose  that  the  composition  of  the  double  salt  of  hydrochlorate  of 
theine  and  bichloride  of  platinum  is 

Theine  + H Cl  + Pt  CL* 


CALCULATION  OF  ANALYSES. 


473 


§ 200.1 

The  equivalent  of  this  double  salt  is  found  by  the  following  propor- 
tion : 

0*143  : 0*5828  : : 98*94  (eq.  platinum) : a*  a=403*23  ; 

and  consequently  the  equivalent  of  theine,  by  subtracting  from  403*23 
the  sum  of  1 eq.  bichloride  of  platinum  (169*86)  and  1 eq.  hydrochloric 
acid  (36*46) 

403*23-(169*86  x 36*46)=196*91. 

This  supplies  the  following  proportions  : — 


100 

: 49*05 : 

: 196*91  : x 

#=96*584 

100 

: 5*14: 

: 196*91  : x 

a?=  10*121 

100 

: 28*61: 

: 196*91  : x 

a?=56*336 

100 

: 17*20: 

: 196*91  : x 

cc=33*868 

6 

is  contained  in  96*584, 

16*09  times 

1 

a 

10*121, 

10*12  “ 

14 

(( 

56*336, 

4*02  “ 

8 

a 

33*868, 

4*23  “ 

for  which  numbers  may  be  substituted,  16,  10,  4,  and  4,  respectively, 
and  we  get  the  following  formula : 

C16  Hl0  N4  04 

Found 
49*05 
5*14 


This  gives  by  calculation, 
C 49*47 
H 5*15 


N 28*89 
O 16*49 


28*61 

17*20 


100*00  100*00 

The  double  hydrochlorate  of  theine  and  bichloride  of  platinum  gives 
platinum  in  100  parts, 

Calculated.  Found. 

24*70  24*53 

4.  Special  Method  of  Deducing  Rational  Formulce  for  Oxygen  Salts. 

a.  In  the  case  of  Compounds  containing  no  Isomorphous  Constituents. 

The  rational  formulae  for  oxygen  salts  may  be  deduced  also  by  a me- 
thod different  from  the  foregoing,  viz.,  by  ascertaining  the  ratio  which 
the  respective  quantities  of  oxygen  bear  to  each  other.  This  method  is 
exceedingly  simple. 

In  an  analysis  of  crystallized  sulphate  of  soda  and  ammonia,  I found, 

Soda  ....  17*93 

Oxide  of  ammonium  . 15*23 

Sulphuric  acid  . . 46*00 

Water  . . 20*84 


100*00 


31  of  NaO  contain  8 of  O,  consequently  17*93  of  NaO  contain  4*63  of  O. 
26  . . NH40  ..  8..0,  ..  15*23..  NH40  ..  4*68 ..  O. 

40..SO3  ..  24..  O,  ..  46*00..  S03  ..  27*60..  O. 

9..  HO  ..  8 . . O,  ..  20*84..  HO  ..  18*52..  O. 


474 


CALCULATION  OF  ANALYSES. 


[§  200. 


Now 

4-63  : 4-68  : 27-60  : 18*52  = 1 : 1*01  : 5-97  : 4-00  = 1 : 1 : 6 : 4, 
and  this  leads  to  the  formula 


Na  O,  N H4  O,  2 S 03  x 4 H O 
or,  Na  O,  S 03+N  H,  O,  S 03-f  4 aq. 

b.  In  the  case  of  Compounds  containing  Isomorphous  Constituents. 

It  is  a well-known  fact  that  isomorphous  constituents  may  replace 
each  other  in  all  proportions;  therefore,  in  establishing  a formula  for 
compounds  containing  isomorphous  constituents,  the  latter  are  taken 
collectively  / that  is,  they  are  expressed  in  the  formula  as  one  and  the 
same  body.  This  very  frequently  occurs  in  the  calculation  of  formulae 
for  minerals. 

A.  Erdmann  found  in  monradite 


Silicic  acid 

56-17 

Amount  of  Oxygen. 

29-957 

Magnesia 

31-63  . 12.652  ) 

- . 14.601 

Protoxide  of  iron 

8-56  . 1-949  j 

Water 

4-04 

3-590 

100-40 


Now 


3-59  : 14-601  : 29-957=1  : 4-07  : 8-3=1  : 4 : 8. 


Designating  1 eq.  metal  by  It,  we  obtain  from  these  numbers  the  for- 
mula:— 

4 (R.O,  Si  Oa)  + HO  or  4 j.  O,  Si  O,  ) +aq. 


Not  only  isomorphous  substances,  but  generally  all  bodies  of  analo- 
gous composition  possess  the  faculty  of  replacing  each  other  in  com- 
pounds ; thus  we  find  that  KO,  Na  O,  Ca  O,  Mg  O,  &c.,  replace  each 
other.  These  substances  likewise  must  be  expressed  collectively  in  the 
formula. 

Abich  found  in  andesine 

Amount  of  Oxygen. 


Silicic  acid 

59-60 

9 m 

31-79 

Alumina 

Sesquioxide  of  iron 
Lime 

24-28 

1-58 

5-77 

. 11-22) 

0- 48 

1- 61" 

11-70 

Magnesia 

Soda 

1-08 

6-53 

0- 43 

1- 68 

> • 

3-90 

Potassa 

1-08 

0-18* 

99-92 

Now 


3-90  : 11-70  : 31*79=1  : 3 : 8-15=1  : 3 : 8. 


Designating  1 eq.  metal  by  It,  we  obtain  from  these  numbers  the 
formula : — 


It  O -j-  It  3 Ojj-f-4  Si  02 
=K  O,  Si  02  +Ra  03,  3 Si  Oa, 


475 


§ 201.]  CALCULATION  OF  ANALYSES. 

which  may  likewise  be  written  : — 

Ca  ] 

|4o,Si02  +£»  [ 0„  3 Si  0,. 

Showing  thus  that  this  mineral  is  leucite  (K  Oj  Si  02  + Al2  03, 3 Si  03 ), 
in  which  the  greater  part  of  the  potassa  is  replaced  by  lime,  soda,  and 
magnesia,  and  a portion  of  the  alumina  by  sesquioxide  of  iron. 

These  remarks  respecting  the  deduction  of  formulae  for  oxygen  salts, 
aPPly  course  equally  to  metallic  sulphides. 


IY.  Calculation  of  the  Density  of  the  Vapors  of  Volatile 
Bodies,  and  Application  of  the  Results,  as  a Means  of  con- 
trolling their  Analyses,  and  determining  their  Equiva- 
lents. 

§ 201. 

The  specific  gravity  of  a compound  gas  is  equal  to  the  sum  of  the 
specific  gravities  of  its  constituents  in  one  volume. 

E.g.,  2 volumes  of  hydrogen  gas  and  1 volume  of  oxygen  gas  give  2 
volumes  of  aqueous  vapor.  If  they  gave  simply  1 volume  of  aqueous 
vapor,  the  specific  gravity  of  the  latter  would  be  equal  to  the  sum  total 
of  the  specific  gravity  of  the  oxygen  and  double  the  specific  gravity  of 
the  hydrogen — viz., 

2x0-0093=0*1386 
-f  1*1083 
=1*24(59 


But  as  they  give  2 volumes  of  aqueous  vapor,  this  1*2469  is  distri- 
buted between  the  two  volumes ; accordingly  the  specific  gravity  of  the 
vapor  is 


1*2469 

9 


=0*62345 


It  will  be  readily  seen  that  the  knowledge  of  the  density  of  the  vapor 
of  a compound  supplies  an  excellent  means  of  controlling  the  correctness 
of  the  relative  proportions  of  the  equivalents  assumed  in  a formula. 

For  instance : from  the  results  of  the  ultimate  analysis  of  camphor, 
has  been  deduced  the  empirical  formula : 

cI0  h8  o. 

Dumas  found  the  density  of  the  vapor  of  camphor =5  *3 12.  Now,  by 
what  means  do  we  find  whether  this  formula  is  correct  with  respect  to  the 
relative  proportions  of  the  equivalents  ? 

Specific  gravity  of  the  vapor  of  carbon  0*831 

u (i  hydrogen  gas  0*0693 

ie  u oxygen  gas  1*108 

10  eq.  C = 10  volumes=10x 0*831  =8*310 
8 eq.  H =;  1 6 volumes^  16  x 0*0693  = 1*109 
1 eq.  0=  1 volume  = 1x1*1081  = 1*108 


10*527 


476 


CALCULATION  OF  ANALYSES. 


This  sum  is  almost  exactly  twice  as  large  as  the  specific  gravity  found 
by  direct  experiment  (^|^=5‘263) ; which  shows  that  the  relative  pro- 
portions of  the  equivalents  are  correctly  given  in  the  empirical  formula 
of  camphor.  But  whether  the  formula  is  correct,  also,  with  regard  to 
the  absolute  number  of  equivalents,  cannot  be  determined  simply  from 
the  density  of  the  vapor,  because  we  do  not  know  to  how  many  volumes 
of  camphor  vapor  1 equivalent  of  camphor  corresponds.  Liebig  assumes 
the  equivalent  of  camphor  to  correspond  to  2 volumes,  and  gives  accord- 
ingly the  formula  C10  H8  O ; whilst  Dumas  assumes  it  to  correspond  to 
4 volumes,  and  accordingly  gives  the  formula  C20  H16  02. 

The  knowledge  of  the  density  of  the  vapor  affords,  therefore,  in  reality, 
simply  a means  of  controlling  the  correctness  of  the  analysis,  but  not  of 
establishing  a rational  formula ; and  although  it  is  made  to  serve  some- 
times for  the  latter  purpose,  yet  this  can  be  done  only  in  the  case  of  sub- 
stances for  which  we  are  able  to  infer  from  analogy  a certain  ratio  of 
condensation  : thus,  for  instance,  experience  proves  that  1 equivalent  of 
the  hydrates  of  the  volatile  organic  acids,  of  alcohols,  &c.,  corresponds 
to  4 volumes. 

In  § 200,  2,  we  have  found  the  rational  formula  of  hydrated  benzoic 
acid  to  be  C14  H6  04.  Dumas  and  Mitscherlich  found  the  vapor  den- 
sity to  be  4*26. 

Now  nearly  the  same  number  is  obtained  by  dividing  by  4 the  sum 
total  of  the  gravities  of  the  several  constituents  contained  in  1 equiva- 
lent of  hydrated  benzoic  acid,  viz. , 

14  volumes  C = 1 1*634 
12  volumes  H=  0*831 
4 volumes  0=  4*432 


16*897 

= 4*224 

4 

Hermann  Kopp*  has  called  attention  to  the  fact  that,  if  the  equivalent 
of  a substance  refers  to  H = 1,  and  the  vapor  density  of  the  same  to  at- 
mospheric air  = 1,  the  division  of  the  equivalent  by  the  vapor  density 
gives  the  following  quotients, 

28*88  14*44  7*22 

according  as  the  formula  corresponds  to  4,  2,  or  1 volume  of  vapor : 
28*88  corresponds  to  a condensation  to  4 volumes 
14-44  “ “ “ 2 “ 

7-22  u t(  “1  volume 

Kopp  calls  these  numbers  normal  quotients.  If  the  vapor  density  is 
not  quite  exact,  but  only  approximate  (determined  by  experiment), 
other  numbers  are  found,  but,  to  be  correct,  these  must  come  near  the 
normal  numbers. 

If,  therefore,  we  know  the  equivalent  of  a body,  we  may,  with  the 
greatest  facility,  ascertain  whether  the  determination  of  the  vapor 
density  of  the  body  has  given  approximately  correct  results  or  not. 

Gay-Lussac  found  the  vapor  density  of  alcohol  to  be  1*6133  ; 
Dalton,  2*l.f 

* Compt.  rend.  44,  1347  ; Chem.  Centralbl.  1857,  595. 
f Gmelin’s  Handbook,  viii.,  199. 


§ 201.] 


CALCULATION  OF  ANALYSES. 


477 


Now,  which  is  the  correct  number  ? 

The  equivalent  of  alcohol,  C4  H6  02,  is  46. 

— =21-9 

2-1 


1-6133 

It  is  evident  that  Gay-Lussac’s  number  is  approximately  correct, 
for  the  quotient  found  by  it  comes  very  near  the  normal  quotient, 
28-88. 

Again,  if  we  know  the  equivalent  of  a body,  and  the  number  of 
volumes  of  vapor  corresponding  to  1 equivalent,  we  may  also,  with  the 
same  facility,  calculate  the  theoretical  vapor  density  of  the  body.  For 
instance,  the  equivalent  of  hydrated  benzoic  acid  is  122.  The  division 
of  this  number  by  28*88  gives  4*224  as  vapor  density,  which  is  the 
same  as  that  found  by  actual  experiment. 

And,  lastly,  if  we  know  approximately  (i.e.  by  experiment)  the 
vapor  density  of  a body,  and  also  the  ratio  of  condensation,  we  may, 
with  the  aid  of  these  quotients,  approximately  calculate  the  equivalent 
of  the  body. 

E.g.  The  vapor  density  of  acetic  ether  has  been  found  = 3*112. 
The  multiplication  of  this  number  by  28*88  gives  89*87  as  the 
equivalent  of  acetic  ether,  which  comes  near  the  actual  equivalent, 
88. 

Having  thus  shown  how  the  knowledge  of  the  vapor  density  of  a 
body  is  turned  to  account  as  a means  of  controlling  the  results  of  an 
ultimate  analysis  of  the  same,  we  will  now  proceed  to  show  how  the 
vapor  density  is  calculated  from  the  data  obtained  as  described  in  § 191, 
A and  B. 

A.  We  will  take  as  an  illustration  Dumas’  estimation  of  the  specific 
gravity  of  the  vapor  of  camphor. 

The  results  of  the  process  were  as  follows : — 

Temperature  of  the  air  .......  13*5° 

Barometer  . . . . . . . . .742  mm. 

Temperature  of  the  bath  at  the  moment  of  sealing  the  globe  244° 
Increase  of  the  weight  of  the  globe  ....  . 0*708  grm. 

Volume  of  mercury  entering  the  globe  ....  295  c.c.  * 

Residual  air  .........  0 

Now,  to  find  the  vapor  density,  we  have  to  determine, 

1.  The  weight  of  the  air  which  the  globe  holds  (as  a necessary  step  to 
the  determination  of  2). 

2.  The  weight  of  the  camphor  vapor  which  the  globe  holds. 

3.  The  volume  to  which  the  camphor  vapor  corresponds,  at  0°  and 
760  mm. 

The  solution  of  these  questions  is  quite  simple ; and  if  the  calcula- 
tion, notwithstanding,  appears  somewhat  complicated,  this  is  merely 
owing  to  certain  reductions  and  corrections  which  are  required. 

1.  The  weight  of  the  air  in  the  globe. 

The  globe  holds  295  c.  c.,  as  we  see  by  the  volume  of  mercury  ic- 
quired  to  fill  it. 


478 


CALCULATION  OF  ANALYSES. 


First,  what  is  the  volume  of  295  c.  c.  of  air  at  13*5°  and  742  mm. 
at  0°  and  760  mm.  ? 

The  question  is  solved  according  to  the  directions  of  8 195  as 
follows:— 


760  : 742::  295  : a 

ic=288  c.  c. 


and  again : 


288 


288 


(At  13*5°  and  760  mm.) 


= 274  c.  c.  (at  0°  and  760  mm.) 


1 + (13-5x0-00366)  1-04941 

ir  at  0°  and 
ngly 

0-00129366  x 274=0-35446  grm. 


Now  1 c.  c.  of  air  at  0°  and  760  mm.  weighs  0*00129366  grm. ; 274 
c.  c.  weigh  accordingly 


2.  The  Weight  of  the  Vapor. 

At  the  beginning  of  the  experiment  we  tared  the  globe -f  the  air 
within  it;  we  afterwards  weighed  the  globe-}- the  vapor  (but  without 
the  air) ; — to  find,  therefore,  the  actual  weight  of  the  vapor,  it  is  not 
sufficient  to  subtract  the  tare  from  the  weight  of  the  globe  filled  with 
vapor,  since  [glass  4-  vapor) — (glass  air)  is  not = vapor  ; but  we  have 
either  to  subtract,  in  the  first  place,  the  weight  of  the  air  from  the  tare, 
or  to  add  the  weight  of  the  air  to  the  increase  of  the  weight  of  the 
globe.  Let  us  do  the  latter : — 


Weight  of  air  in  the  globe 
Increase  of  weight  of  globe 


= 0*35446  grm. 
=0*70800  grm. 


The  weight  of  the  vapor  is  accordingly  =1*06246  grm. 

3.  The  Volume  to  which  this  Weight  of  1*06246  grm.  of  Vapor  cor- 
responds at  0°  and  760  mm. 

"We  know  from  the  above-given  data  that  this  weight  corresponds  to 
295  c.  c.  at  244°,  and  742  mm.  Before  we  can  proceed  to  reduce  this 
volume  according  to  the  directions  of  § 195,  the  following  corrections 
are  necessary : — 

a.  244°  of  the  mercurial  thermometer  correspond,  according  to  the 
experiments  of  Magnus,  to  239°  of  the  air  thermometer  (see  Table 
VI.). 

b.  According  to  Dulong  and  Petit,  glass  expands  (commencing  at 

0°)  v°lume  for  each  degree  C.  The  volume  of  the  globe  at 

the  moment  of  sealing  was  accordingly — 


295  + ?^l-  = 297  c.  c. 

35000 

If  we  now  proceed  to  reduce  this  volume  to  0°  and  760  mm.  we  find 
by  the  proportion, 

760  : 742 :: 297  : x 

x (i.e.,  c.  c.  of  vapor  at  760  mm.  and  239°)=290; 
and  by  the  equation. 


201.] 


CALCULATION  OF  ANALYSES. 


479 


1 + (239x0*00366) 

x ( i.e . c.  c.  of  vapor  at  760  mm.  and  0°)  = 154*6. 

154*6  c.  c.  of  camphor  vapor  at  0°  and  760  mm.,  weigh  accordingly 
1*06246  grm. 

1 litre  (1000  c.  c.)  weighs  consequently  6*87231  grm.;  since 

154*6  : 1*06246::  1000  : 6*87231. 

Now  1 litre  of  air  at  0°  and  760  mm.  weighs  1*29366  grm. 

The  specific  gravity  of  the  camphor  vapor  consequently  = 5*312  ; since 

1*29366  : 6*87231 ::  1 : 5*312. 

B.  We  will  here  take  an  imaginary  determination  of  the  vapor  density 
of  ether  as  our  example. 

Bulb  + ether  =0*3445  grm. 

“ empty  =0*2040  grm. 

Weight  of  ether  =0*1405  grm. 

Temperature  of  the  glycerine  solution  in  the  outer  cylinder  100° 

Sp.  gr.  of  the  same  solution  at  100° 1 

Barometer 752  mm. 

Difference  between  the  height  of  the  mercury  in  the  outer  ) 

and  inner  cylinders j 50  mm. 

Height  of  the  column  of  mercury  in  the  outer  cylinder.  . 60  mm. 

Inside  height  of  the  outer  cylinder 400  mm. 

Volume  of  the  vapor  as  found  from  the  tube’s  table.  ...  60  c.  c. 

The  glycerine  solution  being  400  — 60=  340  mm.  high  and  having 
a specific  gravity  of  1,  corresponds  to  a column  of  mercury  of  25  mm. 
The  vapor  consequently  is  under  the  pressure  of  752-1-25  — 50  = 727  mm. 
60  c.  c.  of  ether  vapor  at  100°  and  727  mm.  consequently  weigh  0*1405. 
We  have  now  to  calculate  the  weight  of  60  c.  c.  of  air  under  the  same 
circumstances. 

1000  c.  c.’air  of  0°  and  760  mm.  weigh  1*29366  grm.  Heated  to  100° 
they  become  1366*5  c.  c.  (comp.  § 195,  a),  and  with  the  pressure  reduced 
to  727  mm.  th&se  expand  again  to  1428*5  c.  c.  (comp.  § 195,  3).  But 
the  air  still  weighs  the  same,  viz.,  1*29366  grm.  .*.  1428*5  c.  c.  weighing 
1*29366,  60  c.  c.  weigh,  under  the  same  circumstances,  0*05433  grm. ; 

0-1  40'5 

hence  the  sp.  gr.  of  ether  vapor  = - = 2*586 

1 6 * 0*05433 


PAST  II. 


SPECIAL  PART. 


31 


1.  ANALYSIS  OF  FLESH  WATER  (SPRING-WATER, 
RIVER- WATER,  &c.)* 


§ 202. 

The  analysis  of  the  several  kinds  of  fresh  water  is  usually  restricted  to 
the  quantitative  estimation  of  the  following  substances  : — 

a.  Bases:  Soda,  lime,  magnesia. 

b.  Acids  : Sulphuric  acid,  nitric  acid,  silicic  acid,  carbonic  acid,  chlorine. 

c.  Mechanically  suspended  Matters  : Clay,  &c. 

We  confine  ourselves,  therefore,  here  to  the  estimation  of  these  bodies. 

I.  The  Water  is  clear. 

1.  Determination  of  the  Chlorine. — This  may  be  effected,  either,  a,  in 
the  gravimetric,  or,  b , in  the  volumetric  way. 

a.  Gravimetrically. 

Take  500 — 1000  grin,  or  c.  c.f  Acidify  with  nitric  acid,  ahd  precipi- 
tate with  nitrate  of  silver.  Filter  when  the  precipitate  has  completely 
subsided  (§  141,  I.,  a).  If  the  quantity  of  the  chlorine  is  so  inconsider- 
able that  the  solution  of  nitrate  of  silver  produces  only  a slight  turbidity, 
evaporate  a larger  portion  of  the  water  to  -J-,  -J,  &c.,  of  its  bulk,  filter, 

wash  the  precipitate,  and  treat  the  filtrate  as  directed. 

b.  Volumetrically. 

Evaporate  1000  grm.  or  c.  c.  to  a small  bulk,  and  determine  the 
chlorine  in  the  residual  fluid,  without  previous  filtration,  by  solution  of 
nitrate  of  silver,  with  addition  of  chromate  of  potassa  (§  141,  I.,  b.  a). 

2.  Determination  of  the  Sulphuric  Acid. — Take  1000  grm.  or  c.  c. 
Acidify  with  hydrochloric  acid  and  mix  with  chloride  of  barium.  Filter 
after  the  precipitate  has  completely  subsided  (§  132,  I.,  1).  If  the  quan- 
tity of  the  sulphuric  acid  is  very  inconsiderable,  evaporate  the  acidified 
water  to  J,  -jt,  &c.,  of  the  bulk,  before  adding  the  chloride  of  barium. 

3.  Determination  of  Nitric  Acid. — If,  on  testing  the  residue  on  eva- 
poration of  a water  for  nitric  acid,  such  a strong  reaction  is  obtained 
that  the  presence  of  a determinable  quantity  of  the  acid  may  be  inferred, 
evaporate  1000  or  2000  c.  c.  of  the  water  in  a porcelain  dish,  wash  the 
residue  into  a flask  (if  any  carbonate  of  lime,  &c.,  remains  sticking  to 
the  dish,  it  may  be  disregarded,  as  all  nitrates  are  soluble),  evaporate  in 
the  flask  still  further,  if  necessary,  and  in  the  small  quantity  of  residual 
fluid  determine  the  nitric  acid  according  to  § 149,  d , a,  or  /?.  The  for- 
mer method  is  less  suitable  if  the  residue  on  evaporation  contains 
organic  matter.  If  the  latter  method  is  employed,  the  evaporated  water 

* Compare  Qualitative  Analysis,  p.  262,  et  seq.  See  a paper  recently  read 
before  the  Chemical  Society  by  Dr.  Miller — the  Society’s  Journal  (2),  iii. , 117, 
et  seq.  ; also,  Frankland,  idem  (2).  iv.,  239,  and  vi. , 77;  and  Wanklyn,  Chap- 
man, and  Smith,  idem  vi. , 152. 

f As  the  specific  gravity  of  fresh  water  differs  but  little  from  that  of  pure  water, 
the  several  quantities  of  water  may  safely  be  measured  instead  of  weighed.  The 
calculation  is  facilitated  by  taking  a round  number  of  c.  c. 


SPECIAL  PART. 


484 


[§  202. 


must  first  be  beated  with  potash  solution  till  no  more  alkaline  vapors 
escape. 

4.  Determination  of  the  Silicic  Acid , Lime,  and  Magnesia. 

Evaporate  1000  grm.  or  c.  c.  to  dryness — after  addition  of  some  hydro- 
chloric acid — preferably  in  a platinum  dish,  treat  the  residue  with 
hydrochloric  acid  and  water,  filter  off  the  separated  silicic  acid,  and  treat 
the  latter  as  directed  § 140  II.,  a.  Estimate  the  lime  and  magnesia  in 
the  filtrate  as  directed  § 154,  6,  a (29). 

5.  Determination  of  the  total  Residue  and  of  the  Soda. 

a.  Evaporate  1000  grm.  or  c.  c.  of  the  water,  with  proper  care,  to 
dryness  in  a weighed  platinum  dish,  first  over  a lamp,  finally  on  the 
water-bath.  Expose  the  residue,  in  the  air-bath,  to  a temperature  of 
about  180°,  until  no  further  diminution  of  weight  takes  place.  This 
gives  the  total  amount  of  the  salts. 

b.  Treat  the  residue  with  water,  and  add,  cautiously,  pure  dilute  sul- 
phuric acid  in  moderate  excess ; cover  the  vessel  during  this  operation 
with  a dish,  to  avoid  loss  from  spirting ; then  place  on  the  water-bath, 
without  removing  the  cover.  After  ten  minutes,  rinse  the  cover  by  means 
of  a washing  bottle,  evaporate  the  contents  of  the  dish  to  dryness,  expel 
the  free  sulphuric  acid,  ignite  the  residue,  in  the  last  stage  with  addition 
of  some  carbonate  of  ammonia  (§  97,  1),  and  weigh.  The  residue  con- 
sists of  sulphate  of  soda,  sulphate  of  lime,  sulphate  of  magnesia,  and 
some  separated  silicic  acid.  It  must  not  redden  moist  litmus  paper.  The 
quantity  of  the  sulphate  of  soda  in  the  residue  is  now  found  by  subtract- 
ing from  the  weight  of  the  latter  the  known  weight  of  the  silicic  acid  and 
the  weight  of  the  sulphate  of  lime  and  sulphate  of  magnesia  calculated 
from  the  quantities  of  these  earths  found  in  4. 

6.  Direct  Estimation  of  the  Soda. 

The  soda  may  also  be  determined  in  the  direct  way,  with  comparative 
expedition,  by  the  following  method  : — 

Evaporate  1250  grm.  or  c.  c.  of  the  water,  in  a dish,  to  about  a,  and 
then  add  2 — 3 c.  c.  of  thin  pure  milk  of  lime,  so  as  to  impart  a strongly 
alkaline  reaction  to  the  fluid ; heat  for  some  time  longer,  then  wash  the 
contents  of  the  dish  into  a quarter-litre  flask.  (It  is  not  necessary  to  rinse 
every  particle  of  the  precipitate  into  the  flask ; but  the  whole  of  the  fluid 
must  be  transferred  to  it,  and  the  particles  of  the  precipitate  adhering 
to  the  dish  well  washed,  and  the  washings  also  added  to  the  flask.)  Allow 
the  contents  to  cool,  dilute  to  the  mark,  shake,  allow  to  deposit,  filter 
through  a dry  filter,  measure  oft*  200  c.  c.  of  the  filtrate,  corresponding 
to  1000  grm.  of  the  water,  transfer  to  a quarter-litre  flask,  mix  with  car- 
bonate of  ammonia  and  some  oxalate  of  ammonia,  add  water  up  to  the 
mark,  shake,  allow  to  deposit,  filter  through  a dry  filter,  measure  off  200 

c.  c.,  corresponding  to  800  grm.  of  the  water,  add  some  chloride  of  am- 
monium,* evaporate,  ignite,  and  weigh  the  residual  chloride  of  sodium 
as  directed  § 98,  2.f  „ 

_ * 

* To  convert  the  still  remaining  sulphate  of  soda,  on  ignition,  into  chloride  of 
sodium. 

f This  process,  which  entirely  dispenses  with  washing,  presents  one  source  of 
error — viz. , the  space  occupied  by  the  precipitates  is  not  taken  into  account.  The 
error  resulting  from  this  is,  however,  so  trifling,  that  it  may  safely  be  disregarded, 
as  the  excess  of  weight  amounts  to  g^o  at  the  most. 


§ 202.] 


ANALYSIS  OF  FRESH  WATER. 


485 


7.  Calculate  the  numbers  found  in  1 — 6 to  1000  parts  of  water,  and 
determine  from  the  data  obtained  the  amount  of  carbonic  acid  in  com* 
bination,  as  follows  : — 

Add  together  the  quantities  of  sulphuric  acid  corresponding  to  the 
bases  found,  and  subtract  from  the  sum,  first,  the  amount  of  sulphuric 
acid  precipitated  from  the  water  by  chloride  of  barium  (2),  secondly, 
the  amount  corresponding  to  the  nitric  acid  found,  and  thirdly,  the 
amount  corresponding  to  the  chlorine  found  (for  1 eq.  Cl,  1 eq.  S03)  ; 
the  remainder  is  equivalent  to  the  carbonic  acid  combined  with  the 
bases  in  the  form  of  neutral  carbonates.  40  parts  of  sulphuric  acid  re- 
maining after  subtracting  the  quantities  just  stated,  correspond  accord- 
ingly to  22  parts  of  carbonic  acid. 

If,  by  way  of  control,  you  wish  to  determine  the  combined  carbonic 
acid  in  the  direct  way,  evaporate  1000  grin,  or  c.  c.  of  the  water,  in  a 
flask,  to  a small  bulk  ; add  tincture  of  cochineal,  then  standard  nitric 
acid,  and  proceed  as  directed  p. 

8.  Control. 

If  the  quantities  of  the  soda,  lime,  magnesia,  sulphuric  acid,  nitric 
acid,  silicic  acid,  carbonic  acid,  and  chlorine  are  added  together,  and  an 
amount  of  oxygen  corresponding  to  the  chlorine  (since  this  latter  is 
combined  with  metal  and  not  with  oxide)  is  subtracted  from  the  sum, 
the  remainder  must  nearly  correspond  to  the  total  amount  of  the  salts 
found  in  5,  a.  Perfect  correspondence  cannot  be  expected,  since,  1, 
upon  the  evaporation  of  the  water  chloride  of  magnesium  is  partially 
decomposed,  and  converted  into  a basic  salt ; 2,  the  silicic  acid  expels 
some  carbonic  acid ; and  3,  it  being  difficult  to  free  carbonate  of  mag- 
nesia from  water  without  incurring  loss  of  carbonic  acid,  the  residue 
remaining  upon  the  evaporation  of  the  water  contains  the  carbonate  of 
magnesia  as  a basic  salt,  whereas,  in  our  calculation,  we  have  assumed 
the  quantity  of  carbonic  acid  corresponding  to  the  neutral  salt. 

9.  Determination  of  the  free  Carbonic  Acid. 

In  the  case  of  well-water  this  may  be  conveniently  executed  by  the 
process  described  § 139,  j3  (p.  286).  We  here  obtain  the  carbonic  acid 
which  is  contained  in  the  water  over  and  above  the  quantity  corre- 
sponding to  the  monocarbonates,  or  in  other  words,  the  carbonic  acid 
which  is  free  and  which  is  combined  with  the  carbonates  to  bicar- 
bonates. 

10.  Determination  of  the  Organic  Matter. 

Many  well-waters  contain  so  much  organic  matter  as  to  be  quite 
yellow,  others  contain  traces,  and  many  again  may  be  said  to  be  free 
from  such  substances.  The  exact  estimation  of  organic  matter  is  by  no 
means  an  easy  task,  and  the  method  usually  adopted — viz.,  ignition  of 
the  residue  of  the  water  dried  at  180°,  treatment  with  carbonate  of 
ammonia,  gentle  ignition  again,  and  calculation  of  the  organic  matter 
from  the  loss  of  weight — yields  merely  an  approximate  result,  since  we 
can  never  be  sure  as  to  the  condition  of  the  carbonate  of  magnesia  in 
the  residue  dried  at  180°  and  in  the  same  after  ignition,  and  since  the 
silicic  acid  expels  some  carbonic  acid,  which  is  not  taken  up  again  on 
treatment  with  carbonate  of  ammonia,  &c.  However,  it  is  generally  a 
matter  of  importance,  in  regard  to  the  application  of  a water,  to  know 
the  quantity  of  organic  matter  present,  hence  we  have  lately  had  re- 


486 


SPECIAL  PART. 


course  to  the  permanganate  of  potassa,  and  sought  to  determine  the 
organic  matter  at  least  comparatively  from  the  quantity  of  the  oxidizing 
agent  reduced  by  a definite  amount  of  water.  Forchhammer*  heats  a 
certain  quahtity  of  the  water  to  boiling,  runs  in  a dilute  solution  of 
permanganate  from  a burette,  till  a faint  but  permanent  redness  occurs, 
he  then  allows  to  cool,  and  to  a like  quantity  of  pure  distilled  water 
adds  permanganate  from  the  same  burette  till  a similar  coloration  is 
formed ; lastly,  he  finds  from  the  difference  the  quantity  of  permanga- 
nate reduced  by  the  substances  contained  in  the  water.  Em.  MoNNiERf 
uses  a solution  of  1 grm.  permanganate  of  potassa  in  1 litre  of  distilled 
water,  purified  by  rectification  over  some  permanganate  of  potassa.  He 
warms  500  c.  c.  of  the  water  to  70°,  adds  1 c.  c.  pure  sulphuric  acid, 
and  then  the  standard  solution  of  permanganate  to  incipient  coloration, 
and  finally,  deducting  from  the  quantity  employed  the  quantity  neces- 
sary to  impart  the  same  coloration  to  500  c.  c.  of  purified  distilled 
water,  acidulated  and  heated  as  above,  he  obtains  the  quantity  of  per- 
manganate which  has  been  reduced  by  the  substances  present  in  the 
water  tested. 

Comparative  experiments  of  this  kind  are  often  of  value  ; but  they 
do  not  provide  us  with  a numerical  expression  for  the  amount  of  or- 
ganic substances  present,  since  waters  contain  sometimes  other  bodies, 
especially  nitrites,  sulphuretted  hydrogen,  and  salts  of  protoxide  of 
iron,  which  have  the  property  of  reducing  permanganate  of  potassa, 
and  since  again  organic  substances  decompose  various  quantities  of  this 
salt,  according  to  their  nature. 

II.  The  water  is  not  clear. 

Fill  a large  flask  of  known  capacity  with  the  water,  close  with  a glass 
stopper,  and  allow  the  flask  to  stand  in  the  cold  until  the  suspended 
matter  is  deposited ; draw  off  the  clear  water  with  a siphon  as  far  as 
practicable,  filter  the  bottoms,  dry  or  ignite  the  contents  of  the  filter, 
and  weigh.  Treat  the  clear  water  as  directed  in  I. 


Respecting  the  calculation  of  the  analysis,  I remark  simply  that  the 
results  are  usually J arranged  upon  the  following  principles  : — 

The  chlorine  is  combined  with  sodium ; if  there  is  an  excess,  this  is 
combined  with  calcium.  If,  on  the  other  hand,  there  remains  an  ex- 
cess of  soda,  this  is  combined  with  sulphuric  acid.  The  sulphuric  acid , 
or  the  remainder  of  the  sulphuric  acid,  as  the  case  may  be,  is  combined 
with  lime.  The  nitric  acid  is,  as  a rule,  to  be  combined  with  lime. 
The  silicic  acid  is  put  down  in  the  free  state,  the  remainder  of  the  lime 
and  the  magnesia  as  carbonates,  either  neutral  or  acid,  according  to 
circumstances. 

It  must  always  be  borne  in  mind  that  the  results  of  the  qualitative 
analysis  may  render  another  arrangement  of  the  acids  and  bases  neces- 
sary^ For  instance,  if  the  evaporated  water  reacts  strongly  alkaline, 
carbonate  of  soda  is  present,  generally  in  company  with  sulphate  of 
soda  and  chloride  of  sodium,  occasionally  also  with  nitrate  of  soda. 


* Institut.  1849,  383  ; Jahresber.  von  v.  Liebig-  u.  Kopp.  1849,  603. 
f Compt.  rend.  50.  1084  ; Dingler’s  polyt.  Journ.  157,  132. 

% A certain  latitude  is  here  allowed  to  the  analyst’s  discretion. 


ACIDIMETRY. 


487 


§§  203,  204.] 

The  lime  and  magnesia  are  then  to  be  entirely  combined  with  carbonic 
acid. 

In  the  report,  the  quantities  are  represented  in  parts  per  1000  (or 
1000,000),  and  also  in  grains  per  gallon. 


For  technical  purposes,  it  is  sometimes  sufficient  to  estimate  the 
hardness  of  the  water  (the  relative  amount  of  lime  and  magnesia  in  it) 
by  means  of  a standard  solution  of  soap.  A detailed  description  of  this 
method,  which  was  first  employed  by  Clark,  may  be  found  in  Bolley 
& Paul’s  Handbook  of  Technical  Analysis.  See  also  Sutton’s  Volu- 
metric Analysis. 

2.  Acidimetry. 

A.  Estimation  by  Specific  Gravity. 

§ 203. 

Tables,  based  upon  the  results  of  exact  experiments,  have  been  drawn 
up,  expressing  in  numbers  the  relation  between  the  specific  gravity  of 
the  aqueous  solution  of  an  acid,  and  the  amount  of  real  acid  contained 
in  it.  Therefore,  to  know  the  amount  of  real  acid  contained  in  an 
aqueous  solution  of  an  acid,  it  suffices,  in  many  cases,  simply  to  deter- 
mine its  specific  gravity.  Of  course  the  acids  must,  in  that  case,  be 
free,  or  at  least  nearly  free  from  admixtures  of  other  substances  dis- 
solved in  them.  Now,  as  most  common  acids  are  volatile  (sulphuric 
acid,  hydrochloric  acid,  nitric  acid,  acetic  acid),  any  non-volatile  admix- 
ture may  be  readily  detected  by  evaporating  a sample  of  the  acid  in  a 
small  platinum  or  porcelain  dish. 

The  determination  of  the  specific  gravity  is  effected  either  by  com- 
paring the  weight  of  equal  volumes  of  water  and  acid,*  or  by  means  of 
a good  hydrometer.  The  estimations  must,  of  course,  be  made  at  the 
temperature  to  which  the  Tables  refer. 

The  Tables  on  pages  488 — 491  give  the  relations  between  the  spe- 
cific gravity  and  the  strength  for  sulphuric  acid,  hydrochloric  acid, 
nitric  acid,  and  acetic  acid. 

In  all  cases  in  which  the  determination  of  the  specific  gravity  fails  to 
attain  the  end  in  view,  or  which  demand  particular  accuracy,  the  fol- 
lowing method  is  employed. 

B.  Estimation  by  Saturation  with  an  Alkaline  Fluid  of  known 

Strength.! 

§ 204. 

This  method  requires  : — 

A dilute  acid  of  known  strength. 

An  alkaline  fluid  of  known  strength. 

* See  Greville  Williams’  Chemical  Manipulation. 

f According  to  Nicholson  and  Price  (Chem.  Gaz.,  1856,  p.  80)  the  common 
method  of  acidimetry  is  not  suited  for  determining  free  acetic  acid,  on  account 
of  the  alkaline  reaction  of  neutral  acetate  of  soda ; however,  Otto  (Anna!  d. 
Chem.  u.  Pharm  102,  69)  has  clearly  demonstrated  that  the  error  arising  from 
this  is  so  inconsiderable  that  it  may  safely  be  disregarded. 


488 


SPECIAL  PART, 


[§  204. 


TABLE  I. 


Showing  the  percentages  of  hydrated  and  anhydrous  acid  corresponding 
to  various  specific  gravities  of  aqueous  Sulphuric  Acid  by  Bineau  ; 
calculated  for  15°,  by  Otto. 


Specific 

gravity. 

Percentage 
of  hydrated 
acid. 

Percentage 
of  anhydrous 
acid. 

Specific 

gravity. 

Percentage 
of  hydrated 
acid. 

Percentage 
of  anhydrous 
acid. 

1 -8426 

100 

81  -63 

1-398 

50 

40  81 

1-842 

99 

80-81 

1-3886 

49 

40-00 

1 -8406 

98 

80-00 

1-379 

48 

39  18 

1-840 

97 

79-18 

1-370 

47 

38-36 

1 -8384 

96 

78-36 

1-361 

46 

37-55 

1-8376 

95 

77-55 

1-351 

45 

36  73 

1 -8356 

94 

76-73 

1-342 

44 

35-82 

1-834 

93 

75-91 

1-333 

43 

35  10 

1-831 

92 

75-10 

1-324 

42 

34-28 

1-827 

91 

74-28 

1-315 

41 

33-47 

1-822 

90 

73-47 

1.306 

40 

32  65 

1-816 

89 

72-65 

1 -2976 

39 

31-83 

1-809 

88 

71  -83 

1-289 

38 

31-02 

1-802 

87 

7102 

1-281 

37 

30-20 

1-794 

86 

7040 

1-272 

36 

29-38 

1-786 

85 

69-38 

1-264 

35 

28-57 

1-777 

84 

68  57 

1-256 

34 

27-75 

1-767 

83 

67-75 

1-2476 

33 

26-94 

1-756 

82 

66  94 

1-239 

32 

26-12 

1 745 

81 

66-12 

1-231 

31 

25-30 

1-734 

80 

65-30 

1-223 

30 

24-49 

1-722 

79 

64-48 

1 -215 

29 

23-67 

1-710 

78 

63  67 

1 -2066 

28 

22-85 

1-698 

77 

62-85 

1-198 

27 

22  03 

1-686 

76 

62  04 

1-190 

26 

21  -22 

1-675 

75 

61-22 

1-182 

25 

20-40 

1-663 

74 

60-40 

1174 

24 

19-58 

1-651 

73 

59-59 

1-167 

23 

18-77 

1-639 

72 

58-77 

1159 

22 

17-95 

1-627 

71 

57-95 

1 1516 

21 

17-14 

1.615 

70 

57-14 

1-144 

20 

16-32 

1 -604 

69 

56*32 

1-136 

19 

15-51 

1-592 

68 

55-59 

1-129 

18 

14-69 

1-580 

67 

54-69 

1121 

17 

13-87 

1-568 

66 

53-87 

1-1136 

16 

13  06 

1-557 

65 

53-05 

1-106 

15 

12-24 

1-545 

64 

52-24 

1 098 

14 

11-42 

1 534 

63 

51  -42 

1-091 

13 

10-61 

1-523 

62 

50-61 

1-083 

12 

9-79 

1 -512 

61 

49-79 

1 0756 

11 

8-98 

1-501 

60 

48-98 

1068 

10 

8-16 

1-490 

59 

48-16 

1061 

9 

7-34 

1-480 

58 

47-34 

1-0536 

8 

6-53 

1-469 

57 

46.53 

1-0464 

7 

5-71 

1 -4586 

56 

45-71 

1039 

6 

4-89 

1-448 

55 

44-89 

1-032 

5 

4-08 

1-438 

54 

44-07 

1-0256 

4 

3-26 

1428 

53 

43  26 

1019 

3 

2-445 

1-418 

52 

42-45 

1013 

2 

1-63 

1-408 

51 

41-63 

1-0064 

1 

0-816 

§ 204.] 


ACIDIMETRY. 


489 


TABLE  II. 

Showing  the  percentages  of  anhydrous  acid  corresponding  to 
specific  gravities  of  aqueous  Hydrochloric  Acid,  by  Ure. 
rat  ure  15°. 


Specific 

gravity. 

Percentage 
of  hydrochloric 
acid  gas. 

1 2000 

40-777 

1-1982 

40-369 

11964 

39-961 

1-1946 

39-554 

1 -1928 

39*146 

1-1910 

38-738 

1-1893 

38-330 

1-1875 

37-923 

1-1857 

37-516 

1-1846 

3? -108 

1 -1822 

36-700 

1-1802 

36-292 

1-1782 

35-884 

11762 

35-476 

11741 

35-068 

11721 

34-660 

1-1701 

34  252 

11681 

33-845 

11661 

33-437 

1-1641 

33  029 

1-1620 

32-621 

1-1599 

32-213 

1-1578 

31  -805 

1-1557 

31-398 

1-1537 

30  990 

1-1515 

30-582 

1*1494 

30  174 

1*1473 

29-767 

1-1452 

29-359 

1-1431 

28-951 

' 1-1410 

28-544 

1-1389 

28-136 

1-1369 

27-728 

1-1349 

27-321 

1-1328 

26*913 

1*1308 

26-505 

1*1287 

26  098 

1-1267 

25-690 

1*1247 

25-282 

1-1226 

24*874 

1-1206 

24-466 

1-1185 

24  058 

1-1164 

23-650 

1*1143 

23-242 

1*1123 

22-834 

11102 

22-426 

1-1082 

22  019 

1-1061 

21-611 

1 -1041 

21  -203 

1*1020 

20-796 

Specific 

gravity. 

Percentage 
of  hydrochloric 
acid  gas. 

1-1000 

20-388 

1 -0980 

19-980 

1 -0960 

19-572 

1 -0939 

19-165 

10919 

18-757 

1 -0899 

18-349 

1-0879 

17-941 

1 -0859 

17-534 

1 -0838 

17-126 

1-0818 

16-718 

1 -0798 

16-310 

1 -0778 

15-902 

1 -0758 

15*494 

1-0738 

15-087 

1-0718 

14-679 

1 -0697 

14-271 

1 -0677 

13-863 

1 -0657 

13-456 

1-0637 

13  049 

10617 

12-641 

1 0597 

12-233 

1 -0577 

11  -825 

1 -0557 

11-418 

1-0537 

11-010 

10517 

10-602 

1 -0497 

10-194 

1 -0477 

9 786 

1 0457 

9-379 

1 0437 

8-971 

1-0417 

8-563 

1 -0397 

8155 

1*0377 

7-747 

1*0357 

7-340 

1*0337 

6-932 

1 -0318 

6*524 

1 -0298 

6-116 

1 0279 

5-709 

1-0259 

5-301 

1-0239 

4*893 

1-0220 

4-486 

1*0200 

4-078 

1*0180 

3*670 

10160 

3-262 

1*0140 

2-854 

10120 

2-447 

1*0100 

2-039 

1*0080 

1-631 

1*0060 

1-124 

1 -0040 

0-816 

1-0020 

0-408 

various 

Tempe- 


490 


SPECIAL  PART. 


[§  204. 


TABLE  III. 

Showing  the  percentages  of  anhydrous  acid  corresponding  to  various 
specific  gravities  of  aqueous  Nitric  Acid  by  Ure.  Temperature 
15°. 


Specific 

gravity. 

Percentage 
of  anhy- 
drous acid. 

Specific 

gravity. 

Percentage 
of  anhy- 
drous acid. 

Specific 

gravity. 

Percentage 
of  anhy- 
drous acid. 

Specific 

gravity. 

Percentage 
of  anhy- 
drous acid. 

1*500 

79*7 

1*419 

59  8 

1*295 

39*8 

1*140 

19*9 

1*498 

78*9 

1*415 

59*0 

1*289 

39*0 

1*134 

19*1 

1*496 

78*1 

1*411 

58*2 

1 *283 

38*3 

1*129 

18*3 

1*494 

77*3 

1*406 

57*4 

1*276 

37*5 

1*123 

17*5 

1*491 

76*5 

1*402 

56*6 

1 270 

36*7 

1*117 

16*7 

1*488 

75*7 

1*398 

55*8 

1*264 

35*9 

1 111 

15*9 

1 *485 

74*9 

1*394 

55*0 

1 258 

35  T 

1 *105 

15*1 

1*482 

74*1 

1*388 

54*2 

1*252 

34*3 

1*099 

14*3 

1*479 

73*3 

1 *383 

53*4 

1*246 

33*5 

1 *093 

13*5 

1 *476 

72*5 

1*378 

52*6 

1*240 

32*7 

1*088 

12*7 

1*473 

71*7 

1*373 

51  8 

1*234 

31*9 

1*082 

11*9 

1 *470 

70*9 

1 *368 

51*1 

1*228 

31*1 

1*076 

11  *2 

1*467 

70*1 

1*363 

50*2 

1*221 

30*3 

1*071 

10*4 

1*464 

69  3 

1*358 

49*4 

1*215 

29*5 

1*065 

9*6 

1 *460 

68*5 

1*353 

48*6 

1*208 

28*7 

1 *059 

8*8 

1 *457 

67*7 

1*348 

47  9 

1*202 

27*9 

1 054 

8*0 

1*453 

66*9 

1*343 

47*0 

1*196 

27*1 

1*048 

7*2 

1 *450 

66*1 

1*338 

46*2 

1*189 

26*3 

1*043 

6*4 

1*446 

65*3 

1*332 

45*4 

1*183 

25*5 

1*037 

5*6 

1*442 

64*5  ' 

1*327 

44*6 

1*177 

24*7 

1 *032 

4*8 

1*439 

63*8 

1*322 

43*8 

1*171 

23*9 

1*027 

4*0 

1 *435 

63*0 

1*316 

43*0 

1*165 

23*1 

1021 

3*2 

1*431 

62*2 

1*311 

4 2*2 

1*159 

22*3 

1*016 

2*4 

1*427 

61*4 

1*306 

41*4 

1*153 

21*5 

1*011 

1*6 

1*423 

60*6 

1*300 

40*4 

1*146 

20*7 

1*005 

0*8 

a Preparation  of  the  Solutions. 

The  acid  may  be  of  such  strength  as  to  contain  in  1000  c.  c.  the  exact 
equivalent  nnmber  (H=l)  of  grammes  of  the  acid,  accordingly,  40  grm. 
sulphuric  acid,  36*46  hydrochloric  acid,  36  oxalic  acid,  &c.  Acids  of 
this  strength  are  called  normal  acids  j equal  volumes  of  them  have  the 
same  power  of  saturating  alkalies.  Their  use  is  convenient  for  techni- 
cal analyses.  For  nicer  work  we  employ  more  dilute  acids,  either  deci- 
liormal,  or  of  some  other  convenient  standard.  As  the  first  step  in  the 
preparation  of  a dilute  sulphuric  acid,  of  convenient  strength  for  ordi- 
nary use,  dilute  20  cubic  centimetres  of  oil  of  vitriol  with  water  to  the 
volume  of  2 litres. 

The  standard  alkali  is  made  from  commercial  caustic  potash  ; this  is 
dissolved  in  water  and  diluted  until  a given  volume,  e.  g.  5 c.  c.,  neutral- 
izes 4 to  5 c.  c.  of  the  standard  acid,  as  is  determined  by  a few  rough 
trials. 

The  alkali-solution  thus  obtained  is  heated  to  boiling  in  a flask,  and  a 
little  freshly-slaked  lime  is  added  to  decompose  any  carbonate  of  pot- 
ash. The  boiling  is  continued  a few  minutes  and,  finally,  the  ley  is 
poured  upon  a filter,  and  the  filtrate  is  collected  in  the  bottle  from 


§ 204.] 


ACIDIMETRY. 


491 


TABLE  IV. 

Showing  the  percentages  of  hydrated  acid  corresponding  to  various 
specific  gravities  of  aqueous  Acetic  Acid , by  Mohr. 


Specific 

gravity. 

Percentage  of 
hydrated  acid. 

Specific 

gravity. 

Percentage  of 
hydrated  acid. 

Specific 

gravity. 

Percentage  of 
hydrated  acid. 

Specific  ; 
gravity. 

Percentage  of 
hydrated  acid. 

Specific 

gravity. 

Percentage  of 
hydrated  acid. 

1 0635 

100 

1 0735 

80 

1-067 

60 

1 051 

40 

1-027 

20 

1 0655 

99 

1 0735 

79 

1-066 

59 

1 050 

39 

1 026 

19 

1 -0670 

98 

1 0732 

78 

1-066 

58 

1-049 

38 

1 025 

18 

1-0680 

97 

, 1 0732 

77 

1 065 

57 

1048 

37 

1 024 

17 

1 -0690 

96 

: 1 0730 

76 

1064 

56 

1-047 

36 

1023 

16 

1 -0700 

95 

1 0720 

75 

1064 

55 

1046 

35 

1022 

15 

1 0706 

94 

1 -0720 

74 

1 063 

54 

1045 

34 

1 020 

14 

1-0708 

93 

1 0720 

73 

1063 

53 

1-044 

33 

1-018 

13 

10716 

92 

1-0710 

72 

1 062 

52 

1042 

32 

1-017 

12 

1-0724 

91 

10710 

71 

1061 

51 

1-041 

31 

1-016 

11 

1 -0730 

90 

1-0700 

70 

1060 

50 

1-040 

30 

1015 

10 

1 -0730 

89 

1 0700 

69 

1 059 

49 

1 039 

29 

2 013 

9 

1 0730 

88 

1 -0700 

68 

1-058 

48 

1-038 

28 

1-012 

8 

1 0730 

87 

1 -0690 

67 

1056 

47  ' 

1 -033 

27 

1-010 

7 

1 -0730 

86 

1 0690 

66 

1-055 

46 

1 035 

26 

^ 1-008 

6 

1 -0730 

85 

1 -0680 

65 

1-055 

45 

1034 

25 

1007 

5 

1 -0730 

84 

1 -0680 

64 

1-054 

44 

1 -033 

24 

1-005 

4 

1 -0730 

83 

1 0680 

63 

1 053 

43 

1-032 

23 

1-004 

3 

1-0730 

82 

1-0670 

62 

1 -052 

42 

1 -031 

22 

1-002 

2 

1 -0732 

81 

1-0670 

61 

1-051 

41 

1-029 

21 

1-001 

1 

which  it  is  to  be  used.  Care  should  be  taken  to  bring  upon  the  filter 
some  of  the  excess  of  lime  that  is  suspended  in  the  liquid,  so  that  the 
latter  may  acquire  no  carbonic  acid  from  the  air.  This  clear  liquid 
thus  obtained  is  a potash-lye  containing  lime  in  solution.  If  exposed 
to  the  air,  the  carbonic  acid  that  is  absorbed  separates  as  carbonate  of 
lime,  leaving  the  liquid  perfectly  caustic. 

It  now  remains  to  determine  with  the  greatest  accuracy,  1st,  the  vol- 
ume of  alkali  which  neutralizes  a cubic  centimetre  of  the  acid,  and,  2d, 
the  amount  of  SO;}  contained  in  a cubic  centimetre  of  the  latter. 

As  a means  of  recognizing  the  point  of  neutralization,  tincture  of 
cochineal  possesses  great  advantages  over  solution  of  litmus.  The 
knowledge  of  this  fact  is  due  to  Luckow,  who  has  detailed  its  applica- 
tion in  Pour,  fur  Pract.  Chem .,  Ixxxiv.,  p.  424.  Tincture  of  cochineal 
is  prepared  by  digesting  and  frequently  agitating  three  grammes  of  pul- 
verized cochineal  in  a mixture  of  50  cubic  centimetres  of  strong  alcohol 
with  200  c.  c.  of  distilled  water,  at  ordinary  temperatures,  for  a day  or 
two.  The  solution  is  decanted,  or  filtered  through  Swedish  paper. 

The  tincture  thus  prepared  has  a deep  ruby-red  color.  On  gradually 
diluting  with  pure  water  (free  from  ammonia),  the  color  becomes  orange 
and  finally  yellowish-orange.  Alkalies  and  alkali-earths  as  well  as  their 
carbonates  change  the  color  to  a carmine  or  violet-carmine.  Solutions 
of  strong  acid  and  acid  salts  make  it  orange  or  yellowish-orange. 


492 


SPECIAL  PART. 


To  determine  the  volumetric  relation  of  the  alkali  and  acid , a given 
volume  of  the  latter,  e.  g.  20  c.  c.,  is  measured  off  into  a wide-mouthed 
flask,  ten  drops  of  cochineal-tincture,  and  about  150  c.  c.  of  water  are 
added — the  alkali  is  now  allowed  to  flow  in  from  a burette,  until  the 
yellowish  liquid  in  the  flask,  suddenly,  and  by  a single  drop,  acquires  a 
violet-carmine  tinge. 

In  nicer  determinations,  it  is  important  to  bring  the  liquid  each  time 
to  a given  volume,  by  adding  water  after  the  neutralization  is  nearly  fin- 
ished. For  this  purpose,  two  or  more  flasks  of  equal  capacity  are  se- 
lected, and  on  the  outside  of  each  a strip  of  paper  is  gummed  to  indicate 
the  level  of  the  proper  amount  of  liquid,  e.  g.  200  c.  c.  The  same 
amount  of  coloring  matter  being  thus  always  diffused  in  the  same  vol- 
ume of  the  same  water,  the  errors  of  varying  dilution  and  varying 
amount  of  ammonia  (which  is  rarely  absent  from  distilled  water)  are 
avoided.  The  contents  of  one  flask,  in  which  the  neutralization  has 
been  satisfactorily  effected,  may  be  kept  as  a standard  of  color  for  the 
succeeding  trials,  as  the  tint  remains  constant  for  hours,  being  unaffected 
by  the  absorption  of  carbonic  acid.  The  greatest  convenience  and  ac- 
curacy of  measurement  are  obtained  by  using  burettes  provided  with 
Erdmann’s  swimmer  (See  p.  30.) 

When  three  or  four  accordant  results  have  been  obtained,  the  average 
is  taken  as  expressing  the  relative  strength  of  the  acid  and  alkali. 

To  ascertain  the  absolute  standard , weigh  off  in  a small  platinum  cru- 
cible about  0*8  grm.  of  pure  carbonate  of  soda,  ignite  to  dull  redness, 
cool  and  weigh  accurately  : bring  the  crucible  with  its  contents  into  one 
of  the  wide-mouthed  flasks  and  let  flow  from  the  burette  a slight  excess, 
e.  g.  50  c.  c.,  of  standard  acid.  The  solution  of  carbonate  of  soda  is 
facilitated  by  warming,  and,  finally,  the  contents  of  the  flask  are  gently 
boiled  for  several  minutes  to  expel  carbonic  acid.  The  solution  is  now 
allowed  to  becom q perfectly  cold , then  add  ten  drops  of  cochineal  and 
lastly  the  standard  alkali  to  neutralization,  diluting  to  the  proper  vol- 
ume. 

To  illustrate  the  accuracy  of  the  process  and  the  calculations  employed, 
the  following  actual  data  may  be  useful.  The  normal  acid  was  made  by 
diluting  50  c.  c.  of  oil-of-vitriol  to  the  volume  of  ten  litres  and  had  half 
the  strength  above  recommended.  The  alkali  w$s  from  a stock  on  hand 
and  more  dilute  than  necessary. 

Relation  of  acid  to  alkali. 

Exp.  I.,  20  c.  c.  S03=32*8  c.  c.  KO,  or  1 : 1*64 

Exp.  II.,  20  c.  c.  SO,  = 32*8  c.  c.  KO,  or  1 : 1*64 

Exp.  III.,  40  c.  c.  S03  = 65*7  c.  c.  KO,  or  1 : 1*6425 

We  have  accordingly: 

1 c.  c.  S03  = l*64  c.  c.  KO  and  1 c.  c.  K0=0*60976  c.  c.  SO, 

Absolute  strength  of  acid  and  alkali. 

Exp.  I.  0*4177  grm.  of  carbonate  of  soda  were  treated  with  44*2  of  SOs. 
To  neutralize  the  excess  of  the  acid  were  required  3*8  c.  c.,  KO,  which  cor- 
respond to  2*32  c.  c.  SO,(3*8  X 0*60976).  Deducting  this  from  the  total 
amount  of  acid  (44*2—2*32)  we  have  41*88  c.  c.  of  acid,  equivalent  to  the 
carbonate  of  soda  taken. 


§ 204] 


ACIDIMETRY. 


493 


41*88  c.  c.  solution  of  S03  = 0*4197  grm.  NaO  C02. 

Exp.  II.  0*4126  grm.  NaO  Co2  treated  with  44  c.  c.  S03  required 
4*28  c.  c.  KO.  4*28x  0*60976=  2*61  c.  c.  S03.  44-2*61=41*39 

c.  c.  S03. 

41*39  c.  c.  solution  of  SO3  = 0*4126  grms.  NaO  C02. 

It  is  convenient  to  calculate  how  much  acid  corresponds  to  53  deci- 
grammes of  carbonate  of  soda,  since  the  relation  of  any  other  substance 
to  the  acid  is  then  obtained  by  substituting  its  equivalent  number  for  53 
(the  equivalent  of  NaO  C02),  in  the  following  equation,  thus : 

grms.  NaO  C02  c.  c.  S03 

T.  *0*4177  : 0*53  : : 41*88  : 53*14 

II.  0*4126:0*53  ::  41*39:53*17 

Accordingly  0*53  grm.  NaO  C02  neutralize  53*155  c.  c.  S03. 

If,  for  example,  the  solutions  are  employed  for  nitrogen  estimations 
(§  185),  we  learn  how  much  nitrogen  corresponds  to  1 c.  c.  of  acid,  by  the 
following  proportion : 

c.  c.  S03  grm.  N. 

73*1^71  : : 0*140  : 0*00263? 

We  may  then  write  on  the  label  of  the  acid  bottle  the  following  data 
for  calculation. 

1 c.  c.  KO  =0*60976  c.  c.  S03. 

1 c.  c.  S03  =1*64  c.  c.  KO. 

1 c.  c.  S03  =0*002634  grm.  N. 

According  to  Luckow,  cochineal  is  quite  indifferent  to  carbonic  and 
sulphydric  acids,  carminic  acid  being  stronger  than  these.  This  is  prac- 
tically true  for  solutions  of  considerable  strength.  Hence  a Normal  Al- 
kali for  technical  analysis  may  be  prepared  by  simply  dissolving  53  grms. 
of  pure  and  anhydrous  carbonate  of  soda  in  a,  litre  of  water.  To  make  a 
normal  acid  mix  1050  c.  c.  of  water  with  60  grm.  of  concentrated  sul- 
phuric acid,  let  cool  and  ascertain  as  just  described  how  many  c.  c.  of 
this  acid  neutralize  50  c.  c.  of  normal  carbonate  of  soda.  Suppose  48*6 
c.  c.  are  required,  then  50  — 48*6  = 1*4  c.c.  of  water  must  be  added  to  every 
48*6  c.  c.  of  acid  to  make  it  normal.  For  a litre  of  normal  acid  48*6  x 
20  972  c.  c.  of  this  acid  and  28  c.c.  of  water  should  be  mixed.  As  it  is 

difficult  to  do  this  with  accuracy,  we  ascertain  how  much  water  is 
needed  to  bring  1000  c.  c.  of  the  acid  to  the  normal  strength. 

o o 

972  : 1000  : : 28  : a; 
x = 28*8 

Fill,  therefore,  a flask  holding  a litre  to  the  mark  with  the  acid,  add 
from  a burette  28*8  c.  c.  of  water  and  mix.  Test  finally  the  acid  against 
the  alkali  to  be  certain  that  equal  volumes  neutralize  each  other. 

Decinormal  solutions  may  be  prepared  by  diluting  100  c.  c.  of  the  normal 
solutions  to  a litre,  or  taking  5*3  grms.  of  carbonate  of  soda  as  the  starting 
point.  In  the  neutralization  it  is  not  needful  to  expel  carbonic  acid  by 
boiling.  The  influence  of  the  latter  is  however  at  once  seen  when  a caustic 
and  carbonated  alkali  are  operated  with  side  by  side.  In  case  of  the 
former,  the  point  of  neutralization  (or  rather  of  supersaturation),  is 


494 


SPECIAL  PART. 


L§  204. 


shown  by  a prompt  and  decisive  change  from  a tint  in  which  orange 
predominates,  to  one  in  which  this  disappears  and  violet  is  most  marked. 
In  presence  of  carbonic  acid  the  change  is  somewhat  gradual,  and  though 
a red  color  is  produced  it  is  modified  by  an  orange  tint,  even  in  pres- 
ence of  a large  excess  of  alkali.  Hence,  it  is  to  be  recommended,  espe- 
cially in  nice  investigations,  to  employ  a caustic  alkali.  A trifile  less 
of  it  will  be  found  needful  to  neutralize  a given  volume  of  acid,  than  is 
required  of  a carbonated  solution,  and  no  doubt  will  exist  as  to  the  point 
of  saturation.* 

This  indifference  towards  carbonic  acid  is  a great  advantage  in  nice 
analyses,  in  that  the  time  consumed  for  effecting  neutralization  is 
without  influence  on  the  result.  When  litmus  is  used  and  the  point 
of  neutralization  is  reached,  a short  exposure  to  the  air  suffices  to  redden 
the  liquid  again.  If  the  operator  is  obliged  to  proceed  slowly,  he  will 
require  somewhat  more  alkali  than  when  he  operates  rapidly ; a portion 
of  it  being  neutralized  by  atmospheric  carbonic  acid.  With  cochineal, 
the  result  is  independent  of  the  small  amount  of  carbonic  acid  that  can 
come  from  the  air.  The  permanence  of  the  color  also  allows  several  ti- 
trations to  be  compared  directly  together. 

Another  advantage  of  cochineal  is,  that  its  solution,  prepared  as  above 
described,  may  be  preserved  indefinitely  in  closed  vessels,  without  de- 
colorization  or  alteration. 

b.  The  Actual  Analysis. — It  is  only  necessary  to  weigh  or  measure  off 
a quantity  of  the  acid  to  be  examined  and  ascertain  how  much  standard 
alkali  is  required  for  its  neutralization,  as  has  been  detailed.  The  selec- 
tion of  the  alkaline  fluid  depends,  of  course,  entirely  upon  the  quantity 
of  acid  to  be  neutralized.  The  neutralization  of  the  weighed  or  measured 
acid  fluid  should  take  about  15 — 30  c.  c. 

In  scientific  investigations,  I recommend  the  weighing  of  indeterminate 
quantities  of  the  acid  fluid,  as  the  weighing  of  definite  quantities  on  a 
chemical  balance  is  troublesome,  and  the  trouble  of  calculation  is  not 
worth  mentioning.  Suppose,  for  instance,  you  have  weighed  off  4’5 
grm.  of  a dilute  acetic  acid,  and  used  25  c.  c.  normal  solution  of  soda  to 
neutralize  this,  you  find  by  the  proportion, 

1000  : 25  : : 60  (eq.  C4  II4  04)  : *;  a?=l-5, 

that  1*5  grm.  of  hydrated  acetic  acid  are  contained  in  the  weighed 
quantity  of  the  dilute  acid  ; and  another  proportion,  viz., 

4-5  : 1-5  ::  100  : x;  z=33*33 

gives  the  percentage  of  hydrated  acetic  acid  contained  in  the  analyzed 
fluid.  Or,  the  calculation  may  also  be  made  as  follows: — 

4*5  grm.  of  the  acetic  acid  examined  having  required  25  c.  c.  of  normal 

* Collier  has  made  some  experiments  with  a sulphuric  acid  containing  25  c.  c. 
oil  of  vitriol  to  the  litre,  and  a solution  of  carbonate  of  soda,  and  he  found,  when 
C02  was  expelled  by  boiling,  that  10  c.  c.  SO?  = 7'06  and  7 '67  c.  c.  of  NaO  C02; 
when  C02  was  not  expelled,  10  c.  c.  S03=7'68  and  7 '7.  These  results  are  as 
good  as  identical.  In  standarding  the  much  weaker  acid  above  mentioned, 
he  obtained  for  it  a value  slightly  too  low  when  C02  was  not  removed.  0'53 
grm.  NaO  C02  required  in  this  case  but  53  05  c.  c.  S03,  instead  of  53  155 
as  in  the  other  instances.  This  is  a very  slight  difference  and  not  appreciable 
perhaps  with  ordinary  burettes,  but  it  is  a constant  and  perceptible  differ- 
ence. What  is  of  more  importance  is  the  uncertainty  as  to  the  point  of  neu- 
tralization. 


204.] 


ACIDIMETRY. 


495 


solution  of  soda  for  neutralization,  how  much  would  6 grm.  (i.e.  the 
weight  of  y1^  eq.  grm.  hydrated  acetic  acid)  require? 

4*5  : 6 : : 25  : a? ; a;=33-33 

It  is  evident  that  in  this  case  the  number  of  c.  c.  found  as  x expresses 
the  percentage  of  hydrated  acetic  acid,  since  100  c.  c.  of  normal  solution 
of  soda  correspond  to  y1^-  eq.  grm.  pure  hydrated  acid,  i.  e.  acetic  acid  of 
100  per  cent. 

In  technical  analyses  it  is  more  convenient  if  the  number  of  c.  c.  or 
half  c.  c.  used  of  the  normal  solution  of  soda  expresses  directly  the  per- 
centage of  hydrated  or  anhydrous  acid  contained  in  the  examined  fluid. 
For  this  purpose,  the  T*y  or  -^y  equivalent  number  (H  = l)  of  grammes 
of  the  anhydrous  or  hydrated  acid,  are  weighed  off  according  as  the 
number  of  c.  c.  or  half  c.  c.  of  normal  alkali  used,  are  to  express  the 
percentage  of  hydrated  or  anhydrous  acid  contained  in  the  analyzed 
fluids. 

The  following  are  the  quantities  for  the  more  common  acids  : — 


Sulphuric  acid 

■y y Eq.  number 
of  grammes. 

. 4*0 

Eq.  number 
of  grammes. 

. 2-00 

Hydrated  sulphuric  acid 

. 4-9 

. 2-45 

Nitric  acid 

. 5-4 

. 2-70 

Hydrated  nitric  acid 

. 6*3 

. 3-15 

Hydrochloric  acid  . 

. 3-646 

. 1-823 

Oxalic  acid 

. 3-6 

. 1-80 

Crystallized  oxalic  acid 

. 6-3 

. 3-15 

Acetic  acid 

. 5-1 

. 2-55 

Hydrated  acetic  acid 

. 6-0 

. 3-00 

Tartaric  acid  . 

. 6-6 

. 3-30 

Hydrated  tartaric  acid 

. 7-5 

. . 3*75 

But,  as  the  weighing  of  definite  small  quantities  would  hardly  be 
accurate  enough,  it  is  preferable  to  weigh  oft’  the  half  eq.  grm.  of  the 
acids  ( i . e.  20  or  24'5  grm.  of  sulphuric  acid,  according  to  whether  it  is 
intended  to  find  the  percentage  of  anhydrous  or  of  hydrated  acid;  18’23 
of  hydrochloric  acid,  &c.)  in  a measuring  flask  holding  500  c.  c.,  add 
water  cautiously,*  allow  to  cool  if  necessary,  fill  up  with  water  to  the 
mark,  shake,  and  then  remove,  by  means  of  the  pipette,  100  or  50  c.  c., 
according  to  whether  T’y  or  gV  eq.  grm.  acid  is  to  be  used. 

c.  Deviations  from  the  preceding  method  of  Analysis. 

a.  It  is  often  preferred  to  have  the  alkali  of  such  a strength  that  the 
c.  c.  or  the  half  c.  c.  employed  to  neutralize  a round  number  of  grm.  or 
c.  c.  of  an  aqueous  acid  may  express  at  once  the  percentage  of  real  acid. 
For  instance,  if  we  add  20  c.  c.  water  to  1000  c.  c.  normal  soda  solution, 
these  1020  c.  c.  will  saturate  51  (1  eq.)  grm.  anhydrous  acetic  acid, 
1000  c.  c.  therefore  saturate  50  grm.  Hence  if  we  take  10  grm.  of  vine- 
gar (10  c.  c.  will  do  instead,  as  the  specific  gravity  of  vinegar  scarcely 
differs  from  that  of  water),  and  add  our  diluted  solution  of  soda  to  satu- 

* In  the  case  of  concentrated  sulphuric  acid,  the  flask  must  be  half  full  of 
water  before  the  acid  is  weighed  into  it. 


SPECIAL  PART. 


496 


[§  205. 


ration,  the  c.  c.  used,  divided  by  2,  will  express  the  percentage  of  anhy- 
drous acetic  acid  in  the  specimen  of  vinegar  examined.* 

0.  If  the  color  of  a fluid  conceals  the  change  of  the  dissolved  cochineal, 
or  if  salts  of  iron  be  present,  we  use  red  litmus  or  turmeric  paper  to  hit 
the  point  of  neutralization,  i.  e.,  we  add  alkali  till  a strip  of  test  paper 
dipped  in  just  indicates  a weak  alkaline  reaction.  In  this  case  more 
alkali  will  be  employed  than  when  cochineal  can  be  used  in  solution, 
and  in  exact  determinations  it  may  be  worth  while  to  rectify  the  error 
by  a correction.  This  may  be  done  by  taking  a like  quantity  of  water 
and  adding  soda  solution,  till  the  fluid  just  gives  a reaction  on  the  test 
paper  in  question,  as  strong  as  was  obtained  at  the  close  of  the  first  ex- 
periment. The  quantity  of  alkali  used  is  of  course  to  be  deducted  from 
the  quantity  employed  in  the  first  experiment. 

d.  Application  of  the  Acidimetric  principle  to  the  determination  of 

combined  acids. 

The  acidimetric  principle  may  often  be  employed  also  for  the  deter- 
mination of  acids  in  combination  with  bases,  if  solution  of  carbonate  of 
soda  precipitates  the  latter  completely,  and  in  a state  of  purity.  Tor 
instance,  acetic  acid  in  iron  mordant,  or  in  verdigris,  may  be  estimated 
in  this  way,  bv  the  following  process: — Precipitate  with  a measured 
quantity  of  normal  solution  of  carbonate  of  soda  in  excess,  boil,  filter, 
wash,  concentrate  the  filtrate,  add  cochineal  and  normal  acid  to  neu- 
tralization. Subtract  the  c.  c.  of  standard  acid  used,  from  the  c.  c. 
of  soda  solution  consumed  in  the  experiment : the  difference  expresses 
the  quantity  of  soda  solution  neutralized  by  the  acid  contained  in  the 
substance,  in  combination  as  well  as  in  the  free  state.  Of  course,  cor- 
rect results  can  be  expected  only  if  no  basic  salt  has  been  thrown  down 
by  the  soda  solution. 

e.  Determination  of  combined  acids  by  Gibbs ’ method.  See  § 149,  ii., 

c , 7,  p.  330. 


Modification  of  the  common  Acidimetric  Method  (Kiefer-)-). 

§ 205. 

Instead  of  estimating  free  acid  by  a solution  of  soda  of  known  strength, 
and  determining  the  neutralization  point  by  means  of  cochineal  tincture, 
an  ammoniacal  solution  of  oxide  of  copper  may  be  used  for  the  pur- 
pose, in  which  case  the  neutralization  point  is  known  by  the  turbidity 
observed  as  soon  as  the  free  acid  present  is  completely  neutralized.  The 
copper  solution  is  prepared  by  adding  to  an  aqueous  solution  of  sulphate 
of  copper,  solution  of  ammonia  until  the  precipitate  of  basic  salt  which 
forms  at  first  is  just  redissolved.  After  determining  the  strength  of  the 
solution  by  normal  sulphuric  or  hydrochloric  acid  (not  oxalic),  it  maybe 
emploved  for  the  estimation  of  all  the  stronger  acids  (with  the  exception 
of  oxalic  acid),  provided  the  fluids  are  clear.  The  basic  salt  of  copper, 
in  the  precipitation  of  which  the  final  reaction  consists,  is  not  insoluble 
in  the  ammonia  salt  formed,  and  its  solubility  depends  on  the  degree  of 
concentration,  and  on  the  presence  of  other  salts,  especially  of  ammonia 
salts  (Carey  Lea];).  Hence  the  method  cannot  boast  of  scientific 

* Zeitschrift  f.  analyt.  Chem.  1,  253.  f Annal  d.  Chem.  u.  Pharm.  93,  386. 

X Chem.  News,  4,  195. 


§ 206.] 


ALKALIMETRY. 


497 


TABLE  I. 


Percentages  of  Anhydrous  Potassa  corresponding  to  different  specific 
gravities  of  solution  of  potassa. 


Dalton. 

Tiinnermann  {at  15°). 

Specific 

gravity. 

Percentage 
of  anhydrous 
potassa. 

Specific 

gravity. 

Percentage 
of  anhydrous 
potassa. 

Specific 

gravity. 

Percentage 
of  anhydrous 
potassa. 

1-60 

46  7 

1 -3300 

28-290 

1-1437 

14-145 

1-52 

42-9 

1 3131 

27-158 

1-1308 

13  013 

1-47 

39  6 

1 -2966 

26  027 

1-1182 

11  -882 

1-44 

36-8 

1 -2803 

24-895 

1 -1059 

10-750 

142 

34  4 

1 -2648 

23-764 

1-0938 

9-619 

1-39 

32  4 

1-2493 

22-632 

1-0819 

8-487 

1-36 

29  4 

1 -2342 

21  -500 

1 -0703 

7-355' 

1*33 

26  3 

1 -2268 

20-935 

1-0589 

6-224 

1-28 

23  4 

1-2122 

19-803 

1 -0478 

5-002 

1-23 

19-5 

1-1979 

18-671 

1 -0369 

3-961  ' 

1*19 

16  2 

1-1839 

17-540 

1 0260 

2-829 

115 

13  0 

1 -1702 

16-408 

1 -0153 

1-697 

111 

9 5 

1-1568 

15-277 

1 -0050 

0-5658 

106 

4*7 

TABLE  II. 


Percentages  of  Anhydrous  Soda  corresponding  to  different  specific 
gravities  of  solution  of  soda. 


Dalton. 

Tunnermann  {at  15°). 

Specific 

gravity. 

Percentage 
of  anhy- 
drous soda. 

Specific 

gravity 

Percentage 
of  anhy- 
drous soda. 

Specific 

gravity. 

Percentage 
of  anhy- 
drous soda. 

Specific 

gravity. 

Percentage 
of  anhy- 
drous soda 

1-56 

41-2 

1-4285 

30  220 

1 -2982 

20-550 

1 -1528 

10-275 

1-50 

36-8 

1 -4193 

29-616 

1-2912 

19-945 

1 -1428 

9-670 

1-47 

34  0 

1-4101 

29-011 

1 -2843 

19-341 

1 -1330 

9 066 

1-44 

31  0 

1-4011 

28-407 

1 -2775 

18-730 

1 1233 

8-462 

1-40 

29  0 

1-3923 

27-802 

1-2708 

18-132 

11137 

7-857 

1-36 

26  0 

1-3836 

27-200 

1 -2642 

17-528 

1 -1042 

7 253 

1-32 

23  0 

1 -3751 

26-594 

1 -2578 

16-923 

1 -0948 

6-648 

1-29 

190 

1-3668 

25-989 

1 -2515 

16-319 

1 -0855 

6 044 

1-23 

160 

1-3586 

25  385 

1 -2453 

15-714 

1 0764 

5-440 

1-18 

13-0 

1 -3505 

24-780 

1 -2392 

15-110 

1 -0675 

4-835 

1-12 

9-0 

1 -3426 

24176 

1 -2280 

14-506 

1 0587 

4-231 

106 

4-7 

1 3349 

23-572 

1 -2178 

13-901 

1 0500 

3-626 

1 -3273 

22-967 

1 -2058 

13-297 

10414 

3 022 

1-3198 

22-363 

1-1948 

12-692 

1 0330 

2-448 

1-3143 

21  -894 

1-1841 

12-088 

1 0246 

1-813 

1-3125 

21-758 

1-1734 

11-484 

1-0163 

1-209 

1 *3053 

21  154 

1-1630 

10-879 

1 0081 

0 604 

32 


498 


SPECIAL  PART. 


[§  206. 


TABLE  III. 

Percentages  of  Ammonia  (N  H ) corresponding  to  different  specific 
gravities  of  solution  of  ammonia  at  16°  (J.  Otto). 


Specific 

gravity. 

Percentage 

of 

ammonia. 

Specific 

gravity. 

Percentage 

of 

ammonia. 

Specific 

gravity. 

Percentage 

of 

ammonia. 

0-9517 

12  000 

0-9607 

9 625 

0-9697 

7-250 

0 9521 

11-875 

0-9612 

9-500 

0-9702 

7 125 

0-9526 

11-750 

0.9616 

9 375 

0-9707 

7-000 

0-9531 

11-625 

0-9621 

9-250 

0-9711 

6-875 

0-9536 

11-500 

0 9626 

9 125 

0-9716 

6-750 

0-9540 

11-375 

0-9631 

9-000 

0-9721 

6-625 

0-9545 

11-250 

0-9636 

8-875 

0-9726 

6-500 

0-9550 

11-125 

0-9641 

8-750 

0-9730 

6-375 

0 9555 

11000 

0-9645 

8-625 

0-9735 

6-250 

0-9556 

10-950 

0-9650 

8 500 

0-9740 

6125 

0-9559 

10-875 

0-9654 

8-375 

0-9745 

6 000 

0-9564 

10-750 

0-9659 

8 250 

0-9749 

5-875 

0-9569 

10-625 

0-9664 

8-125 

0-9754 

5-750 

0-9574 

10-500 

0-9669 

8-000 

0-9759 

5-625 

0-9578 

10-375 

0-9673 

7-875 

0-9764 

5-500 

0-9583 

10-250 

0-9678 

7-750 

0-9768 

5-375 

0-9588 

10-125 

0-9683 

7-625 

0-9773 

5-250 

0-9593 

10-000 

0-9688 

7-500 

0-9778 

5-125 

0-9597 

0-9602 

9-875 

9-750 

0-9692 

7-375 

0-9783 

5-000 

accuracy,  but  as  the  variations  occasioned  by  the  causes  mentioned  are 
inconsiderable,*  the  process  retains  its  applicability  to  technical  purposes, 
for  which,  indeed,  it  was  originally  proposed.  This  method  is  of  especial 
value  in  cases  in  which  free  acid  is  to  be  determined  in  presence  of  a 
neutral  metallic  salt  with  acid  reaction — e.g .,  free  sulphuric  acid  in 
mother-liquors  of  sulphate  of  copper  or  sulphate  of  zinc,  &c.  It  is  advis- 
able to  determine  the  strength  of  the  ammoniacal  copper  solution  anew 
before  every  fresh  series  of  experiments. 

3.  Alkalimetry. 

A.  Estimation  of  Potassa,  Soda,  or  Ammonia,  from  the  Specific 
Gravity  of  their  Solutions. 


§ 206. 

In  pure  or  nearly  pure  solutions  of  hydrated  soda  or  potassa,  or  of 
ammonia,  the  percentage  of  alkali  may  be  estimated  from  the  specific 
gravity  of  the  solution. 

B.  Estimation  of  the  total  Amount  of  Carbonated  and  Caustic 
Alkali  in  crude  Soda  and  in  Potashes. 

The  “ soda  ash  ” of  commerce  is  a crude  carbonate  of  soda — the 


* Compare  my  experiments  on  the  subject  in  the  Zeitschrift  f.  analyt.  Chem. 
1,  108. 


ALKALIMETRY. 


499 


§ 207.] 

6<  potashes  ” and  u pearlash  ” a crude  carbonate  of  potash.  The  com- 
mercial value  of  these  articles  depends  on  the  percentage  of  alkaline 
carbonate  (or  caustic  alkali)  that  they  contain,  which  is  very  variable. 

I.  Volumetric  Methods. 

Method  of  Descroizilles  and  Gay-Lussac,  slightly  modified. 

§ 207. 

The  principle  of  this  method  is  the  converse  of  that  on  which  the 
acidimetric  method  described  § 204,  is  based,  i.e.,  if  we  know  the  quan- 
tity of  an  acid  of  known  strength,  required  to  saturate  an  unknown 
quantity  of  caustic  potassa  or  soda,  or  of  carbonate  of  potassa  or  soda, 
we  may  readily  calculate  from  this  the  amount  of  alkali  present. 

For  technical  analyses  we  may  employ  the  normal  sulphuric  acid, 
p.  493. 

For  the  analysis  we  may  conveniently  weigh  off  such  a quantity  of 
the  substance  that  the  number  of  c.  c.  of  acid  required  to  neutralize  it 
shall  directly  express  its  percentage  of  the  alkali  or  carbonate  sought. 

The  proper  quantities  of  the  compounds  of  potassa  and  soda  to  em- 
ploy are  -*g  Eq.  (H  =1)  expressed  in  grms.,  viz. : — 


Potassa,  KO 4*7 1 1 grm. 

Hydrate  of  potassa,  KO,  HO 5*611  “ 

Carbonate  of  potassa,  KO,  C02 6*911  “ 

Bicarbonate  of  potassa,  KO,  HO,  2 C02 10*011  “ 

Soda,  NaO 3*100  “ 

Hydrate  of  soda,  NaO  HO 4*000  “ 

Carbonate  of  soda  (dry)  NaO  CO, 5*300  “ 

Crystallized  carbonate  of  soda,  NaO  C02,  10  HO 14*300 

Bicarbonate  of  soda,  NaO  HO  2 C02 8*400  “ 


With  regard  to  the  examination  of  pearlash  by  this  method , the  follow^ 
ing  points  deserve  attention  : — 

The  various  sorts  of  potash  of  commerce  contain,  besides  carbonate 
of  (and  caustic)  potassa, 

a.  Neutral  salts  ( e.g .,  sulphate  of  potassa,  chloride  of  potassium). 

b.  Salts  with  alkaline  reaction  ( e.g .,  silicate  of  potassa,  phosphate  of 
potassa). 

c.  Admixtures  insoluble  in  water , more  especially  carbonate,  phos- 
phate, and  silicate  of  lime. 

The  salts  named  in  a exercise  no  influence  upon  the  results,  but  not 
so  those  named  in  b and  c . Those  in  c may  be  removed  by  filtration  ; 
but  the  admixture  of  the  salts  named  in  b constitutes  an  irremediable, 
though  slight  source  of  error : — that  is  to  say,  if  it  is  desired  to  confine 
the  determination  to  the  caustic  and  carbonated  alkali.  But  as  regards 
the  estimation  of  the  value  of  pearlash  for  many  purposes,  the  term 
error  cannot  be  applied  ; as,  for  instance,  in  the  preparation  of  caustic 
potassa,  by  boiling  the  solution  with  lime,  the  alkali  combined  with 
silicic  acid  and  with  phosphoric  acid  is  converted,  like  the  carbonate, 
into  the  caustic  state. 

If  you  are  not  satisfied  with  finding  the  percentage  of  available  alkali, 
but  desire  also  to  know  whether  the  remainder  consists  simply  of 


500 


SPECIAL  PART. 


[§  208. 

foreign  salts,  or  whether  water  is  also  present,  the  determination  of  the 
latter  substance  must  precede  the  alkalimetric  examination.  The  same 
remark  applies  also  to  soda. 

With  regard  to  the  examination  of  soda  by  this  method , the  following 
points  deserve  attention  : — 

The  soda  of  commerce,  prepared  by  Leblanc’s  method,  contains,  be- 
sides carbonate  of  soda,  always,  or  at  least  generally,  hydrate  of  soda, 
sulphate  of  soda,  chloride  of  sodium,  silicate  and  aluminate  of  soda,  and 
not  seldom  also  sulphide  of  sodium,  hyposulphite  and  sulphite  of  soda.* 

The  three  last-named  substances  impede  the  process,  and  interfere 
more  or  less  with  the  accuracy  of  the  results.  Their  presence  is  ascer- 
tained in  the  following  way  : — 

a.  Mix  with  sulphuric  acid  ; a smell  of  sulphuretted  hydrogen  reveals 
the  presence  of  sulphide  of  sodium , with  which  hyposulphite  of  soda  is 
also  invariably  associated. 

b.  Color  dilute  sulphuric  acid  with  a drop  of  solution  of  permangan- 
ate of  potassa  or  chromate  of  potassa,  and  add  some  of  the  soda  under 
examination,  but  not  sufficient  to  neutralize  the  acid.  If  the  solution 
retains  its  color,  this  proves  the  absence  of  both  sulphite  and  hyposul- 
phite of  soda ; but  if  the  fluid  loses  its  color,  or  turns  green,  as  the  case 
may  be,  one  of  these  salts  is  present. 

c.  Whether  the  reactioh  described  in  b proceeds  from  sulphite  or 
hyposulphite  of  soda,  is  ascertained  by  supersaturating  a clear  solution 
of  the  sample  under  examination  with  hydrochloric  acid.  If  the  solu- 
tion, after  the  lapse  of  some  time,  becomes  turbid,  owing  to  the  separa- 
tion of  sulphur  (emitting  at  the  same  time  the  odor  of  sulphurous  acid), 
this  may  be  regarded  as  a proof  of  the  presence  of  hyposulphite  of  soda ; 
however,  the  solution  may,  besides  the  hyposulphite,  also  contain  sul- 
phite of  soda.  With  respect  to  the  detection  of  sulphite  of  soda  in  the 
presence  of  hyposulphite,  comp.  u Qual.  Anal.,”  p.  187. 

The  defects  arising  from  the  presence  of  the  three  compounds  in 
question  may  be  remedied  in  a measure,  by  igniting  the  weighed  sanple 
of  the  soda  with  chlorate  of  potassa,  before  proceeding  to  saturate  it. 
This  operation  converts  the  sulphide  of  sodium,  hyposulphite  of  soda, 
and  sulphite  of  soda  into  sulphate  of  soda.  But  if  hyposulphite  of  soda 
is  present,  the  process  serves  to  introduce  another  source  of  error,  as 
that  salt,  upon  its  conversion  into  sulphate  of  soda,  decomposes  an 
equivalent  of  carbonate  of  soda,  and  expels  the  carbonic  acid  of  the 
latter  [Na  O,  S202  + 40  (from  the  chlorate  of  potassa)  + Na  O,  C02= 
2 (Na  O,  S03)  + CO.J. 

The  presence  of  silicate  of  soda  and  of  aluminate  of  soda  may  be 
generally  recognized  by  the  separation  of  a precipitate  as  soon  as  the 
solution  is  saturated  with  acid.  If  you  intend  the  result  to  express  the 
quantity  of  carbonated  and  caustic  alkali  only,  the  presence  of  these 
two  bodies  becomes  a slight  source  of  error,  but  if  you  wish  to  estimate 
the  value  of  the  soda  for  many  purposes,  no  error  will  be  caused. 

§ 208. 

Method  of  Fr.  Mohr,  modified. 

Instead  of  estimating  the  alkalies  in  the  direct  way  by  means  of  an 


* Traces  of  cyanide  of  sodium  are  also  occasionally  found. 


ALKALIMETRY. 


501 


208.] 


acid  of  known  strength,  we  may  estimate  them  also,  as  proposed  first  by 
Fr.  Mohr,*  by  supersaturating  with  standard  acid,  expelling  the  car- 
bonic acid  by  boiling,  and  finally  by  determining  by  solution  of  soda  the 
excess  of  standard  acid  added. 

This  process  gives  very  good  results,  and  is  therefore  particularly 
suited  for  scientific  investigations.  It  requires  the  standard  fluids  men- 
tioned in  § 204,  viz.,  a standard  acid  and  standard  solution  of  soda.  Eadh 
of  these  fluids  is  filled  into  a Mohr’s  burette. 

The  process  is  as  follows  : — 

Dissolve  the  alkali  in  water,  and  add  a measured  quantity  of  tincture 
of  cochineal ; run  in  now  as  much  of  the  normal  acid  as  will  suffice  to 
impart  an  orange  tint  to  the  fluid  ; then  boil,  and  remove  the  last  traces 
of  carbonic  acid,  by  boiling,  shaking,  blowing  into  the  flask,  and  finally 
sucking  out  the  air. 

Now  add  standard  solution  of  soda,  drop  by  drop,  until  the  color  just 
appears  violet.  There  is  no  difficulty  in  determining  the  exact  point  at 
which  the  reaction  is  completed. 

If  the  standard  solution  of  soda  and  the  normal  acid  are  of  correspond- 
ing strength,  the  number  of  c.  c.  used  of  the  soda  solution  is  simply 
deducted  from  the  number  of  c.  c.  used  of  the  acid.  The  remainder  ex- 
presses the  quantity  of  acid  neutralized  by  the  alkali  in  the  examined 
sample.  If  the  two  standard  fluids  are  not  of  corresponding  strength, 
the  excess  of  acid  added,  and  subsequently  neutralized  by  the  soda  solu- 
tion, is  calculated  from  the  known  proportion  the  one  bears  to  the  other. 

If  yo  e(l-  number  (H=l)  of  grammes  have  been  weighed  of  the  alka- 
lies to  be  valued,  of  soda  accordingly,  5*3  grm.,  of  pearlash  6*91  grm., 
the  number  of  c.  c.  used  of  the  normal  acid  expresses  directly  the  per- 
centage of  carbonate  of  soda  or  carbonate  of  potassa  contained  in  the 
examined  sample ; since  100  c.  e.  of  the  normal  acid,  containing  T’F  eq. 
grm.  acid  will  just  suffice  to  neutralize  T*g-  eq.  grm.  pure  carbonate  of  soda 
or  carbonate  of  potassa. \ If  any  other  quantities  of  the  alkalies  have  been 
weighed  off,  a simple  calculation  will  give  the  result  in  the  desired 
form. 

To  make  this  simple  calculation  quite  clear  for  all  possible  cases, 
I select  one  of  the  most  complicated  kind,  proceeding  upon  the  supposi- 
tion that  the  soda  solution  is  not  of  corresponding  strength  with  the 
normal  acid,  but  that  2*2  c.  c.  of  the  soda  solution  neutralize-  1 c.  c.  of 
the  acid  ; and  that  instead  of  T*g-  eq.  grm.,  3*71  grm.  of  pearlash  have 
been  weighed  off. 

The  quantity  of  acid  added  was  48  c.  c. ; the  excess  required  4*3  c.  c. 
of  soda  solution  for  neutralization.  The  proportion 

2*2  : 1 ::  4*3  :x;  a=l-95 

shows  that  the  excess  of  acid  wasl*95  c.  c. ; 48  — 1'95  46-05  c.  c.  of  the 

acid  have  accordingly  been  consumed  by  the  pearlash.  The  proportion 

3-71  : 46*05  : : 6-91  (T\  eq.  KO,  C02)  : x:  a?=85*77 

shows  that  the  examined  pearlash  contains  85*77  per  cent,  of  the  pure 
carbonate. 

With  regard  to  certain  variations  from  the  ordinary  course  which  are 
occasionally  convenient,  comp.  p.  495. 


* Anna!,  d.  Chem.  u.  Pharm.  86,  129. 


f Of  100  per  cent. 


502 


SPECIAL  PART. 


[§  209, 


§ 209. 

There  now  still  remain  two  questions  to  be  considered,  which  are  of 
importance  for  the  estimation  of  the  commercial  value  of  potash  and  soda. 
The  first  concerns  the  separate  determination  of  the  caustic  alkali,  which 
the  sample  under  examination  may  contain  besides  the  carbonate;  the 
second,  the  determination  of  carbonate  of  soda  in  presence  of  carbonate 
of  potassa. 

C.  Determination  of  the  Caustic  Alkali  which  Commercial 
Alkali  may  contain  beside  the  Carbona'te. 

Many  kinds  of  potashes  and  crude  soda,  more  especially  the  latter, 
contain,  besides  alkaline  carbonate,  also  caustic  alkali ; and  the  chem- 
ist is  often  called  upon  to  determine  the  amount  of  the  latter ; as  it  is, 
for  instance,  by  no  means  a matter  of  indifference  to  the  soap-boiler 
how  much  of  the  soda  is  supplied  to  him  already  in  the  caustic  state. 
This  may  be  effected  as  follows  : 

Weigh  off  eq.  grm.  substance ; of  potashes  accordingly,  2073  grm., 
of  soda  15*9  grm. ; dissolve  in  water,  in  a flask  holding  300  c.  c.,  fillup 
to  the  mark,  .shake,  allow  the  fluid  to  deposit  out  of  contact  of  air,  and 
take  out  two  portions  of  100  c.  c.  each.  Determine  in  the  one  portion 
the  total  quantity  of  the  carbonated  and  caustic  alkali,  as  directed  § 
208  ; the  number  of  c.  c.  of  normal  acid  used  expresses  the  amount  of 
caustic  alkali -f- alkaline  carbonate,  in  per-cents,  of  the  latter.  Transfer 
the  other  portion  to  a measuring-flask  holding  300  c.  c.,  add  100  c.  c.  of 
water,  then  solution  of  chloride  of  barium  as  long  as  a precipitate  forms, 
add  water  up  to  the  mark,  shake,  allow  to  deposit  out  of  contact  of  air,* 
measure  off  100  c.  c.  of  the  supernatant  clear  fluid — which  now  contains 
caustic  baryta  in  corresponding  quantity  to  the  caustic  alkali' present  in 
the  sample — add  some  tincture,  of  cochineal,  then  normal  nitric  acid  (see 
§ 210),  to  acid  reaction.  Neutralize  the  excess  of  acid  bv  normal  solu- 
tion of  soda,  and  you  will  find  the  c.  c.  of  normal  acid  that  have  been  re- 
quired by  the  caustic  baryta.  Multiply  this  by  3 (as  only  of  the  sec- 
ond portion  has  been  employed  in  the  experiment)  ; the  result  gives  the 
percentage  of  caustic  alkali,  expressed  as  carbonate  of  soda  or  potassa. 
Deduct  this  number  from  the  percentage  obtained  in  the  first  experi- 
ment ; the  difference  gives  the  quantity  of  carbonate  of  potassa  or  soda 
present  as  such.  To  calculate  the  caustic  alkali  into  the  anhydrous  or 
hydrated  state,  it  is  only  necessary  to  multiply  by  the  numbers  given  in 
the  first  method. 

D.  Estimation  of  Carbonate  of  Soda  in  presence  of  Carbonate 
of  Potassa. 

Soda  being  much  cheaper  than  potash,  is  occasionally  used  to  adulter- 
ate the  latter.  The  common  alkalimetric  methods  not  only  fail  to  de- 
tect this  adulteration,  but  they  give  the  admixed  soda  as  carbonate  of 
potassa.  Many  processes'^  have  been  proposed  for  estimating  in  a sim- 
ple way  the  soda  contained  in  potash,  but  not  one  of  them  can  be  said 
to  satisfy  the  requirements  of  the  case. 


* Filtering  through  a dry  filter  causes  the  caustic  alkali  to  come  out  rather  toe 
low,  as  the  paper  retains  caustic  baryta  (A.  Muller,  Joum.  f.  prakt.  Chem.  83, 
384;  Zeitschrift  f.  analyt.  Cnem.  1,  84). 

f Comp.  Handworterbuch  der  Chemie,  2 Aufl.  I.  443. 


§ 210.] 


ESTIMATION  OF  ALKALINE  EARTHS. 


503 


The  following  tolerably  expeditious  process,  however,  gives  accurate 
results  : — Dissolve  6'  25  grm.  of  the  gently  ignited  pearlash  in  water, 
filter  the  solution  into  a quarter-litre  flask,  add  acetic  acid  in  slight  ex- 
cess, apply  a gentle  heat  until  the  carbonic  acid  is  expelled,  then  add  to 
the  fluid,  while  still  hot,  acetate  of  lead,  drop  by  drop,  until  the  forma- 
tion of  a precipitate  of  sulphate  of  lead  just  ceases  ; allow  the  mixture 
to  cool,  add  water  up  to  the  mark,  shake,  allow  to  deposit,  filter  through 
a dry  filter,  and  transfer  200  c.  c.  of  the  filtrate,  corresponding  to  5 grm. 
of  pearlash,  to  a |-litre  flask.  Add  sulphuretted  hydrogen  water  up  to 
the  mark,  and  shake.  If  the  acetate  of  lead  has  been  carefully  added, 
the  fluid  will  now  smell  of  sulphuretted  hydrogen,  and  no  longer  con- 
tain lead  ; in  the  contrary  case,  sulphuretted  hydrogen  gas  must  be  con- 
ducted into  it.  After  the  sulphide  of  lead  has  subsided,  filter  through 
a dry  filter.  Evaporate  50  c.  c.  of  the  filtrate  (corresponding  to  1 grm. 
of  pearlash)  with  addition  of  10  c.  c.  hydrochloric  acid,  of  1T0  sp.  gr., 
in  a weighed  platinum  dish,  to  dryness,  then  cover  the  dish,  heat,  and 
weigh  ; the  weight  found  expresses  the  total  quantity  of  chloride  of 
potassium  and  chloride  of  sodium  given  by  1 grm.  of  the-  pearlash. 
Estimate  the  potassa  and  soda  now  severally  in  the  indirect  way,  by 
determining  the  chlorine  volumetrically  (§  141,  I.,  b).  For  the  calcu- 
lation of  the  results,  see  § 197. 

4.  Estimation  of  Alkaline  Earths  by  the  Alkalimetric  Method. 

§ 210. 

Alkaline  earths,  in  the  caustic  state  or  in  the  form  of  carbonates, 
may  also  be  estimated  by  means  of  a standard  acid.  Standard  sul- 
phuric acid  may  be  used  for  the  estimation  of  magnesia  ; standard  nitric 
acid  for  that  of  baryta,  strontia,  and  lime.  To  prepare  1 litre  of  normal 
nitric  acid  you  require  a pure  dilute  nitric  acid  of  about  1'04  sp.  gr., 
and  also  a normal  soda  solution  (or  at  least  a soda  solution  whose  re- 
lation to  normal  sulphuric  acid  is  exactly  known). 

Fill  a Mohr’s  burette  with  the  nitric  acid,  measure  off  20  c.  c. ; 
color  with  tincture  of  cochineal  and  add  normal  solution  of  soda  from 
a second  burette  to  alkaline  reaction.  Repeat  the  experiment.  Sup- 
pose 20  c.  c.  of  the  acid  have  required  24  c.  c.  of  normal  soda  solution, 
add  to  every  20  volumes  of  the  acid  4 volumes  of  water.  For  the  pro- 
per way  of  effecting  the  dilution,  see  p.  493  (Preparation  of  Normal  Sul- 
phuric Acid).  After  diluting,  measure  off  20  c.  c.,  and  neutralize  with 
the  normal  solution  of  soda,  of  which  it  must  now  take  exactly  20  c.  c. 

It  will  be  well  to  verify  the  normal  nitric  acid  in  the  manner  direct- 
ed, p.  492. 

If  the  alkaline  earth  to  be  estimated  is  in  the  caustic  state,  weigh  off  a 
definite  quantity,  add  water,  then,  from  a burette  normal  nitric  acid, 
until  solution  is  effected,  and  the  fluid,  colored  with  cochineal,  appears 
orange;  now  add  soda  solution  until  the  color  just  changes  to  violet; 
deduct  the  soda  solution  added  from  the  acid,  and  calculate  by  the  pro- 
portion 

1000  (c.  c.)  : the  number  of  c.  c.  of  acid  used 

76*5  (eq.  baryta),  51*75  (eq.  strontia),  28  (eq.  lime)  or  20  (eq.  magnesia) 
: x (grm.  of  baryta,  strontia,  lime,  or  magnesia). 


504 


SPECIAL  PART. 


Should  there  be  a failure  the  first  time  in  determining  the  exact  point 
at  which  the  fluids  turn  violet,  add  another  c.  c.  of  the  acid,  and  then 
again  solution  of  soda  until  violet. 

In  the  case  of  carbonates  of  the  alkaline  earths,  heat  a weighed  quan- 
tity of  the  sample,  in  a flask,  with  water ; then  add,  from  the  burette 
small  portions  of  normal  nitric  acid.  When  solution  is  effected  and 
the  acid  is  consequently  in  excess,  add  tincture  of  cochineal,  then  nor- 
mal soda  solution,  till  only  a small  excess  of  acid  remains,  say  7}  or  1 
c.  c.  Heat  to  boiling,  shake  the  liquid,  and  continue  boiling  for  some 
minutes,  to  expel  the  carbonic  acid  completely  from  the  fluid  and  flask  ; 
finally  add  soda  until  just  violet.  1000  c.  c.  of  the  normal  acid  corre- 
spond to  98*5  grm.  carbonate  of  baryta,  73*75  grm.  carbonate  of  stron- 
tia,  50  grm.  carbonate  of  lime,  or  42  grm.  carbonate  of  magnesia. 

By  weighing  off  the  or  eq.  (H  — 1)  grm.  of  the  caustic  or  car- 
bonated alkaline  earths,  the  necessity  of  a calculation  of  the  results  is 
altogether  dispensed  with ; in  the  former  case,  the  number  of  c.  c.,  in 
the  latter  that  of  half  c.  c.  used  of  the  normal  acid,  expresses  the  per- 
centage required. 


5.  Chlorimetry. 

§ 211. 

The  “ chloride  of  lime,”  or  “ bleaching  powder  ” of  commerce,  con- 
tains hypochlorite  of  lime,  chloride  of  calcium,  and  hydrate  of  lime. 
The  two  latter  ingredients  are  for  the  most  part  combined  with  one 
another  to  basic  chloride  of  calcium.  In  freshly  prepared  and  perfectly 
normal  chloride  of  lime,  the  quantities  of  hypochlorite  of  lime  and 
chloride  of  calcium  present  stand  to  each  other  in  the  proportion  of 
their  equivalents.  When  such  chloride  of  lime  is  brought  into  contact 
with  dilute  sulphuric  acid,  the  wvhole  of  the  chlorine  it,  contains  is 
liberated  in  the  elementary  form,  in  accordance  with  the  following 
equation : — 

Ca  O,  Cl  O + Ca  Cl  + 2 (H  O,  S 03)=2  (Ca  O,  S 03)  + 2 H 0+2  Cl. 
On  keeping  chloride  of  lime,  however,  the  proportion  between  hypo- 
chlorite of  lime  and  chloride  of  calcium  gradually  changes — the  former 
decreases,  the  latter  increases.  Hence  from  this  cause  alone,  to  say 
nothing  of  original  difference,  the  commercial  article  is  not  of  uniform 
quality,  and  on  treatment  with  acid  gives  sometimes  more  and  sometimes 
less  chlorine. 

As  the  value  of  this  article  depends  entirely  upon  the  amount  of 
chlorine  set  free  on  treatment  with  acid,  chemists  have  devised  various 
simple  methods  of  determining  the  available  amount  of  chlorine  in  any 
given  sample.  These  methods  have  collectively  received  the  name  of 
Chlorimetry.  We  describe  a few  of  the  best. 

Preparation  of  the  Solution  of  Chloride  of  Lime. 

The  solution  is  prepared  alike  for  all  methods,  and  best  in  the  follow- 
ing manner  : — 

Weigh  off  10  grm.,  triturate  finely  with  a little  water,  add  gradually 
more  water,  pour  the  liquid  into  a litre  flask,  triturate  the  residue 
again  with  water,  and  rinse  the  contents  of  the  mortar  carefully  into 


212.] 


CHLORIMETRY. 


505 


the  flask ; fill  the  latter  to  the  mark,  shake  the  milky  fluid,  and  ex- 
amine it  at  once  in  that  state,  i.e.,  without  allowing  it  to  deposit ; and 
every  time,  before  measuring  off  a fresh  portion,  shake  again.  The  re- 
sults obtained  with  this  turbid  solution  are  much  more  constant  and  cor- 
rect than  when,  as  is  usually  recommended,  the  fluid  is  allowed  to  de- 
posit, and  the  experiment  is  made  with  the  supernatant  clear  portion 
alone.  The  truth  of  this  may  readily  be  proved  by  making  two  sepa- 
rate experiments,  one  with  the  decanted  clear  fluid,  and  the  other  with 
the  residuary  turbid  mixture.  Thus,  for  instance,  in  an  experiment 
made  in  my  own  laboratory,  the  decanted  clear  fluid  gave  2 2 ‘6  of 
chlorine,  the  residuary  mixture  25 ’0,  the  uniformly  mixed  turbid  solu- 
tion 24*5. 

1 c.  c.  of  the  solution  of  chloride  of  lime  so  prepared  corresponds  to 
0.01  grm.  chloride  of  lime. 

A.  Penot’s  Method  * 

§ 212. 

This  method  is  based  upon  the  conversion  of  arsenious  acid  into 
arsenic  acid ; the  conversion  is  effected  in  an  alkaline  solution.  Iodide 
of  potassium-starch  paper  is  employed  to  ascertain  the  exact  point  when 
the  reaction  is  completed. 

a.  Preparation  of  the  Iodide  of  Potassium- Starch  Paper. 

The  following  method  is  preferable  to  the  original  one  given  by  Pe- 
not  : — 

Stir  3 grm.  of  potato  starch  in  250  c.  c.  of  cold  water,  boil  with 
stirring,  add  a solution  of  1 grm.  iodide  of  potassium  and  1 grm. 
crystallized  carbonate  of  soda,  and  dilute  to  500  c.  c.  Moisten  strips 
of  fine  white  unsized  paper  with  this  fluid,  and  dry.  Keep  in  a closed 
bottle. 

b.  Preparation  of  the  Solution  of  Arsenious  Acid. 

Dissolve  4'436  grm.  of  pure  arsenious  acid  and  13  grm.  pure  crystal- 
lized carbonate  of  soda  in  600 — 700  c.  c.  water,  with  the  aid  of  heat, 
let  the  solution  cool,  and  then  dilute  to  1 litre.  Each  c.  c.  of  this  solu- 
tion contains  0 ’004436  grm.  arsenious  acid  which  corresponds  to  1 c.  c. 
chlorine  gas  of  0°  and  760  mm.  atmospheric  pressure.f 

As  arsenite  of  soda  in  alkaline  solution  is  liable,  when  exposed  to 
access  of  air,  to  be  gradually  converted  into  arseniate  of  soda,  Penot’s 
solution  should  be  kept  in  small  bottles  with  glass  stoppers,  filled  to  the 
top,  and  a fresh  bottle  used  for  every  new  series  of  experiments. 

* Bulletin  de  la  Societe  Industrielle  de  Mulhouse,  1852,  No.  118. — Dingler’s 
Polytech.  Journal,  127,  134. 

f Penot  gives  the  quantity  of  arsenious  acid  as  4 44  ; but  I have  corrected  this 
number  to  4 436,  in  accordance  with  the  now  received  equivalents  of  the  sub- 
stances and  specific  gravity  of  chlorine  gas — after  the  following  proportion : — 

70  92  (2  eq.  chlorine)  : 99  (1  eq.  AsOa) ::  3 17763  (weight  of  1 litre  of  chlorine  gas) 
: x ; X—  4’436,  i.e.  the  quantity  of  arsenious  acid  which  1 litre  of  chlorine  gas 
converts  into  arsenic  acid. 

This'solution  is  arranged  to  suit  the  foreign  method  of  designating  the  strength 
of  chloride  of  lime — viz. , in  chlorimetrical  degrees  (each  degree  represents  1 litre 
chlorine  gas  at  03  and  760  mm.  pressure  in  a kilogramme  of  the  substance).  This 


506 


SPECIAL  PART. 


According  to  Fr.  Mohr*  the  solution  keeps  unchanged,  if  the  arse- 
nious  acid  and  the  carbonate  of  soda  are  both  absolutely  free  from 
oxidizable  matters  (sulphide  of  arsenic,  sulphide  of  sodium,  sulphite  of 
soda). 

c.  T he  Process. 

Measure  off,  with  a pipette,  50  c.  c.  of  the  solution  of  chloride  of 
lime  prepared  according  to  the  directions  of  § 211,  transfer  to  a beaker, 
and  from  a 50  c.  c.  burette,  add,  slowly,  and  at  last  drop  by  drop,  the 
solution  of  arsenious  acid,  with  constant  stirring,  until  a drop  of  the 
mixture  produces  no  longer  a blue-colored  spot  on  the  iodized  paper; 
it  is  very  easy  to  hit  the  point  exactly,  as  the  gradually  increasing 
faintness  of  the  blue  spots  made  on  the  paper  by  the  fluid  dropped  on 
it,  indicates  the  approaching  termination  of  the  reaction,  and  warns  the 
operator  to  confine  the  further  addition  of  the  solution  of  arsenious 
acid  to  a single  drop  at  a time.  The  number  of  ^ c.  c.  used  indicates 
directly  the  number  of  chlorimetrical  degrees  (see  note),  as  the  follow- 
ing calculation  shows : suppose  you  have  used  40  c.  c.  of  solution  of 
arsenious  acid,  then  the  quantity  of  chloride  of  lime  used  in  the  experi- 
ment contains  40  c.  c.  of  chlorine  gas.  Now,  the  50  c.  c.  of  solution 
employed  correspond  to  0*5  grm.  of  chloride  of  lime;  therefore  0*5 
grm.  of  chloride  of  lime  contain  40  c.  c.  chlorine  gas,  therefore  1000 
grm.  contain  80000  c.  c.  = 80  litres.  This  method  gives  very  constant 
and  accurate  results,  and  appears  to  be  particularly  well  suited  for  use 
in  manufacturing  establishments  where  there  is  no  objection,  on  the 
score  of  danger,  to  the  employment  of  arsenious  acid.  (Expt.  No.  99.) 

B.  Otto’s  Method. 

8 213. 


The  principle  of  this  method  is  as  follows : — 

Two  eq.  protosulphate  of  iron,  when  brought  into  contact  with  chlo- 
rine, in  presence  of  water  and  free  sulphuric  acid,  give  1 eq.  ses- 
quisulphate  of  iron,  and  1 eq.  H Cl,  the  process  consuming  1 eq. 
chlorine. 

2 (Fe  0,S  03)  + S 03  + H0  + Cl.=Fe203,3  S 03-f  H Cl. 

2 eq.  crystallized  protosulphate  of  iron  : — 

2 (Fe  O,  S 03,  FI  O f6  aq.)  = 278 

correspond  to  35*46  of  chlorine,  or,  in  other  terms,  0*7839  grm.  crystal- 
lized protosulphate  of  iron  correspond  to  0*1  grm.  chlorine. 

The  protosulphate  of  iron  required  for  these  experiments  is  best  pre- 
pared as  follows : — 

Take  iron  nails,  free  from  rust,  and  dissolve  in  dilute  sulphuric  acid, 
applying  heat  in  the  last  stage  of  the  operation ; filter  the  solution, 

method  was  proposed  by  Gay-Lussac.  The  degrees  may  readily  be  converted 
into  per-cents,  and  rice  versa , thus : - A sample  of  chloride  of  lime  of  90°  contains 
90  x 347763=285  986  grm.  chlorine  in  1000  grm.  or  28 ‘59  in  100  ; and  a sample 
containing  34  2 per  cent,  chlorine,  is  of  107 ’G,  for  100  grm.  of  the  substance  con- 
tain 34  2 grm.  chlorine  . * . 1000  grm.  of  the  substance  contain  342  grm.  chlorine, 
but  342  grm.  chlorine  = ttiVAt  litres =107  '6  litres  . *.  1000  grm.  of  the  substance 
contain  107  6 litres  chlorine. 

* His  Lehrbuch  der  Titrirmethode,  2 Aufl.  S.  290. 


213.] 


CHLOItlMETRY. 


507 


still  hot,  into  about  twice  its  volume  of  spirit  of  wine.  The  precipitate 
consists  of 

Fe  O,  S 03+H  0 + 6 aq. 

Collect  upon  a filter,  wash  with  spirit  of  wine,  spread  upon  a sheet 
of  blotting  paper,  and  dry  in  the  air.  When  the  mass  smells  no  longer 
of  spirit  of  wine,  transfer  to  a bottle  and  keep  this  well  corked.  In- 
stead of  protosulphate  of  iron,  sulphate  of  protoxide  of  iron  and  ammo- 
nia (p.  93)  maybe  used.  OT  grm.  of  chlorine  oxidizes  1T055  grm.  of 
this /double  sulphate. 

The  Process. 

Dissolve  3T356  grm.  (4  X *07839  grm.)  of  the  precipitated  protosul- 
phate of  iron,  or  4*422  grm.  (4x  1*1055  grm.)  of  sulphate  of  protoxide  of 
iron  and  ammonia,  with  addition  of  a few  drops  of  dilute  sulphuric 
acid,  in  water,  to  200  c.  c. ; take  out,  with  a pipette,  50  c.  c.,  corre- 
sponding to  0*7839  grm.  protosulphate  of  iron,  or  1*1055  grm.  sulphate 
of  protoxide  of  iron  and  ammonia,  dilute  with  150 — 200  c.  c.  water, 
add  a sufficiency  of  pure  hydrochloric  acid,  and  run  in  from  a 50  c.  c. 
burette  the  freshly  shaken  solution  of  chloride  of  lime,  prepared  accord- 
ing to  § 211,  until  the  protoxide  of  iron  is  completely  converted  into 
sesquioxide.  To  know  the  exact  point  when  the  oxidation  is  completed, 
place  a number  of  drops  of  a solution  of  ferricyanide  of  potassium  on  a 
plate,  and,  when  the  operation  is  drawing  to  an  end,  apply  some  of  the 
mixture  with  a stirring-rod  to  one  of  the  drops  on  the  plate,  and  observe 
whether  it  produces  a blue  precipitate ; repeat  the  experiment  after 
every  fresh  addition  of  two  drops  of  the  solution  of  choride  of  lime. 
When  the  mixture  no  longer  produces  a blue  precipitate  in  the  solution 
of  ferricyanide  of  potassium  on  the  plate,  read  off  the  number  of  volumes 
used  of  the  solution  of  chloride  of  lime. 

The  amount  of  solution  of  chloride  of  lime  used  contained  0*1  grm. 
of  chlorine.  Suppose  40  c.  c.  have  been  used : as  every  c.  c.  corre- 
sponds to  0*01  grm.  of  chloride  o'f  lime,  the  percentage  by  weight  of 
available  chlorine  in  the  chloride  of  lime  is  found  by  the  following  pro- 
portion : — 

0*40  : 0*10  : : 100  : x\  cc=25 ; 

or,  by  dividing  1000  by  the  number  of  c.  c.  used  of  the  solution  of  chlo- 
ride of  lime. 

This  method  also  gives  very  satisfactory  results,  provided  always 
that  the  salts  of  protoxide  of  iron  are  perfectly  dry  and  free  from  ses- 
quioxide. 

Modification  of  the  preceding  Method. 

Instead  of  the  solution  of  protosu'lphate  of  iron,  a solution  of  proto- 
chloride of  iron,  prepared  by  dissolving  pianoforte  wire  in  hydrochloric 
acid  (according  to  p.  194,  aa ),  may  be  used  with  the  best  results.  If 
0*6316  of  pure  metallic  iron,  i.e .,  0*6335  of  fine  pianoforte  wfre  (which 
may  be  assumed  to  contain  99*7  per  cent,  of  iron),  are  dissolved  to  200 
c.  c.,  the  solution  so  prepared  contains  exactly  the  same  amount  of  iron 
as  the  solution  of  protosulphate  above  mentioned — that  is  to  say,  50 
c.  c.  of  it  correspond  to  0*1  grm.  chlorine.  But  as  it  is  inconvenient  to 
weigh  off  a definite  quantity  of  iron  wire,  the  following  course  may  be 
pursued  in  preference : weigh  off,  accurately,  about  0*15  grm.,  dissolve, 


508 


SPECIAL  PART. 


dilute  the  solution  to  about  200  c.  c.,  oxidize  the  iron  with  the  solution 
of  chloride  of  lime,  prepared  according  to  the  directions  of  § 211,  and 
calculate  the  chlorine  by  the  proportion 

56  : 35’46  : : the  quantity  of  iron  used  : x / 
the  x found  corresponds  to  the  chlorine  contained  in  the  amount  used  of 
the  solution  of  chloride  of  lime.  This  .calculation  may  be  dispensed  with 
by  the  application  of  the  following  formula,  in  which  the  carbon  in  the 
pianoforte  wire  is  taken  into  account : — 

Multiply  the  weight  of  the  pianoforte  wire  by  6313,  and  divide  the 
product  by  the  number  of  c.  c.  used  of  the  solution  of  chloride  of  lime  : 
the  result  expresses  the  percentage  of  chlorine  by  weight. 

This  method  gives  very  good  results.  I have  described  it  here  prin- 
cipally because  it  dispenses  altogether  with  the  use  of  standard  fluids.  It 
is  therefore  particularly  well  adapted  for  occasional  examinations  of 
samples  of  chloride  of  lime,  and  also  by  way  of  control.  (See  Expt. 
No.  99.) 

C.  Bunsen’s  Method. 

Pour  10  c.  c.  of  the  solution  of  chloride  of  lime,  prepared  according  to 
the  directions  of  § 211  (containing  0T  chloride  of  lime),  into  a beaker, 
and  add  about  6 c.  c.  of  the  solution  of  iodide  of  potassium,  prepared 
according  to  p.  314,  a (containing  0*6  KI) ; dilute  the  mixture  with  about 
100  c.  c.  water,  acidify  with  hydrochloric  acid,  and  determine  the  libera- 
ted iodine  as  directed  § 146.  As  1 eq.  iodine  corresponds  to  1 eq.  chlo- 
rine, the  calculation  is  easy.  This  method  gives  excellent  results.  (Com- 
pare Expt.  No.  99.) 

6.  Examination  of  Black  Oxide  of  Manganese. 

§214. 

The  native  black  oxide  of  manganese  (as  also  the  regenerated  artifi- 
cial product)  is  a mixture  of  binoxide  of  manganese  with  lower  oxides 
of  that  metal,  and  with  sesquioxide  of  iron,  clay,  &c.  ; it  also  invariably 
contains  moisture,  and  frequently  chemically  combined  water.  The  com- 
mercial value  of  the  article  depends  entirely  upon  the  amount  of  binoxide 
(or,  more  correctly  expressed,,  of  available  oxygen)  which  it  contains. 
By  “ available  oxygen  ” we  understand  the  excess  of  oxygen  contained 
in  a manganese,  over  the  1 eq.  combined  with  the  metal  to  protoxide ; 
upon  treating  the  ore  with  hydrochloric  acid,  an  amount  of  chlorine  is 
obtained  equivalent  to  this  excess  of  oxygen.  This  available  oxygen  is 
always  expressed  in  the  form  of  binoxide  of  manganese.  1 eq.  corre- 
sponds to  1 eq.  binoxide  of  manganese, ^ since  MnOa=MnO  + 0. 

I.  Drying  the  Sample. 

All  analyses  of  manganese  proceed  of  course  upon  the  supposition  that 
the  sample  operated  upon  is  a fair  average  specimen  of  the  ore.  A portion 
of  a tolerably  finely  powdered  average  sample  is  generally  sent  for  analysis 
to  the  chemist ; in  the  case  of  new  lodes,  however,  a number  of  samples, 
taken  from  different  parts  of  the  mine,  are  also  occasionally  sent.  If,  in 
the  latter  case,  the  average  composition  of  the  ore  is  to  be  ascertained,  and 


215.] 


VALUATION  OF  MANGANESE. 


509 

not  simply  that  of  the  several  samples,  the  following  course  must  be 
resorted  to  : crush  the  several  samples  of  the  ore  in  an  iron  mortar 
to  coarse  powder,  and  pass  the  whole  of  this  through  a rather  coarse  sieve. 
Mix  uniformly,  then  remove  a sufficiently  large  portion  of  the  coarse 
powder  with  a spoon,  reduce  it  to  powder  in  a steel  mortar,  passing  the 
whole  of  this  through  a fine  sieve.  Mix  the  powder  obtained  by  this 
second  process  of  pulverization  most  intimately;  take  about  8 — 10  grm. 
of  it,  and  triturate  this,  in  small  portions  at  a time,  in  an  agate  mortar,  to 
an  impalpable  powder.  Average  samples  are  generally  already  suffici- 
ently fine  to  require  only  the  last  operation. 

As  regards  the  temperature  at  which  the  powder  is  to  be  dried,  if  you 
desire  to  expel  the  whole  of  the  moisture  without  disturbing  any  of  the 
water  of  hydration,  the  temperature  adopted  must  be  120°  (this  is  the 
result  of  my  own  experiments,  see  Expt.  No.  100).  But,  as  there  ap- 
pears to  be  at  present  an  almost  universal  understanding  in  the  manga- 
nese trade,  to  limit  the  drying  temperature  to  100°,  the  fine  powder  is 
exposed,  in  a shallow  copper  or  brass  pan,  for  6 hours,  to  the  tempera- 
ture of  boiling  water,  in  a water-bath  (p.  37,  fig.  19). 

When  the  samples  have  been  dried,  they  are  introduced,  still  hot,  into 
glass  tubes  12- — 14  cm.  long,  and  8-— 10  mm.  wide,  sealed  at  one  end  ; 
these  tubes  are  then  corked  and  allowed  to  cool. 

In  laboratories  where  whole  series  of  analyses  of  different  ores  are  of 
frequent  occurrence,  it  is  advisable  to  number  the  drying-pans  and  glass 
tubes,  and  to  transfer  the  samples  always  from  the  pan  to  the  tube  of 
the  corresponding  number. 

II.  Determination  of  the  Binoxide  of  Manganese. 

§ 215. 

Of  the  many  methods  that  have  been  proposed  for  the  valuation  of 
manganese  ores,  I select  three  as  the  most  expeditious  and  accurate. 
The  first  is  more  particularly  adapted  for  technical  purposes. 

A.  Fresenius  and  Will?s  Method. 

a.  If  oxalic  acid  (or  an  oxalate)  is  brought  into  contact  with  binoxide 
of  manganese,  in  presence  of  water  and  excess  of  sulphuric  acid,  proto- 
sulphate of  manganese  is  formed,  and  carbonic  acid  evolved,  while  the 
oxygen,  which  we  may  assume  to  exist  in  the  binoxide  of  manganese  in 
combination  with  the  protoxide,  combines  with  the  elements  of  the  oxalic 
acid,  and  thus  converts  the  latter  into  carbonic  acid. 

Mn  02  + S03-f  C203— MnO,  S03+2  C 02. 

Each  equivalent  of  available  oxygen  or,  what  amounts  to  the  same, 
each  1 eq.  binoxide  of  manganese  = 43*5,  gives  2 eq.  carbonic  acid  = 44. 

b.  If  this  process  is  performed  in  a weighed  apparatus  from  which 
nothing  except  the  evolved  carbonic  acid  can  escape,  and  which,  at  the 
same  time,  permits  the  complete  expulsion  of  that  acid,  the  diminution 
of  weight  will  at  once  show  the  amount  of  carbonic  acid  which  has 
escaped,  and  consequently,  by  a very  simple  calculation,  the  quantity  of 
binoxide  contained  in  the  analyzed  manganese  ore.  As  44  parts  by 
weight  of  carbonic  acid  correspond  to  43’5  of  binoxide  of  manganese, 


SPECIAL  PART. 


510 


[§  215. 


the  carbonic  acid  found  need  simply  be  multiplied  by  43*5,  and  the  pro- 
duct divided  by  44,  or  the  carbonic  acid  may  be  multiplied  by 

— =0-9887, 

44  ’ 

to  find  the  corresponding  amount  of  binoxide  of  manganese. 

c.  But  even  this  calculation  may  be  avoided  by  simply  using  in  the 
operation  the  exact  weight  of  ore  which,  if  the  latter  consisted  of  pure 
binoxide,  would  give  100  parts  of  carbonic  acid. 

The  number  of  parts  evolved  of  carbonic  acid  expresses,  in  that  case, 
directly  the  number  of  parts  of  binoxide  contained  in  100  parts  of  the 
analyzed  ore.  It  results  from  b that  98*87  is  the  number  required. 
Suppose  the  experiment  is  made  with  0*9887  grm.  of  the  ore,  the  num- 
ber of  centigrammes  of  carbonic  acid  evolved  in  the  process  expresses 
directly  the  percentage  of  binoxide  contained  in  the  analyzed  manganese 
ore.  Now,  as  the  amount  of  carbonic  acid  evolved  from  0*9887  grm.  of 
manganese  would  be  rather  small  for  accurate  weighing,  it  is  advisable 
to  take  a multiple  of  this  weight,  and  to  divide  afterwards  the  number 
of  centigrammes  of  carbonic  acid  evolved  from  this  multiple  weight  by 
the  same  number  by  which  the  unit  has  been  multiplied.  The  multiple 
which  answers  the  purpose  best  for  superior  ores  is  the  triple,  — 2*966 ; 
for  inferior  ores,  I recommend  the  quadruple,  ±z  3*955,  or  the  quintuple, 
= 4*9435. 

The  analytical  process  is  performed  in 
the  apparatus  illustrated  in  fig.  100,  and 
which  has  been  described  already,  p.  289. 

The  flask  A should  hold,  up  to  the 
neck,  about  120  c. cl;  B about  100  c.  c. 
The  latter  is  half  filled  with  sulphuric 
acid  ; the  tube  a is  closed  at  b with  a 
little  wax  ball,  or  a very  small  piece  of 
caoutchouc  tubing,  with  a short  piece  of 
glass  rod  inserted  in  the  other  end. 

Place  2*966,  or  3*955,  or  4*9435  grm. — 
according  to  the  quality  of  the  ore — in 
a watch-glass,  and  tare  the  latter  most 
accurately  on  a delicate  balance ; then  re- 
move the  weights  from  the  watch-glass, 
and  replace  them  by  manganese  from  the 
tube,  very  cautiously,  with  the  aid  of  a 
gentle  tap  with  the  finger,  until  the  equi- 
librum  is  exactly  restored.  Transfer  the  weighed  sample,  with  the  aid 
of  a card,  to  the  flask  A , add  5 — 6 grm.  neutral  oxalate  of  soda,  or  about 
7*5  grm.  neutral  oxalate  of  potassa,  in  powder,  and  as  much  water  as 
will  fill  the  ftask  to  about  one-third.  Insert  the  cork  into  A,  and  tare  the 
apparatus  on  a strong  but  delicate  balance,  by  means  of  shot,  and  lastly 
tinfoil,  not  placed  directly  on  the  scale,  but  in  an  appropriate  vessel. 
The  tare  is  kept  under  a glass  bell.  Try  whether  the  apparatus  closes 
air-tight  (see  p.  289).  Then  make  some  sulphuric  acid  flow  from  B into 
A , by  applying  suction  to  d , by  means  of  a caoutchouc  tube.  The  evolu- 
tion of  carbonic  acid  commences  immediately  in  a steady  and  uniform 
manner.  When  it  begins  to  slacken,  cause  a fresh  portion  of  sulphuric 
acid  to  pass  into  A , and  repeat  this  until  the  manganese  ore  is  completely 


§ 215.] 


VALUATION  OF  MANGANESE. 


511 


decomposed,  which,  if  the  sample  has  been  very  finely  pulverized,  requires 
at  the  most  about  five  minutes.  The  complete  decomposition  of  the 
analyzed  ore  is  indicated,  on  the  one  hand,  by  the  cessation  of  the  dis- 
engagement of  carbonic  acid,  and  its  non-renewal  upon  the  influx  of  a 
fresh  portion  of  sulphuric  acid  into  A ; and,  on  the  other  hand,  by  the 
total  disappearance  of  every  trace  of  black  powder  from  the  bottom  of 
A* 

Now  cause  some  more  sulphuric  acid  to  pass  from  _Z?  into  A,  to  heat 
the  fluid  in  the  latter,  and  expel  the  last  traces  of  carbonic  acid  therein 
dissolved ; remove  the  wax  stopper,  or  india-rubber  tube,  from  b , and 
apply  gentle  suction  to  d until  the  air  drawn  out  tastes  no  longer  of 
carbonic  acid.  Let  the  apparatus  cool  completely  in  the  air,  and  place 
it  on  the  balance,  with  the  tare  on  the  other  scale,  and  restore  equilibri- 
um. The  number  of  centigramme  weights  added,  divided  by  3,  4,  or  5, 
according  to  the  multiple  of  09887  grm.  used,  expresses  the  percentage 
of  binoxide  contained  in  the  analyzed  ore. 

In  experiments  made  with  definite  quantities  of  the  ore,  weighing 
in  an  open  watch-glass  cannot  well  be  avoided,  and  the  dried  manganese 
is  thus  exposed  to  the  chance  of  a reabsorption  of  water  from  the  air, 
which  of  course  tends  to  interfere,  to  however  so  trifling  an  extent, 
with  the  accuracy  of  the  results.  In  very  precise  experiments,  there- 
fore, the  best  way  is  to  analyze  an  indeterminate  quantity  of  the  ore, 
and  to  calculate  the  percentage  as  shown  above.  For  this  purpose,  one 
of  the  little  corked  tubes,  filled  with  the  dry  pulverized  ore,  is  accu- 
rately weighed,  and  about  3 to  5 grm.  (according  to  the  quality  of  the 
ore)  are  transferred  to  the  flask  A.  By  now  reweighing  the  tube,  the 
exact  quantity  of  ore  in  the  flask  is  ascertained.  To  facilitate  this 
operation,  it  is  advisable  to  scratch  on  the  tube,  with  a file,  marks  indi- 
cating, approximately,  the  various  quantities  which  may  be  required  for 
the  analysis,  according  to  the  quality  of  the  ore. 

With  proper  skill  and  patience  on  the  part  of  the  operator,  a good 
balance  and  correct  weights,  this  method  gives  most  accurate  and  corre- 
sponding results,  differing  in  two  analyses  of  the  same  ore  barely  to  the 
extent  of  0*2  per  cent. 

If  the  results  of  two  assays  differ  by  more  than  02  per  cent.,  a third 
experiment  should  be  made.  In  laboratories  where  analyses  of  manga- 
nese ores  are  matters  of  frequent  occurrence,  it  will  be  found  conveni- 
ent to  use  an  aspirator  for  sucking  out  the  carbonic  acid.  In  the  case 
of  very  moist  air,  the  error  which  proceeds  from  the  fact  that  the  water 
in  the  air  drawn  through  the  apparatus  is  retained,  and  which  is  usu- 
ally quite  inconsiderable,  may  now  be  increased  to  an  important  extent. 
Under  such  circumstances,  connect  the  end  of  the  tube  b with  a chlo- 
ride of  calcium  tube  during  the  suction. 

Some  ores  of  manganese  contain  carbonates  of  the  alkaline  earths , 
which  of  course  necessitates  a modification  of  the  foregoing  process.  To 
ascertain  whether  carbonates  of  the  alkaline  earths  are  present,  boil  a 
sample  of  the  pulverized  ore  with  water,  and  add  nitric  acid.  If 
any  effervescence  takes  place,  the  process  is  modified  as  follows 
(Bohr,  j* ) : — 

* If  the  manganese  ore  has  been  pulverized  in  an  iron  mortar,  a few  black 
spots  (particles  of  iron  from  the  mortar)  will  often  remain  perceptible. 

f Zeitschrift  f.  analyt.  Chem.  1,  48. 


512 


SPECIAL  PART. 


After  the  weighed  portion  of  ore  has  been  introduced  into  the 
flask  A , treat  it  with  water,  so  that  the  flask  may  be  about  ^ full,  add 
a few  drops  of  dilute  sulphuric  acid  (1  part,  by  weight,  sulphuric  acid, 
to  5 parts  water)  and  warm  with  agitation,  preferably  in  a water  bath. 
After  some  time  dip  a rod  in  and  test  whether  the  fluid  possesses  a 
strongly  acid  reaction.  If  it  does  not,  add  more  sulphuric  acid.  As 
soon  as  the  whole  of  the  carbonates  are  decomposed  by  continued  heat- 
ing of  the  acidified  fluid,  completely  neutralize  the  excess  of  acid  with 
soda  solution  free  from  carbonic  acid,  allow  to  cool,  add  the  usual 
quantity  of  oxalate  of  soda,  and  proceed  as  above. 

If  you  have  no  soda  solution  free  from  carbonic  acid  at  hand,  you 
may  place  the  oxalate  of  soda  or  oxalic  acid  (about  3 grm.)  in  a small 
tube,  and  suspend  this  in  the  flask  A by  means  of  a thread  fastened  by 
the  cork.  When  the  apparatus  is  tared,  and  you  have  satisfied  yourself 
that  it  is  air-tight,  release  the  thread  and  proceed  as  above. 

B.  Bunsen’s  Method. 

Reduce  the  ore  to  the  very  finest  powder,  weigh  off  about  0*4  grm., 
introduce  this  into  the  small  flask  a,  illustrated  in  fig  59,  p.  308,  and 
pour  pure  fuming  hydrochloric  acid  over  it ; conduct  the  process  ex- 
actly as  in  the  analysis  of  chromates.  Boil  until  the  ore  is  completely 
dissolved  and  all  the  chlorine  expelled,  which  is  effected  in  a few  min- 
utes. Each  eq.  iodine  separated  corresponds  to  1 eq.  chlorine  evolved, 
and  accordingly  to  1 eq.  binoxide  of  manganese.  For  the  estimation  of 
the  separated  iodine,  the  method  § 146  may  be  employed.  Results 
most  accurate. 

C.  Estimation  of  the  Binoxide  of  Manganese  by  means  of  Iron. 

Dissolve,  in  a small  long-necked  flask,  placed  in  a slanting  position, 
about  1 grm.  pianoforte  wire,  accurately  weighed,  in  moderately  con- 
centrated pure  hydrochloric  acid ; weigh  off  about  0*6  grm.  of  the  sam- 
ple of  manganese  ore  in  a little  tube,  drop  this  into  the  flask,  with  its 
contents,  and  heat  cautiously  until  the  ore  is  dissolved.  1 eq.  binoxide 
of  manganese  converts  2 eq.  of  dissolved  iron  from  the  state  of  proto- 
to  that  of  sesquichloride.  When  complete  solution  has  taken  place, 
dilute  the  contents  of  the  flask  with  water,  allow  to  cool,  rinse  into  a 
beaker,  and  determine  the  iron  still  remaining  in  the  state  of  protochlo- 
ride with  chromate  of  potash  (p.  198).  Deduct  this  from  the  weight  of 
the  wire  employed  in  the  process  ; the  difference  expresses  the  quantity 
of  iron  which  has  been  converted  by  the  oxygen  of  the  manganese  from 
protochloride  to  sesquichloride.*  This  difference  multiplied  by  4-|g-5 
or  0*7768,  gives  the  amount  of  binoxide  in  the  analyzed  ore.  This  me- 
thod also,  if  carefully  executed,  gives  very  accurate  results.  If  you 
determine  the  excess  of  protochloride  of  iron  with  permanganate,  do 
not  forget  the  remarks  on  page  198,  note. 

The  main  reason  why  this  method  is  less  suitable  for  industrial  use 
than  the  first  lies  in  the  fact,  that  the  analyst  must  work  with  much 
smaller  quantities  of  substance.  Hence  to  obtain  results  equally  accurate 

* In  very  precise  experiments,  the  weight  of  the  iron  must  be  multiplied  by 
0*997,  since  pianoforte  wire  may  always  be  assumed  to  contain  about  0 003 
impurities. 


VALUATION  OF  MANGANESE. 


513 


gg  216,  217.] 

with  those  yielded  by  A,  far  greater  nicety  in  weighing  and  manipulat- 
ing is  required.  Instead  of  metallic  iron,  weighed  quantities  of  pure 
protosulphate  of  iron,  or  of  sulphate  of  protoxide  of  iron  and  ammonia, 
may  be  used. 

III.  Estimation  of  Moisture  in  Manganese. 

§216. 

In  the  purchase  and  sale  of  manganese,  a certain  proportion  of  moisture 
is  usually  assumed  to  be  present,  and  often  a percentage  is  fixed  within 
which  the  moisture  must  be  confined.  In  estimating  the  moisture  the 
same  temperature  should  be  employed,  at  which  the  drying  for  the  pur- 
pose of  determining  the  binoxide  is  effected  (§214,  I.). 

As  the  amount  of  moisture  in  an  ore  may  be  altered  by  the  operations 
of  crushing  and  pulverizing,  the  experiment  should  be  made  with  a sample 
of  the  mineral  which  has  not  yet  been  subjected  to  these  processes.  The 
drying  must  be  continued  until  no  further  diminution  of  weight  is  ob- 
served; at  100°,  this  takes  about  6 hours,  at  120°,  generally  only  1^ 
hours.  If  the  moisture  in  a manganese  ore  is  not  to  be  estimated  on  the 
spot,  but  in  the  laboratory,  a fair  average  sample  of  the  ore  should  be 
forwarded  to  the  chemist  in  a strong,  perfectly  dry,  and  well-corked 
bottle. 

IY.  Estimation  of  the  Amount  of  Hydrochloric  Acid  required 

FOR  THE  COMPLETE  DECOMPOSITION  OF  A MANGANESE. 


§ 217. 

Different  manganese  ores,  containing  the  same  amount  of  available 
oxygen,  or,  as  it  is  usually  expressed,  of  binoxide,  may  require  very  dif- 
ferent quantities  of  hydrochloric  acid  to  effect  their  decomposition  and 
solution,  so  as  to  give  an  amount  of  chlorine  corresponding  to  the  avail- 
able oxygen  in  them ; — thus,  an  ore  consisting  of  60  per  cent,  of  binoxide 
of  manganese  and  40  per  cent,  of  sand  and  clay,  requires  2 eq.  hydro- 
chloric acid  to  1 eq.  of  available  oxygen ; whereas  an  equally  rich  ore 
containing  lower  oxides  of  manganese,  sesquioxide  of  iron,  or  carbonate 
of  lime  requires  a much  larger  proportion  of  hydrochloric  acid. 

The  quantity  of  hydrochloric  acid  in  question  may  be  determined  by 
the  following  process  : — 

Determine  the  strength  of  10  c.  c.  of  a moderately  strong  hydrochloric 
acid  (of,  say,  TIG  sp.  gr.)  by  means  of  solution  of  sulphate  of  copper  and 
ammonia  (§  205).  Warm  10  c.  c.  of  the  same  acid  with  a weighed 
quantity  (about  1 grm.)  of  the  manganese,  in  a small  long-necked  flask, 
with  a glass  tube,  about  3 feet  long,  fitted  into  the  neck.  Fix  the  flask 
in  a position  that  the  tube  is  directed  obliquely  upwards,  and  then  gently 
heat  the  contents.  As  soon  as  the  manganese  is  decomposed,  aj^ply  a 
somewhat  stronger  heat  for  a short  time,  to  expel  the  chlorine  which  still 
remains  in  solution ; but  carefully  avoid  continuing  the  application  of 
heat  longer  than  is  absolutely  necessary,  as  it  is  of  importance  to  guard 
against  the  slightest  loss  of  hydrochloric  acid.  Let  the  flask  cool,  dilute 
the  contents  with  water,  and  determine  the  free  hydrochloric  acid  remain- 
ing by  solution  of  sulphate  of  copper  and  ammonia.  Deduct  the  quan- 
tity found  from  that  originally  added ; the  difference  expresses  the 

33 


514 


SPECIAL  PART. 


amount  of  hydrochloric  acid  required  to  effect  the  decomposition  of  the 
manganese  ore. 

7.  Analysis  of  Common  Salt. 

§ 218. 

I select  this  example  to  show  how  to  analyze,  with  accuracy  and 
tolerable  expedition,  salts  which,  with  a predominant  principal  ingredient, 
contain  small  quantities  of  other  substances. 

a.  Reduce  the  salt  by  trituration  to  a uniform  powder,  and  put  this 
into  a stoppered  bottle. 

b.  Weigh  off  10  grm.  of  the  powder,  and  dissolve  in  a beaker  by  diges- 
tion with  water ; filter  the  solution  into  a i-litre  flask,  and  thoroughly 
wash  the  small  residue  which  generally  remains.  Finally,  fill  the  flask 
with  water  up  to  the  mark,  and  shake  the  fluid. 

If  small  white  grains  of  sulphate  of  lime  are  left  on  dissolving  the  salt, 
reduce  them  to  powder  in  a mortar,  add  water,  let  the  mixture  digest  for 
some  time,  decant  the  clear  supernatant  fluid  on  to  a filter,  triturate  the 
undissolved  deposit  again,  add  water,  &c.,  and  repeat  the  operation  until 
complete  solution  is  effected. 

c.  Ignite  and  weigh  the  dried  insoluble  residue  of  b , and  subject  it  to 
a qualitative  examination,  more  especially  with  a view  to  ascertain  whether 
it  is  perfectly  free  from  sulphate  of  lime. 

d.  Of  the  solution  b,  measure  off  successively  the  following  quanti- 
ties : — 

For  e.  50  c.  c.  corresponding  to  1 grm.  of  common  salt. 

“ /.  150  c.  c.  “ “ 3 “ “ “ 

“ g.  150  c.  c.  “ “ 3 “ “ “ 

“ h.  50  c.  c.  “ “ 1 “ “ “ 

e.  Determine  in  the  50  c.  c.  measured  off,  the  chlorine  as  directed 
§ 141,  I.,  a or  b. 

f.  Determine  in  the  150  c.  c.  measured  off,  the  sulphuric  acid  as 
directed  § 132,  I.,  1. 

g.  Determine  in  the  150  c.  c.  measured  off,  the  lime  and  magnesia  as 
directed  p.  349,  29. 

h.  Mix  the  50  c.  c.  measured  off,  in  a platinum  dish,  with  about  ^ c.  c. 
of  pure  concentrated  sulphuric  acid,  and  proceed  as  directed  § 98,  1. 
The  neutral  residue  contains  the  sulphates  of  soda,  lime,  and  magnesia. 
Deduct  from  this  the  quantity  of  the  two  latter  substances  as  resulting 
from  g ; the  remainder  is  sulphate  of  soda. 

i.  Determine  in  another  weighed  portion  of  the  salt,  the  water  as 

directed  § 35 , a,  at  the  end. 

k.  Bromine  and  other  bodies,  of  which  only  very  minute  traces  are 
found  in  common  salt,  are  determined  by  the  methods  described  in 
Part  I. 

8.  Analysis  of  Gunpowder.* 

§219. 

Gunpowder,  as  is  well  known,  consists  of  nitre,  sulphur,  and  char- 

* As  regards  the  determination  of  the  sp.  gr.  of  gunpowder,  I refer  to  Heeren’a 
paper  on  the  subject,  in  Mittheilungen  des  Gewerbevereins  fur  Hannover,  1856, 
168— 178;  Polyt.  Centralbl.  1856,  1118. 


ANALYSIS  OF  GUNPOWDER. 


515 


§ 219.] 

coal,  and,  in  the  ordinary  condition,  invariably  contains  a small  quantity 
of  moisture.  The  analysis  is  frequently  confined  to  the  determination 
of  the  three  constituents  and  the  moisture,  but  often  the  examination  is 
extended  to  the  nature  of  the  charcoal,  and  the  carbon,  hydrogen,  oxy- 
gen, and  ash  therein  are  estimated. 

a . Determination  of  the  Moisture . 

Weigh  2 — 3 grm.  of  the  substance  (not  reduced  to  powder)  between 
two  well-fitting  watch-glasses,  and  dry  in  the  desiccator,  or  at  a gentle 
heat,  not  exceeding  GO0,  till  the  weight  remains  constant. 

h.  Determination  of  the  Nitre . 

Place  an  accurately  weighed  quantity  (about  5 grm.)  on  a filter,  mois- 
tened with  water  ; saturate  with  water,  and,  after  some  time,  repeatedly 
pour  small  quantities  of  hot  water  upon  it  until  the  nitrate  of  potassa  is 
completely  extracted.  Receive  the  first  filtrate  in  a small  weighed  pla- 
tinum dish,  the  washings  in  a beaker  or  small  flask.  Evaporate  the  con- 
tents of  the  platinum  dish  cautiously,  adding  the  washings  from  time  to 
time,  heat  the  residue  cautiously  to  incipient  fusion,  and  weigh  it.  * 

c.  Determination  of  the  Sulphur. 

Oxidize  2 — 3 grm.  of  the  powder  with  pure  concentrated  nitric  acid 
and  chlorate  of  potash,  the  latter  being  added  in  small  portions,  while 
the  fluid  is  maintained  in  gentle  ebullition.  If  the  operation  is  contin- 
ued long  enough,  it  usually  happens  that  hpth  the  charcoal  and  sulphur 
are  fully  oxidized,  and  a clear  solution  is  finally  obtained.  Evaporate 
with  excess  of  pure  hydrochloric  acid  on  a water-bath  to  dryness,  filter, 
if  undissolved  charcoal  should  render  it  necessary,  and  determine  the 
sulphuric  acid  after  § 132,  I.,  1. 

d.  Determination  of  the  Charcoal. 

Digest  a weighed  portion  of  the  powder  repeatedly  with  sulphide  of 
ammonium,  till  all  sulphur  is  dissolved,  collect  the  charcoal  on  a filter 
dried  at  100°,  wash  it  first  with  water  containing  sulphide  of  ammoni- 
um, then  with  pure  water,  dry  at  100°,  and  weigh. 

The  charcoal  so  obtained  must,  under  all  circumstances,  be  tested  for 
sulphur  by  the  method  given  under  c,  and  if  occasion  require,  the  sul- 
phur must  be  determined  in  an  aliquot  part.  The  charcoal  may  also  be 
examined  as  regards  its  behavior  to  potash  solution  (in  which  <£  red  char- 
coal”! is  partially  soluble)  and  an  aliquot  part  may  be  subjected  to  ele- 
mentary analysis  according  to  § 178.  For  this  latter  purpose  take  a 
portion  of  the  charcoal  dried  at  100°,  and  dry  at  190°  (Weltzien).  If 
the  charcoal,  on  this  second  drying,  suffers  a diminution  of  weight,  cal- 
culate the  latter  into  per-cents  of  the  gunpowder,  deduct  it  from  the 
charcoal,  and  add  it  to  the  moisture. 


* The  nitrate  of  potassa  may  also  be  estimated  in  an  expeditious  manner,  and 
with  sufficient  accuracy  for  technical  purposes,  by  means  of  a hydrometer,  which 
is  constructed  to  indicate  the  percentage  of  this  ingredient  when  floated  in  water 
containing  a certain  proportion  of  gunpowder  in  solution.  A method  based  upon 
the  same  principle,  proposed  by  Uchatius.  is  given  in  the  Wiener  akad.  Ber.  X, 
748 ; also  Ann.  d.  Chem.  und  Pharm.  88,  395. 
f Incompletely  carbonized  wood. 


516 


SPECIAL  PART. 


9.  Analysis  of  Native  and,  more  particularly,  of  Mixed  Silicates.* 


§ 220. 

The  analysis  of  silicates  which  are  completely  decomposed  by  acids 
has  been  described  in  § 140,  II.,  a ; and  that  of  silicates  which  are  not 
decomposed  by  acids,  in  § 140,  II.,  b.  I have  therefore  here  only  to  add 
a few  remarks  respecting  the  examination  of  mixed  silicates,  i.e .,  of  such 
as  are  composed  of  silicates  of  the  two  classes  (phonolites,  clay-slates, 
basalts,  meteoric  stones,  &c.). 

After  the  silicate  has  been  very  finely  pulverized  and  dried  at  100° 
it  is  usually  treated  for  some  time,  at  a gentle  heat,  with  moderately 
concentrated  hydrochloric  acid,  evaporated  to  dryness  on  the  water-bath, 
the  residue  moistened  with  hydrochloric  acid,  water  added,  and  the  solu- 
tion filtered  ; it  is  often  preferable,  however,  to  digest  the  powder  with 
dilute  hydrochloric  acid  (of  about  15  per  cent.)  for  some  days  at  a gen- 
tle heat,  and  then  at  once  filter  the  solution.  Which  of  the  two  ways 
it  is.  advisable  to  adopt,  and  indeed  whether  the  method  here  described 
(which  was  first  employed  by  Chr.  Gmelin  in  the  analysis  of  phonolites), 
may  be  resorted  to,  depends  upon  the  nature  of  the  mixed  minerals. 
The  more  readily  decomposable  the  one  of  the  constituent  parts  of  the 
mixture  is,  and  the  less  readily  decomposable  the  other,  the  more  con- 
stant the  proportion  between  the  undissolved  and  the  dissolved  part  is 
found  to  remain  in  different  experiments  ; in  other  words,  the  less  the 
undissolved  part  is  affected  by  further  treatment  with  hydrochloric  acid, 
the  more  safely  may  this  method  of  decomposition  be  resorted  to. 

The  process  gives  : — 

a.  A hydrochloric  acid  solution , containing,  besides  a little  silicic 
acid,  the  bases  of  the  decomposed  silicate  in  the  form  of  metallic  chlo- 
rides, which  are  separated  and  determined  by  the  proper  methods. 

b.  An  insoluble  residue , which  contains,  besides  the  undeconrposed 
silicate,  the  separated  silicic  acid  of  the  decomposed  silicate. 

After  the  latter  has  been  well  washed  with  water,  to  which  a few 
drops  of  hydrochloric  acid  have  been  added,  transfer  it,  still  moist,  in 
small  portions  at  a time,  to  a boiling  solution  of  carbonate  of  soda  (free 
from  silicic  acid)  contained  in  a platinum  dish ; boil  for  some  time,  and 
filter  off  each  time,  still  very  hot,  through  a weighed  filter.  Finally, 
rinse  the  last  particles  of  the  residue  which  still  adhere  to  the  filter  com- 
pletely into  the  dish,  and  proceed  as  before.  Should  this  operation  not 
fully  succeed,  dry  and  incinerate  the  filter,  transfer  the  ash  to  the  pla- 
tinum dish,  and  boil  repeatedly  with  the  solution  of  carbonate  of  soda 
till  a few  drops  of  the  fluid  finally  passing  through  the  filter  remain 
clear  on  warming  with  excess  of  chloride  of  ammonium.  Wash  the 
residue,  first  with  hot  water,  then — to  insure  the  removal  of  every  trace 
of  carbonate  of  soda  which  may  still  adhere  to  it — with  water  slightly 
acidified  with  hydrochloric  acid,  and  finally  again  with  pure  water. 
Collect  the  washings  in  a separate  vessel  (H.  Rose). 

Acidify  the  alkaline  filtrate  with  hydrochloric  acid,  and  determine  in 
it  the  silicic  acid  which  belongs  to  the  silicate  decomposed  by  hydro- 
chloric acid,  as  directed  § 140,  II.,  a.  Dry  the  undissolved  silicate  at 

* Comp.  Qua!  Anal.  §§  205-208.  The  quantitative  analysis  must  always  be 
preceded  by  a minute  and  comprehensive  qualitative  analysis. 


§ 220.] 


ANALYSIS  OF  NATIVE  SILICATES. 


517 


100°,  and  weigh.  The  difference  gives  the  quantity  of  the  dissolved 
silicate.  Treat  the  undissolved  silicate  exactly  as  directed  § 140, 
II.,  b. 

Silicates  dried  at  100°  occasionally  contain  water.  This  is  determined 
by  taking  a weighed  portion  of  the  mixed  silicate  dried  at  100°  and 
igniting  in  a platinum  crucible,  or — in  presence  of  carbon  or  protoxide 
of  iron — in  a tube,  through  which  a stream  of  dry  air  is  drawn,  the 
moisture  expelled  from  the  substance  being  retained  by  a weighed  chlo- 
ride of  calcium  tube.  To  ascertain  whether  the  water  thus  expelled 
proceeds  from  the  silicate  decomposable  by  hydrochloric  acid,  or  from 
that  which  hydrochloric  acid  fails  to  decompose,  a sample  of  the  latter, 
dried  at  100°,  is  also  ignited  in  the  same  manner.  Suppose,  for  instance, 
the  mixed  silicate  under  examination  consists  of  50  per  ceut.  of  silicate 
decomposed  by  hydrochloric  acid,  and  50  per  cent,  of  silicate  which 
hydrochloric  acid  fails  to  decompose ; and  that  the  latter  contains  47 
parts  of  anhydrous  substance,  and  3 parts  of  water ; the  determination 
of  the  water  would  give,  for  the  mixed  silicate  3 per  cent.,  for  the  por- 
tion not  decomposed  by  hydrochloric  acid  6 per  cent.  Now,  as  3 bears 
the  same  proportion  to  6 as  the  undecomposed  silicate  (50  per  cent.) 
bears  to  the  mixed  silicate  (100  per  cent.),  it  is  clear  that  the  silicate 
decomposed  by  hydrochloric  acid  gives  no  water  upon  ignition. 

If  the  escaping  aqueous  vapors  manifest  acid  reaction,  owing  to  dis- 
engagement of  hydrochloric  acid  or  Jluoride  of  silicon,  mix  the  substance 
with  6 parts  of  finely  triturated  recently  ignited  oxide  of  lead  in  a sm^ll 
retort,  weigh,  ignite,  and  weigh  again.  If  the  water  passing  over  still 
manifests  acid  reaction,  connect  the  retort  with  a small  receiver  contain- 
ing water,  and  determine  the  hydro fluosilicic  acid  in  the  latter,  after  the 
termination  of  the  process.  According  to  Sainte-Claire  Deville  and 
Fouque,*  by  properly  conducting  the  ignition  the  water  may  usually  be 
expelled  free  from  combinations  of  fluorine,  since  the  latter  require  a 
far  higher  temperature  for  expulsion  than  the  former  requires.  After 
the  water  has  been  driven  off  the  fluorine  is  then  expelled  bv  stronger 
ignition,  either  as  alkaline  metallic  fluoride  or  as  fluoride  of  silicon. 

The  undecomposed  part  of  a mixed  silicate  occasionally  contains  car- 
bonaceous organic  matter , in  which  case  it  is  the  safest  way  to  treat  an 
aliquot  part  of  it  in  a current  of  oxygen  gas,  and  weigh  the  carbonic 
acid  produced  (§  178).  According  to  Delesse,  traces  of  nitrogen  are 
almost  invariably  present  in  the  organic  matter  contained  in  silicates.  • 

Silicates  often  contain  admixtures  of  other  minerals  (magnetite,  pyrites, 
apatite,  carbonate  of  lime,  &c.)  which  may  sometimes  be  detected  by  the 
naked  eye  or  with  the  aid  of  a magnifying  glass.  It  would  be  rather  a 
difficult  undertaking  to  devise  a generally  applicable  method  for  cases 
of  this  description ; I therefore  simply  remark  that  it  is  occasionally 
found  advantageous  to  treat  the  substance  first  with  acetic  acid,  before 
subjecting  it  to  the  action  of  hydrochloric  acid  ; this  will  more  especially 
effect,  without  the  least  difficulty,  the  separation  of  the  carbonates  of  the 
alkaline  earths.  As  examples  of  complete  examinations  of  this  kind  I 
may  cite  some  analyses  by  Dollfuss  and  Neubauer,!  which  were  made 
in  my  laboratory. 

If  sulphides  are  present,  determine  the  sulphur  by  one  of  the  methods 


* Compt.  rend.  38,  317;  Journ.  f.  prakt.  Chem.  62,  78. 
f Journ.  f.  prakt.  Chem.  65,  199. 


518 


SPECIAL  PART. 


[§  220. 


given  § 148,  II.,  A.*  As  regards  the  methods  in  the  wet  way,  it  must  be 
borne  in  mind,  that  when  baryta,  strontia,  or  lead  is  present,  a portion 
of  the  sulphuric  acid  produced  remains  in  the  insoluble  residue ; on  fusion 
with  alkaline  carbonate  and  nitrate  this  is  not  the  case.  If,  besides 
sulphide,  a sulphate  is  present,  determine  the  sulphuric  acid  of  the  latter, 
by  boiling  a separate  portion  of  the  substance  with  a solution  of  carbonate 
of  potash  or  soda  for  a long  time,  filtering,  acidifying  the  filtrate,  and 
precipitating  with  chloride  of  barium.  The  sulphuric  acid  thus  obtained 
is  deducted  from  the  quantity  obtained  after  treatment  with  oxidizing 
agents,  and  the  remainder  corresponds  with  the  sulphur  in  the  sulphide. 

The  protoxide  of  iron  may  be  conveniently  determined  by  Cooke’s 
process  (p.  369). 

If  silicates  contain  small  quantities  of  titanic  acid , as  is  very  frequently 
the  case,  care  must  be  taken  not  to  overlook  this  admixture.  If  the  silicic 
acid  has  been  separated  by  evaporation  with  hydrochloric  acid— whether 
preceded  or  not.  by  decomposition  with  carbonated  alkali — and  the  eva- 
poration has  been  effected  on  the  water-bath,  and  the  dry  mass  has  been 
treated  with  a sufficient  quantity  of  hydrochloric  acid,  the  titanic  acid, 
or  at  least  by  far  the  greater  part  of  it,  is  found  in  the  hydrochloric  acid 
solution. 

The  separated  silica  may  be  tested  for  titanic  acid,  as  follows  : — Treat 
in  a platinum  dish  with  hydrofluoric  acid  and  a little  sulphuric  acid, 
evaporate,  fuse  the  residue  with  bisulphate  of  potash,  dissolve  in  cold 
water,  filter  if  necessary,  and  separate  the  titanic  acid  from  the  sulphuric 
acid  solution  by  the  method  given  § 107. 

As  regards  the  titanic  acid  contained  in  the  hydrochloric  acid  solution 
filtered  from  the  silicic  acid,  it  is  precipitated  with  the  sesquioxide  of 
iron  and  alumina,  when  ammonia  is  added  (§161,3).  In  this  precipitate 
it  may  be  determined  either  (a)  by  igniting  the  precipitate  in  hydrogen, 
extracting  the  reduced  iron  by  digestion  with  dilute  hydrochloric  acid, 
fusing  the  residue  with  bisulphate  of  potash,  taking  up  with  cold  water, 
and  precipitating  the  titanic  acid  by  boiling  (§  107)  or  ( b ) by  fusing  the 
precipitate  at  once  with  bisulphate  of  potash,  dissolving  in  cold  water, 
neutralizing  the  solution  as  nearly  as  possible  with  carbonate  of  soda, 
diluting  with  water,  so  that  not  more  than  0*1  grm.  of  the  oxides  may 
be  contained  in  50  c.  c.,  adding  to  the  cold  solution  hyposulphite  of  soda 
in  slight  excess,  waiting  till  the  fluid,  which  was  at  first  violet,,  has 
become  quite  colorless,  and  consequently  the  whole  of  the  sesquioxide 
of  iron  is  reduced,  boiling  till  sulphurous  acid  ceases  to  be  disengaged, 
filtering,  washing  the  precipitate  with  boiling  water,  drying,  gently 
igniting  in  a covered  porcelain  crucible,  to  expel  sulphur,  then  taking 
the  lid  off  and  increasing  the  heat;  we  thus  obtain  the  alumina 
(Chancel))  and  the  titanic  acid  (A.  StromeyerJ)  together,  free  from 
sesquioxide  of  iron ; they  are  separated  by  the  method  above  given. 

10.  Analysis  of  Limestones,  Dolomites,  Marls,  <fcc. 

As  the  minerals  containing  carbonate  of  lime  and  carbonate  of  mag- 
nesia play  a very  important  part  in  manufactures  and  agriculture,  the 


* The  methods  in  the  wet  way  would  as  a rule  be  preferable, 
f Compt.  rend.  46,  987 ; Anna!  d.  Chem.  u.  Pharm.  108,  237. 
\ AnnaL  d.  Chem.  u.  Pharm.  113,  127. 


§ 221.]  ANALYSIS  OF  LIMESTONES,  DOLOMITES,  MARJ*S,  ETC.  519 

chemist  is  often  called  upon  to  analyze  them.  The  analytical  process 
differs  according  to  the  different  object  in  view.  For  technical  purposes, 
it  is  sufficient  to  deterinine  the  principal  constituents ; the  geologist  takes 
an  interest  also  in  the  matter  present  in  smaller  proportions  ; whilst  the 
agricultural  chemist  seeks  a knowledge  not  only  of  the  constituents,  but 
also,  of  the  state  of  solubility,  in  different  menstrua,  in  which  they  are 
severally  present. 

I will  give,  in  the  first  place,  a process  for  effecting  a complete  and 
accurate  analysis  ; and,  in  the  second  place,  the  volumetric  methods  by 
which  the  carbonate  of  lime  (and  the  carbonate  of  magnesia)  may  be 
determined.  An  accurate  qualitative  examination  should  always  pre- 
cede the  quantitative  analysis. 

A.  Method  of  Effecting  the  Complete  Analysis. 

§ 221. 

a.  Reduce  a large  piece  of  the  mineral  to  powder,  mix  this  uniformly, 
and  dry  at  100°. 

b.  Treat  about  2 grm.,  in  a covered  beaker,  with  dilute  hydrochloric 
acid  in  excess,  evaporate  to  dryness  in  a platinum  or  porcelain  dish, 
moisten  the  residue  with  hydrochloric  acid,  heat  with  water,  filter  on  a 
dried  and  weighed  filter,  wash  the  insoluble  residue,  dry  at  100°,  and 
weigh.  It  generally  consists  of  separated  silicic  acid , clay , and  sand  : 
but  it  often  contains  also  humus-like  matter.  Opportunity  will  be  afforded 
in  y for  examining  this  residue. 

c.  Mix  the  hydrochloric  acid  solution  with  chlorine  water,  then  with 
ammonia  in  slight  excess,  and  let  the  mixture  stand  at  rest  for  some 
time,  in  a covered  vessel,  at  a gentle  heat.  Filter  off  the  precipitate, 
which  contains — besides  the  hydrates  of  sesquioxide  of  iron,  sesquioxide 
of  manganese,  and  alumina — the  phosphoric  acid  which  the  analyzed 
compound  may  contain,  and,  moreover,  invariably  traces  of  lime  and 
magnesia ; wash  slightly,  and  redissolve  in  hydrochloric  acid  ; heat  the 
solution,  add  chlorine  water,  and  then  precipitate  again  with  ammonia ; 
filter  off  the  precipitate,  wash,  dry,  ignite,  and  Aveigh. 

For  the  estimation  of  the  several  components  of  the  precipitates,  viz., 
sesquioxide  of  iron , proto  sesquioxide  of  manganese , alumina , and  phos- 
phoric acid,  opportunity  will  be  afforded  in  g. 

d.  Unite  the  fluids  filtered  from  the  first  and  second  precipitates  pro- 
duced by  ammonia,  and  determine  the  lime  and  magnesia  as  directed  § 

154,  6 (29). _ 

e.  If  the  limestone  dried  at  100°  still  gives  water  upon  ignition,  this 
is  estimated  best  as  directed  § 36. 

f.  If  the  limestone  contains  no  other  volatile  constituents  besides 
water  and  carbonic  acid,  ignite  with  fused  borax  (p.  288,  c),  and  sub- 
tract from  the  loss  of  weight  suffered,  the  water  found  in  e ; the  differ- 
ence is  the  carbonic  acid.  If  this  method  is  inapplicable,  determine  the 
carbonic  acid  as  directed  p.  290,  bb,  or  291,  cc,  or  as  on  p.  293,  e. 

g.  To  effect  the  estimation  of  the  constituents  present  in  smaller  pro- 
portion, as  well  as  the  analysis  of  the  residue  insoluble  in  hydrochloric 
acid,  and  of  the  precipitate  produced  by  ammonia,  dissolve  20 — 50  grm. 
of  the  mineral  in  hydrochloric  acid.  As  the  evaporation  to  dryness  of 
large  quantities  of  fluid  is  always  a tedious  operation,  gently  heat  the 


520 


SPECIAL  PART. 


solution  for  some  time,  to  expel  the  carbonic  acid  ; then  filter  through  a 
weighed  filter  into  a litre  flask,  wash  the  residue,  dry,  and  weigh  it. 
(The  weight  will  not  quite  agree  with  that  of  the  residue  in  b,  as  the 
latter  contains  also  that  part  of  the  silicic  acid  which  here  still  remains 
in  solution.) 

a.  Analysis  of  the  insoluble  Residue. 

aa.  Treat  a portion  with  boiling  solution  of  pure  carbonate  of  soda 
(§  220,  5),  and  separate  the  silicic  acid  from  the  solution  (§  140,  II.,  a) ; 
this  process  gives  the  quantity  of  that  portion  of  the  silicic  acid  con- 
tained in  the  residue,  which  is  soluble  in  alkalies. 

bb.  Treat  another  portion,  by  the  usual  process  for  silicates  (§  140, 
II.,  b),  and  deduct  from  the  silicic  acid  found,  the  amount  obtained  in  aa. 

cc.  If  the  residue  contains  organic  matter  (humus),  determine,  in  a 
portion,  the  carbon  by  the  method  of  ultimate  analysis  (p.  430,  b). 
Petzholdt,*  who  determined  by  this  method  the  coloring  organic  mat- 
ter of  several  dolomites,  assumes  that  58  parts  of  carbon  correspond  to 
100  parts  of  organic  substance  (humic  acid). 

dd.  If  the  residue  contains  pyrites ,f  fuse  another  portion  of  it  with 
carbonate  of  soda  and  nitrate  of  potassa ; macerate  in  water,  add  hydro- 
chloric acid,  evaporate  to  dryness,  moisten  with  hydrochloric  acid,  gently 
heat  with  water,  filter,  determine  the  sulphuric  acid  in  the  filtrate,  and 
calculate  from  the  result  the  amount  of  pyrites  present.^ 

/3.  Analysis  of  the  Hydrochloric  Acid  Solution. 

Make  the  solution  up  to  1 litre. 

aa.  For  the  determination  of  the  silicic  acid  that  has  passed  into  solu- 
tion, and  of  the  baryta,  strontia,  alumina , manganese , iron,  and  phos- 
phoric acid , evaporate  500  c.  c.,  and  dry  the  residue  at  100 — 110°.  Treat 
the  dry  mass,  in  order  to  separate  silicic  acid,  &c.  (precipitate  I.),  with 
hydrochloric  acid  and  water,  boil  the  solution  with  nitric  acid,  add  am- 
monia, boil  till  the  excess  of  ammonia  has  escaped,  filter,  wash  slightly, 
dissolve  on  the  filter  with  hydrochloric  acid,  reprecipitate  in  the  same 
manner  with  ammonia,  and  filter  off*  precipitate  II.,  which  contains 
sesquioxide  of  iron,  &c.  Digest  the  united  filtrates  in  a nearly  filled 
and  closed  flask  with  sulphide  of  ammonium  in  a slightly  warm  place 
for  24  hours,  then  filter  off  precipitate  III.  This  consists  principally  of 
sulphide  of  manganese  ; it  is  to  be  washed  with  water  containing  sul- 
phide of  ammonium.  Precipitate  the  filtrate  with  carbonate  of  ammo- 
nia and  ammonia,  allow  to  stand  24  hours,  and  then  filter  off  precipitate 
IV.,  which  consists  for  the  most  part  of  carbonate  of  lime,  and  is  to  be 
washed  with  water  containing  ammonia.  Evaporate  the  filtrate  in  a 
porcelain  dish  to  dryness,  project  the  residue,  little  by  little,  into  a red 
hot  platinum  dish,  drive  off  the  ammonia  salts,  moisten  the  residue  with 
hydrochloric  acid,  dissolve  it  in  water,  and  boil,  with  addition  of  pure 
milk  of  lime,  to  strongly  alkaline  reaction.  Filter  off  precipitate  V., 

* Journ.  f.  prakt.  Chem.  63,  194. 

f Compare  Petzholdt,  loc  cit.  ; Ebelmen  (Compt.  rend.  33,  681) ; Deville 
(Compt  rend.  37,  1001;  Journ.  f.  prakt.  Chem.  62,  81);  Roth  (Journ.  f.  prakt. 
Chem.  58,  84). 

f If  the  residue  contains  sulphate  of  baryta  or  strontia,  these  compounds  are 
formed  again  upon  evaporating  the  soaked  mass  with  hydrochloric  acid  ; they 
remain  accordingly  on  the  filter,  whilst  the  sulphuric  acid  formed  by  the  sulphur 
of  the  pyrites  passes  into  the  filtrate. 


§221.] 


ANALYSIS  OF  LIMESTONES,  DOLOMITES,  MARLS,  ETC. 


521 


which  is  composed  of  magnesia  and  the  excess  of  lime,  wash  it,  precipi- 
tate the  filtrate  with  carbonate  of  ammonia  and  ammonia,  and,  after 
long  standing,  filter  off'  precipitate  VI.,  which  is  to  be  washed  with 
water  containing  ammonia. 

Precipitate  1 . consists  principally  of  silicic  acid.  It  may  also  contain 
sulphates  of  baryta  and  strontia.  Treat  it  in  a platinum  dish  with 
hydrofluoric  acid  and  a little  sulphuric  acid,  evaporate  to  dryness,  and, 
if  necessary,  repeat  this  operation.  Should  a residue  remain,  fuse  it 
with  a small  quantity  of  carbonate  of  soda,  treat  with  water,  filter,  wash, 
dissolve  in  hydrochloric  acid,  and  precipitate  the  solution  with  sulphuric 
acid.  When  the  precipitate  has  settled  filter  it  from  solution  a,  and 
wash.  Stop  up  the  tube  of  the  funnel,  and  fill  the  latter  with  solution 
of  carbonate  of  ammonia,  allow  to  stand  1 2 hours,  open  the  funnel  tube, 
wash  the  residue  first  with  water,  then  with  hydrochloric  acid  (solution 
b),  finally  again  with  water,  and  then  weigh  the  pure  residual  sulphate 
of  baryta.  Mix  the  united  solutions  a and  b with  carbonate  of  am- 
monia and  ammonia,  allow  to  stand  some  time  ; if  a precipitate  forms 
(which  may  contain  carbonate  of  strontia)  filter  it  off,  dry,  and  add  to 
precipitate  IV. 

Precipitate  II.  consists  principally  of  sesqnioxide  of  iron  ; it  contains 
also  the  alumina,  and,  provided  there  is  enough  iron,  the  whole  of  the 
phosphoric  acid.  Dissolve  in  hydrochloric  acid,  add  pure  tartaric  acid, 
and  then  ammonia.  Having  fully  convinced  yourself  that  no  precipitate 
is  formed,  precipitate  the  iron  with  sulphide  of  ammonium  in  a small 
flask,  which  must  be  nearly  filled  and  closed,  allow  to  stand  till  the  fluid 
appears  of  a pure  yellow  color,  filter,  wash  with  water  containing  sul- 
phide of  ammonium,  and  determine  the  iron  after  § 113,  2.  To  the  fil- 
trate add  a little  pure  carbonate  of  soda  and  pure  nitrate  of  potassa, 
evaporate  to  dryness,  and  ignite  till  the  residue  is  white.  Add  water 
and  hydrochloric  acid  till  the  whole  is  dissolved,*  and  precipitate  the 
clear  fluid  with  ammonia.  If  a precipitate  forms  (alumina  or  phosphate 
of  alumina,  or  a mixture  of  both),  filter  it  off,  and  weigh.  Mix  the  fil- 
trate with  a little  sulphate  of  magnesia.  If  another  precipitate  forms, 
this  time  consisting  of  ammonio -phosphate  of  magnesia  (which  is  to  be 
determined  after  § 134,  I.,  b.  a)  the  alumina  precipitate  may  be  calcu- 
lated as  phosphate  of  alumina  (Al2  03,  P 05).  If,  on  the  contrary,  no 
precipitate  is  formed,  the  phosphoric  acid  must  be  determined  in  the 
alumina  precipitate  as  directed  § 134,  I.,  b , /?. 

Precipitate  III  consists  principally  of  sulphide  of  manganese.  It 
may  also  contain  traces  of  sulphides  of  nickel,  cobalt,  and  zinc,  car- 
bonate of  lime,  &c.  Treat  with  moderately  dilute  acetic  acid,  heat  the 
filtrate,  to  remove  any  carbonic  acid,  add  ammonia,  precipitate  with  sul- 
phide of  ammonium,  allow  to  stand  24  hours,  and  determine  the  man- 
ganese as  protosulphide  (§  109,  2).  If  any  residue  was  left  insoluble  in 
acetic  acid,  test  it  for  the  above-mentioned  metals.  The  fluid  filtered 
from  the  pure  sulphide  of  manganese  is  to  be  mixed  with  carbonate  of 
ammonia.  If  a precipitate  forms  it  is  to  be  treated  with  precipitate  IV. 

Precipitates  IV.  V.  VI  The  united  mass  of  these  precipitates,  to- 
gether with  the  small  portions  of  alkaline  earthy  carbonates  obtained 
during  the  treatment  of  precipitates  I.  and  III.  contain  the  whole  of  the 


* I may  remind  the  operator  that  the  residue,  which  contains  nitric  acid,  can- 
not be  heated  with  hydrochloric  acid  in  a platinum  dish. 


522 


SPECIAL  PART. 


strontia  and  the  whole  of  the  baryta  which  originally  passed  into  the 
hydrochloric  acid  solution.  Ignite  the  dried  precipitate  (if  necessary  in 
portions)  in  a platinum  crucible,  most  intensely  over  the  gas  blowpipe. 
By  this  means  any  carbonates  of  baryta  and  strontia  are  converted  into 
the  caustic  state,  and  a part,  at  all  events,  of  the  carbonate  of  lime  into 
lime  (Engelbach  *).  Boil  the  residue  5 or  6 times  with  small  portions 
of  water,  pouring  off  the  solution  through  a filter  ; neutralize  the  solu- 
tion with  hydrochloric  acid,  evaporate  to  dryness,  and  test  a minute 
portion  with  the  spectroscope — this  minute  portion  is  afterwards  added 
to  the  rest.  If  strontia  and  lime  alone  are  present,  separate  according 
to  28.  If  baryta  is  present,  separate  the  three  alkaline  earths  after  24. 

bb.  Although  it  is  possible  in  aa  to  test  for  metals  precipitable  by 
sulphu retted  hydrogen  from  acid  solution,  e.g.,  copper,  and  if  required 
to  determine  them,  still  it  is  more  convenient  to  employ  a fresh  quarter 
of  the  hydrochloric  acid  solution  for  this  purpose.  The  precipitate  ob- 
tained by  passing  the  gas  into  the  warm  dilute  solution  is  washed,  dried, 
and  treated  with  bisulphide  of  carbon.  If  a residue  remains  it  is  to  be 
examined. 

cc.  The  remaining  quarter  of  the  dilute  hydrochloric  acid  solution  is 
used  for  the  estimation  of  the  alkalies :\  Mix  with  chlorine  water,  then 
with  ammonia  and  carbonate  of  ammonia ; after  allowing  the  mixture  to 
stand  for  some  time,  filter  off  the  precipitate,  evaporate  the  filtrate  to 
dryness,  ignite  the  residue  in  a platinum  dish  to  remove  the  ammonia 
salts,  and  finally  separate  the  magnesia  from  the  alkalies  as  directed  p. 
345,  15.  The  reagents  must  he  most  carefully  tested  for  fixed  alkalies, 
and  the  use  of  glass  and  porcelain  vessels  avoided  as  far  as  practicable. 

Should  the  limestone  contain  a sulphate  soluble  in  hydrochloric  acid, 
precipitate  the  sulphuric  acid  by  a small  excess  of  chloride  of  barium, 
allow  to  settle,  and  filter  off  the  sulphate  of  baryta  (which  is  to  be 
determined  in  the  usual  manner)  before  proceeding  as  above  to  the  esti- 
mation of  the  alkalies. 

h.  As  calcite  and  aragonite  may  contain  Jluorides  (JenzschJ),  the 
possible  presence  of  fluorine  must  not  be  disregarded  in  accurate  analy- 
ses of  limestones.  Treat,  therefore,  a larger  sample  of  the  mineral  with 
acetic  acid  until  the  carbonate  of  lime  and  carbonate  of  magnesia  are 
decomposed ; evaporate  to  dryness  until  the  excess  of  acetic  acid  is  com- 
pletely expelled,  and  extract  the  residue  with  water  (§  138,  I.).  We 
have  the  fluorine  in  the  residue.  If  it  can  be  distinctly  detected  in  a 
portion  of  the  same,||  the  determination  may  be  attempted  after  § 166,  5. 

i.  If  the  limestone  under  examination  contains  chlorides,  treat  a large 
sample  with  water  and  nitric  acid,  at  a very  gentle  heat ; filter,  and  pre- 
cipitate the  chlorine  from  the  filtrate  by  solution  of  nitrate  of  silver. 

k.  It  is  often  interesting  for  agriculturists  to  know  the  degree  of  solu- 


* Zeitschrift  f analyt.  Chem.  1,  474. 

f The  simplest  way  of  ascertaining  whether  and  what  alkalies  are  present  in  a 
limestone,  is  the  process  given  by  Engelbach  (Annal.  d.  Chem  u.  Phar-m.  123, 
260)  — viz. , ignite  a portion  of  the  triturated  mineral  strongly  in  a platinum  cru- 
cible over  the  blast,  boil  with  a little  water,  filter,  neutralize  with  hydrochloric 
acid,  precipitate  with  ammonia  and  carbonate  of  ammonia,  filter,  evaporate  the 
filtrate  to  dryness  and  examine  with  the  spectroscope.  The  carbonate  of  ammo- 
nia precipitate  may  be  evaporated  with  hydrochloric  acid  to  dryness,  and  exam- 
ined in  like  manner  for  baryta  and  strontia. 

% Pogg.  Annal.  96,  145.  ||  See  Qual.  Anal.  § 146,  6. 


523 


§ 222. J ANALYSIS  OF  LIMESTONES,  DOLOMITES,  MARLS,  ETC. 

bility  of  a sample  of  limestone  or  marl  in  the  weaker  solvents.  This 
may  be  ascertained  by  treating  the  sample  first  with  water,  then  with 
acetic  acid,  finally  with  hydrochloric  acid,,  and  examining  each  solution 
and  the  residue.  The  analyses  of  marls  made  by  C.  Struckmann*  were 
done  in  this  manner. 

1.  To  effect  the  separation  of  the  caustic  or  carbonated  lime,  in  hy- 
draulic limes,  from  the  silicates,  Deville  f proposed  to  boil  with  solution 
of  nitrate  of  ammonia,  which  he  stated  would  dissolve  the  caustic  lime 
and  carbonate  of  lime,  without  exercising  a decomposing  action  on  the 
silicates.  Gunning  J found,  however,  that  by  this  process  the  double 
silicates  of  alumina  and  lime  are  more  or  less  decomposed,  with  separa- 
tion of  silicic  acid.  As  yet  no  method  is  known  by  which  the  object 
here  stated  can  be  accomplished  with  absolute  accuracy  ; the  best  way, 
perhaps,  is  treating  the  sample  with  dilute  acetic  acid  ; C.  Knausz  |{ 
recommends  hydrochloric  acid. 

B.  Volumetric  Determination  of  Carbonate  of  Lime  and  Carbon- 
ate of  Magnesia  (for  technical  purposes). 

§ 222. 

a.  If  a mineral  contains  only  carbonate  of  lime,  the  amount  of  the 
latter  may  be  estimated  from  the  quantity  of  acid  required  to  effect  its 
decomposition,  the  method  described  in  § 210  being  employed  for  the 
purpose.  Or  the  carbonic  acid  in  the  mineral  may  be  determined,  say 
by  the  method  described  p.  291,  cc,  and  1 eq.  carbonate  of  lime  = 50 
calculated  for  each  eq.  carbonic  acid  ==  22. 

b.  But  if  the  mineral  contains,  besides  carbonate  of  lime,  also  carbo- 
nate of  magnesia,  the  results  obtained  by  either  process  give  the  quan- 
tity of  carbonate  of  lime  4-  carbonate  of  magnesia,  the  latter  being  ex- 
pressed by  its  equivalent  quantity  of  carbonate  of  lime  ( i.e .,  50  of 
carbonate  of  lime  for  42  of  carbonate  of  magnesia).  If,  therefore,  you 
desire  to  know  the  actual  amount  of  each,  you  must,  in  addition  to  the 
above  determination,  estimate  one  of  the  earths  separately.  For  this 
purpose  one  of  the  two  following  methods  may  be  employed  : — 

1.  Mix  the  dilute  solution  of  2 — 5 grm.  of  the  mineral  with  ammo- 
nia and  oxalate  of  ammonia  in  excess,  allow  to  stand  for  12  hours  and 
then  filter.  ' Ignite  the  precipitate  of  oxalate  of  lime,  together  with  the 
filter,  and  treat  the  carbonate  of  lime  produced  as  directed  § 210.  This 
process  gives' the  amount  of  lime  contained  in  the  analyzed  mineral; 
the  difference  between  this  and  the  former  result  gives  the  carbonate  of 
liine  which  is  equivalent  to  the  amount  of  carbonate  of  magnesia  present. 
To  obtain  perfectly  accurate  results  by  thig  method,  repeated  precipi- 
tation is  indispensable  (see  § 154,  6,  a). 

2.  Dissolve  2 — 5 grm.  of  the  mineral  in  the  least  possible  excess  of 
hydrochloric  acid,  and  add  a solution  of  lime  in  sugar  water  as  long  as  a 
precipitate  forms.  By  this  operation  the  magnesia  only  is  precipitat- 
ed. Filter,  wash,  and  treat  the  precipitate  as  directed  § 210  ; the  result 
represents  the  quantity  of  the  magnesia.  Deduct  the  quantity  of  car- 


* Annal.  d Chem.  u.  Pharm.  74,  170. 
f Compt.  rend,  37,  1001  ; Joum.  f.  prakt.  Chem.  62,  81. 

X Journ.  f.  prakt.  Chem.  62,  318. 

| Gewerbeblatt  aus  Wurtemberg,  1855,  Nr.  4;  Chem.  Centralbl.,  1855,  244. 


524 


SPECIAL  PART. 


bonate  of  lime  equivalent  thereto  from  the  result  of  the  total  determi- 
nation ; the  remainder  is  the  amount  of  carbonate  of  lime  present. 

The  method  2 is  only  suitable  when  the  proportion  of  magnesia  is  small. 

[11.  Analysis  of  Iron  Ores. 

§ 223. 

The  ore  is  averaged,  a sample  of  3 — 10  grm.  is  finely  pulverized,  and 
the  air-dry  substance  is  preserved  in  a tightly  stoppered  bottle. 

A.  Estimation  of  Iron. 

Solution.  In  case  of  spathic  iron  and  hydrous  hematites,  the  ore  (1 
grm.)  may  be  dissolved  in  strong  hydrochloric  acid  with  aid  of  a gentle 
heat.  In  presence  of  protoxide  of  iron,  sulphides,  or  organic  matters, 
add  powdered  nitre,  and  heat  until  these  substances  are  oxidized,  then 
cautiously  add  sulphuric  acid  in  excess,  and  evaporate  until  fumes  of 
this  acid  appear.  A residue  of  silica  may  be  disregarded,  unless  its  quan- 
tity be  so  large  as  to  interfere  with  accurate  division  of  the  solution.  In 
the  latter  case  it  must  be  filtered  off.  Dilute  to  100  c.  c.  If  the  ore  be 
slowly  soluble  or  insoluble  in  hydrochloric  acid,  it  is  best  to  mix  it  well 
with  thrice  its  weight  of  carbonate  of  soda  (if  sulphides  or  organic  matters 
be  present,  roast  the  ore  in  a porcelain  crucible  before  mixing  with  soda, 
or  add  to  the  mixture  a suitable  proportion — y1^ — of  pulverized  nitre) 
and  fuse  for  15  minutes.  Dissolve  the  fused  mass  with  a small  bulk  of 
dilute  sulphuric  acid  (1  volume  of  acid  to  4 volumes  of  water),  if  nitre 
was  employed,  or  silica  is  present  in  the  fusion,  evaporate  until  vapors 
of  sulphuric  acid  arise,  and  dilute  to  100  c.  c. 

Determination  oftlce  iron  is  made  volumetrically,  on  portions  of  25  c.  c., 
either  with  permanganate  of  potassa  after  previous  reduction  by  means 
of  zinc,  or  directly  by  standard  solution  of  hyposulphite  of  soda,  p.  203. 

In  presence  of  titanium  the  latter  method  must  be  employed,  because 
titanic  acid  is  partially  reduced  by  zinc,  as  shown  by  the  purple  tint  of 
the  solution. 

B.  Estimation  of  Iron,  Manganese,  Silica,  and  Phosphoric  Acid. 

The  ore  (2  grm.)  is  fluxed  with  carbonate  of  soda  as  described  in  A, 
dissolved  in  dilute  sulphuric  acid,  evaporated  and  heated  until  fumes  of 
sulphuric  acid  begin  to  appear,  treated  with  water,  and  filtered  off  from 
silica.  The  filtrate  is  diluted j>r  concentrated  to  200  c.  c.  and  iron  es- 
timated in  portions  of  25  c.  c.,  by  hyposulphite,  p.  203.  Erom  100 
c.  c.  the  iron  is  thrown  down  by  acetate  of  soda,  p.  123,  e. 

Manganese  is  estimated  in  the  filtrate  by  precipitation  with  bromine, 
p.  184,  d,  and  if  the  quantity  be  large,  by  subsequent  conversion  into 
pyrophosphate.  The  operator  must  not  omit  to  satisfy  himself  of  the 
complete  separation  of  manganese,  by  testing  the  clear  liquid  or  filtrate 
with  bromine  and  warming.  If  the  solution  is  or  becomes  strongly 
acid,  nearly  neutralize  it  with  carbonate  of  soda  before  adding  bro- 
mine. The  final  filtrate  from  the  bromine  precipitates  should  be  neu- 
tralized with  ammonia  and  tested  with  sulphide  of  ammonium,  p.  184,  e, 
in  order  to  be  certain  of  the  complete  precipitation  of  manganese. 


ASSAY  OF  COPPER  ORES. 


525 


§ 224.] 

Phosphoric  acid , if  present,  exists  in  the  precipitate  by  acetate  of  soda. 
This  is  dissolved  in  nitric  acid,  diluted  to  200  c.  c and  precipitated  by 
means  of  molybdenum  solution.  The  phosphoric  acid  is  weighed  as  py- 
rophosphate of  magnesia.  The  directions  found  on  p.  271  must  be 
strictly  followed.  If  arsenic  acid  be  present,  this  must  be  removed  by 
passing  sulphuretted  hydrogen  at  70°  through  the  sulphuric  solution, 
which,  after  removal  of  the  sulphide  of  arsenic,  must  be  heated  with 
nitric  acid  to  peroxidize  the  iron. 

C.  Estimation  of  Sulphur. 

In  presence  of  pyrites  fuse  the  ore  (1 — 3 grm.)  with  thrice  its 
weight  of  carbonate  of  soda  and  nitre,  both  free  from  sulphur,  in  a 
porcelain  dish,  acidulate  with  hydrochloric  acid,  evaporate  to  dryness 
over  the  water-bath  to  separate  silica,  and  precipitate  with  chloride 
of  barium.  To  purify  the  BaO  S03,  when  yellow  from  presence  of  iron, 
fuse  it  with  carbonate  of  soda,  extract  the  fused  mass  with  water,  aci- 
dulate the  aqueous  solution  (filtered  off  from  Fe2  03  and  BaO  C02)  with 
hydrochloric  acid,  and  precipitate  again  with  chloride  of  barium. 

D.  Estimation  of  Titanium. 

Titanium  is  estimated  in  1 — 5 grm.  of  ore,  which  should  be  fused 
with  soda,  the  fused  mass  dissolved  in  excess  of  sulphuric  acid,  evapo- 
rated to  dryness  cautiously  in  an  air-bath,  the  heat  being  gradually  rais- 
ed until  the  bisulphate  of  soda  formed  passes  into  fusion  at  a low  red 
heat.  Cover  the  cold  mass  with  cold  water,  let  stand  a number  of  hours 
until  it  is  thoroughly  softened  and  dissolved,  dilute  to  500 — 700  c.  c., 
filter  off  from  silica,  add  bisulphite  of  soda  to  reduce  the  iron  to  pro- 
toxide, heat  to  boiling  for  an  hour  or  more,  replacing  the  evaporated 
water,  and  adding  bisulphite  of  soda,  or  solution  of  sulphurous  acid, 
from  time  to  time.  The  titanic  acid  is  then  thrown  down  completely, 
provided  too  much  free  sulphuric  acid  be  not  present.  Filter  and  wash 
with  hot  water.  To  the  filtrate  and  washings  add  more  sulphurous  acid, 
or  sulphite,  and  if  strongly  acid  nearly  neutralize  with  carbonate  of 
soda,  and  boil  for  thirty  minutes  longer  ; filter  off  any  additional  preci- 
pitate, and  repeat  the  operation  as  long  as  titanic  acid  separates.  Test 
100  c.  c.  of  the  last  filtrate  by  concentrating  with  sulphuric  acid  and 
zinc,  to  be  certain  that  all  titanic  acid  is  precipitated.  The  impure 
titanic  acid  thus  obtained  is  ignited  and  weighed,  see  p.  1 78.  It  is 
then  redissolved  by  fusion  with  bisulphate  of  soda,  and  treatment  with 
cold  wafer,  and  either  reprecipitated  by  boiling  its  solution,  mixed  with 
sulphurous  acid  as  before,  in  order  to  obtain  it  free  from  iron,  or  the 
iron  may  be  determined  volumetrically  in  the  solution  by  means  of 
hyposulphite  of  soda,  p.  203,  3,  h , and  the  titanic  acid  estimated  by  dif- 
ference.] 

12.  Assay  of  Copper  Ores.* 

§ 224. 

A.  Mohr’s  Method  for  Oxides , Silicates,  and  Carbonates  of  Copper . 

Powder  the  ore  finely ; if  rich,  take  1 grm.,  if  poor,  3 grm.  Treat  in 

* See  also  Steinbeck’s  Method,  Chemical  News,  v.  19,  p.  207,  and  Luckow’s 
Method,  idem.  p.  221. 


526 


SPECIAL  PART. 


a porcelain  dish  of  10  cm.  diameter  with  some  sulphuric  acid,  water,  and 
nitric  acid,  cover  the  dish  with  a large  watch-glass  and  heat  to  boiling. 
As  soon  as  the  mass  is  nearly  dry  and  ceases  to  spirt,  remove  the  watch- 
glass  and  increase  the  flame,  maintaining  an  elevated  temperature  till 
no  more  fumes  escape ; allow  to  cool,  add  distilled  water,  heat  to  boiling, 
filter  into  a small  platinum  dish,  wash  with  hot  water,  evaporate  the 
washings  and  transfer  them  also  to  the  platinum  dish,  and  finally — hav- 
ing made  quite  sure  that  the  residue  insoluble  in  water  gives  up  no  cop- 
per to  acids — precipitate  the  copper  with  zinc,  after  p.  229,  2,  a.  The 
light-red  color  of  the  copper  is  an  indication  of  its  purity.  'It  will  be 
seen  that  we  have  in  view  in  this  process  the  removal,  as  far  as  possible,  of 
the  metals  precipitable  by  zinc,  viz. : lead,  antimony,  and  tin.  [Arsenic 
is  not  fully  removed,  and  in  this,  as  in  the  following  processes,  must  be 
separated  by  sulphide  of  sodium.  128,  p.  329.] 

[B.  Gibbs’  Method  for  Sulphides* 

Mix  the  finely  pulverized  ore  in  a porcelain  crucible  with  3 — 4 times  its 
weight  of  a mixture  of  10  parts  of  nitre,  and  14  parts  of  bisulpliate  of 
potash.  Heat  the  whole  slowly  to  low  redness — best  in  a muffle.  The 
sulphides  are  completely  oxidized  without  frothing.  Add  enough  sul- 
phuric acid  to  convert  all  the  sulphate  of  potash  into  bisulphate,  and 
heat  again  carefully  until  the  contents  of  the  crucible  fuse  to  a clear 
mass.  Dissolve  in  water,  filter  from  silica,  etc.,  and  precipitate  the  cop- 
per as  described  p.  229,  6.] 

[C.  Storer  and  Pearson’s  Method  for  Sulphides.\ 

The  ore,  2 — 5 grm.,  is  pulverized  and  mixed  with  its  bulk  of  powdered 
chlorate  of  potash  in  a porcelain  dish,  and  covered  with  a watch-glass  or 
inverted  funnel ; add  nitric  acid  of  ordinary  strength,  rather  more  than 
would  be  sufficient  to  cover  the  powder.  Heat  to  gentle  ebullition,  add- 
ing from  time  to  time  chlorate  of  potash,  if  needful,  until  the  sulphur  is 
completely  oxidized.  Binse  the  cover  into  a separate  beaker.  When  the 
contents  of  the  porcelain  dish  are  cold,  add  a quantity  of  strong  hydro- 
chloric acid,  rather  larger  than  the  quantity  of  nitric  acid  first  employed ; 
evaporate  the  whole  to  dryness,  to  render  silica  insoluble.  Treat  the 
residue  with  water,  and  mix  the  whole  with  the  rinsings.  Heat  the  liquid 
nearly  to  boiling,  and  add  strong  solution  of  protosulphate  of  iron, 
slightly  acidulated  with  sulphuric  acid ; keep  the  whole  hot  until  the 
contents  of  the  beaker  become  almost  black,  and  no  more  gas  is  disen- 
gaged. 

When  the  nitric  acid  has  been  reduced  by  this  treatment,  filter  into 
a wide  beaker  and  precipitate  by  a clean  sheet  of  iron,  or  by  a flat  coil 
of  iron  wire.  Wash  the  metallic  copper  with  water,  then  with  alcohol, 
and,  if  need  be,  ignite  it  in  a current  of  hydrogen  before  weighing.];] 

[*  Am  Journ.  Sci. , xliv.  212.] 

[f  Am.  J oum.  Sci. , xlviii.  194.  ] 

[f  The  precipitation  by  iron  succeeds  well  when  iron  can  be  obtained  which 
dissolves  in  dilute  acid  without  the  separation  of  black  particles  or  flakes  in  weigh- 
able  quantity.  If  the  copper  solution  be  cold,  dilute,  and  nearly  neutral  when  the 
iron  is  first  placed  in  it,  the  copper  has  little  adhesion  to  the  iron,  and  may  be  readily 
detached  from  it  for  the  purpose  of  weighing.  If,  as  soon  as  the  iron  is  coated 
with  copper,  hydrochloric  acid  (20  c.  c.)  be  added,  and  the  whole  be  heated  to 
near  the  boiling-point,  and  maintained  at  that  temperature,  but  without  ebulli- 
tion. the  residue  of  the  copper  is  deposited  as  a spongy  coherent  mass,  which, 


225.] 


ANALYSIS  OF  GALENA. 


527 


\ 


13.  Analysis  of  Galena. 

§ 225. 

This  is  the  most  widely  spread  of  the  lead  ores.  It  frequently  con- 
tains larger  or  smaller  quantities  of  iron,  copper,  and  silver,  occasion- 
ally traces  of  gold,  and  commonly  also  more  or  less  gangue,  insoluble  in 
acids. 

Reduce  the  ore  to  a fine  powder,  and  dry  at  100°. 

Oxidize  a weighed  quantity  (1 — 2 grm.)  with  highly  concentrated  red 
fuming  nitric  acid,  free  from  chlorine  and  sulphuric  acid  (see  p.  326). 
For  this  purpose  use  a capacious  flask,  covered  during  the  operation  with 
a watch-glass ; do  not  put  the  tube  in  which  the  powder  was  weighed 
into  the  flask.  If  the  acid  is  sufficiently  strong,  the  sulphur  will  be 
fully  oxidized.  After  you  have  warmed  gently  for  a long  time,  add  3 or 
4 c.  c.  pure  concentrated  sulphuric  acid,  which  you  have  previously  di- 
luted with  a little  water,  and  heat  on  an  iron  plate,  till  all  the  nitric 
acid  is  evaporated.  Dilute  with  water,  filter,  wash  the  residue  with 
water  containing  sulphuric  acid,  and  displace  the  latter  with  alcohol. 
Collect  the  alcoholic  washings  separately. 

a.  Dry  the  residue , ignite,  and  weigh  (§  116,  3).  It  consists  of  sul- 
phate of  lead,  gangue  undecomposed  by  the  acid,  silicic  acid,  &c.  Heat 
the  whole,  or  a fractional  part,  with  hydrochloric  acid  to  boiling ; let 
the  insoluble  matter  subside,  and  then  decant  the  supernatant  clear 
liquid  on  to  a filter ; pour  a fresh  portion  of  hydrochloric  acid  on  the 
residue,  boil  again,  allow  to  subside,  and  decant,  and  repeat  this  opera- 
tion until  the  sulphate  of  lead  is  completely  dissolved  ; finally,  place  the 
residue  on  the  filter,  and  wash  with  boiling  water  until  every  trace  of 
chloride  of  lead  is  removed ; dry,  ignite,  and  weigh  the  residue.  Sub- 
tract the  weight  found  from  that  of  the  original  residue  : the  difference 
expresses  the  quantity  of  sulphate  of  lead  which  the  latter  contained. 
Instead  of  using  hydrochloric  acid,  the  sulphate  of  lead  may  also  be  dis- 
solved by  heating  with  an  aqueous  solution  of  tartrate  or  acetate  of  am- 
monia and  caustic  ammonia ; or  it  may  be  first  converted  into  carbonate 
of  lead,  by  digestion  with  solution  of  carbonate  of  soda,  washed  and 
dissolved  in* dilute  nitric  acid. 

b.  The  sulphuric  acid  solution  is  free  from  any  weighable  trace  of  lead, 
if  the  process  has  been  properly  conducted.  It  contains  the  metals  pre- 
sent in  the  ore  in  addition  to  lead.  First  add  some  hydrochloric  acid, 
to  precipitate  the  silver , if  present.  If  a turbidity  or  precipitate  is 
formed,  keep  the  fluid  for  some  time  in  a warm  place,  till  the  chloride 
of  silver  has  subsided.  The  latter  is  filtered  off  and  may  be  determined 
after  § 115,  1.  In  the  case  of  very  small  quantities,  I prefer  to  incin- 
erate the  filter  with  the  precipitate  in  a porcelain  crucible,  to  ignite  the 
residue  for  a short  time  in  hydrogen,  to  dissolve  the  trace  of  metallic 
silver  in  nitric  acid,  to  evaporate  the  solution  in  the  crucible  to  dryness, 
to  take  up  the  residue  with  water,  and  to  estimate  the  silver  in  the  solu- 
tion by  Pisani’s  method  (p.  215). 

with  care,  may  be  removed  from  the  iron  and  washed  without  falling-  to  pieces 
or  oxidizing-  (see  p.  229,  2,  «,  for  details  of  washing-).  If  the  copper  should  be 
difficult  to  collect  by  decantation,  it  may  be  gathered  on  a small  filter,  and,  after 
burning  the  latter,  may  be  either  reduced  by  hydrogen  or  calcined  to  oxide  (p. 
229,  bottom).] 


528 


SPECIAL  PART. 


[§  226. 


Precipitate  the  fluid  filtered  from  the  chloride  of  silver  with  sulphu- 
retted hydrogen.  The  precipitate  generally  contains  a little  sulphide  of 
copper , occasionally  also  other  sulphides.  Separate  these,  as  well  as  the 
metals  in  the  filtrate,  which  are  precipitable  by  sulphide  of  ammonium 
( iron , zinc , &c.),  according  to  the  methods  of  Section  Y. 

The  foregoing  method  does  not  enable  the  assayer  to  determine  very 
small  quantities  of  silver*  and  the  trifling  traces  of  gold  which,  accord- 
ing to  Percy  and  Smith, f are  often  found  in  galena.  To  effect  this,  it 
is,  in  the  first  place,  necessary  to  produce  a button  containing  the  whole 
or  part  of  the  lead  of  the  galena,  and  the  whole  of  the  silver  and  gold, 
and  then  to  separate  the  latter  metals.  This  is  accomplished  as  described 
in  § 226  and  § 227. 

[For  the  estimation  of  the  sulphur,  take  a fresh  portion  of  the  pulver- 
ized ore  and  bring  it  into  solution  by  method  C,  p.  526,  filter  from  silica, 
in  presence  of  iron,  add  a lump  of  solid  tartaric  acid,  precipitate  hot  by 
chloride  of  barium,  and  wash  by  decantation  first  with  hot  water,  and 
finally  with  dilute  solution  of  acetate  of  ammonia.  The  tartaric  acid 
prevents  precipitation  of  iron,  the  acetate  of  ammonia  purifies  the  pre- 
cipitate from  alkali  and  baryta  salts. — Storer  and  Pearson.J] 

[14.  Silver  Assay. 

§ 226. 

Assay  by  Scorif  cation  and  Cupellation. 

A.  Ores  Poor  in  Silver. 

1.  j Preparation  of  the  Ore.  The  well-sampled  ore  is  pulverized  and 
passed  through  a sieve  with  60  to  80  holes  to  the  linea,r  inch.  If  par- 
ticles of  metallic  silver  or  malleable  ore  remain  upon  the  sieve,  they 
must  be  assayed  separately. 

The  fluxes  required  are,  1,  Assay  lead , prepared  by  shaking  melted 
lead  in  a wooden  box  and  sifting  through  meshes  of  inch  ; 2,  JBorax 
or  borax-glass  y and  3,  Quartz  sand  or  powdered  glass , to  form  silicates 
with  the  metallic  and  earthy  oxides,  and  also  sometimes  to  prevent  the 
oxide  of  lead  from  destroying  the  scorifier.  The  proportions  of  the 
fluxes  vary  with  different  ores,  and  should  be  sufficient  to  form  a liquid 
slag  and  a lead  button  of  convenient  size.  The  addition  of  too  much 
borax  will  envelop  the  metallic  lead  before  sufficient  oxide  of  lead  is 
formed  to  decompose  the  silver  compounds. 

Galena  requires  6 parts  lead  and  no  borax  ; quartzose  ores  about  8 
parts  and  no  borax  ; blende,  mispickel,  and  pyrites  about  16  parts,  and 
^ to  1 part  borax  ; copper  and  tin  compounds  20  to  30  of  lead,  and 
nickel  and  cobalt  even  more  ; nickelspeise  1 6 parts  of  lead  and  repeated 
scorifications  ; ores  containing  calcite,  dolomite,  barytes,  or  fluorspar,  8 
parts  of  lead  and  12  parts  borax  or  glass.  In  case  of  doubt  as  to  the 
nature  of  the  ore,  begin  with  8 parts  of  lead,  and,  if  the  fusion  is  not 
good,  repeat  with  a larger  proportion  of  lead. 


* Argentiferous  galenas  generally  contain  only  between  0*03  to  048,  rarely 
above  0’5R  silver  ; and  a great  many  contain  far  less  than  0-03ft. 

f Phil.  Mag. , VII.  126.  % Am.  Jour.  Sci. , XLVIII.  193. 


§ 320.] 


SILVER  ASSAY. 


529 


2.  Scorification.  The  objects  of  this  process  are  to  concentrate  all  the 
silver  in  a lead  button,  to  decompose  the  sulphides,  etc.,  and  to  dissolve 
and  slag  off  earthy  and  other  substances  by  means  of  the  oxide  of  lead 
formed. 

In  this  process  all  the  sulphur  of  the  heavy  metallic  sulphides  passes 
off  finally  as  sulphurous  acid.  Sulphides  of  the  alkalies  and  of  the 
alkaline  earths,  if  present,  are  oxidized  to  sulphates. 

Charge  and  f usion.  2 to  4 grammes  of  the  sampled  ore  are  mixed 
with  half  the  assay  lead  required,  placed  in  a scorifier,*  and  covered  with 
the  remainder  of  the  assay  lead.  If  borax  is  used,  it  is  best  placed  on 
top  of  the  assay,  but  glass  should  be  mixed  with  it.  The  charged 
scorifier  is  placed,  with  help  of  suitable  tongs,  in  a red  hot  muffle.  (If 
no  muffle  is  at  hand,  the  fusion  may  be  made  in  a large  Hessian  cruci- 
ble, which  is  laid  on  its  side  on  a good  bed  of  coals,  and  partly  covered 
with  charcoal.  The  mouth  can  be  closed  with  a crucible  cover.)  A piece 
of  glowing  charcoal  is  placed  on  or  by  the  scorifier,  the  mouth  of  the 
muffle  is  closed,  and  the  heat  kept  up.  The  lead  soon  fuses,  and  the 
ore,  being  lighter,  floats  on  the  surface  and  roasts.  From  the  appear- 
ance of  the  fumes  the  assayer  can  frequently  judge  of  the  nature  of  the 
ore  ; sulphur  giving  light  gray,  zinc  thick  white,  arsenic  grayish,  and 
antimony  bluish  fumes.  After  15  to  20  minutes  the  assay  has  melted 
down,  and  a fluid  slag  has  formed  at  the  periphery  of  the  glowing 
metal ; the  latter  meantime  gives  off  fumes  of  oxide  of  lead.  With  diffi- 
cultly fusible  ores  it  may  require  30  minutes  for  complete  fusion,  and  even 
then  it  may  be  necessary  to  add  more  lead  or  borax.  The  latter  should 
be  wrapped  in  stiff  paper  and  placed  on  the  assay  with  tongs.  The 
paper  keeps  the  borax  from  contact  with  the  assay  till  its  water  is  driven 
off,  thus  preventing  a loss  by  sputtering.  If  the  ore  contains  much 
zinc,  it  is  better  to  volatilize  this  metal  by  covering  the  scorifier  with 
glowing  coals,  closing  the  muffle  and  increasing  the  heat,  as  oxide  of 
zinc  forms  a stiff  slag.  The  muffle  is  now  opened,  and  the  slagging  is 
allowed  to  proceed  at  a temperature  just  high  enough  to  keep  the  lead 
bright.  A high  heat  hastens  the  process,  but  causes  a loss  of  silver  by 
oxidation  and  volatilization.  When  the  slag  covers  the  button,  the 
heat  is  increased  for  a few  minutes,  in  order  to  separate  any  metallic 
lead  which  -may  be  mechanically  mixed  with  it.  The  assay  is  now 
poured  into  a casting-plate, f previously  warmed,  to<  expel  the  moisture. 
If  no  casting-plate  is  at  hand,  the  assay  may  be  allowed  to  cool  in,  the 
scorifier. 

The  button  should  separate  easily  from  the  slag,  and  must  be  per- 
fectly malleable.  It  is  entirely  freed  from  adhering  slag  by  hammering 
into  a cubical  mass,  and  is  then  ready  for  the  process  of  cupellation, 
unless  too  large,  in  which  case  it  must  be  reduced  in  bulk  by  reheating 
on  a fresh  scorifier.  If  the  button  be  hard,  or  contain  much  metallic 
copper,  more  lead  and  borax  are  added,  and  the  process  is  repeated. 
In  general  it  is  better  to  carry  the  scorification  as  far  as  possible,,  since 


* A cup  of  baked  clay,  to  be  had  of  dealers  in  apparatus, 
f The  casting-plate  is  a plate  of  sheet-copper  with  a handle,  and  12: — 20  cup- 
shaped depressions,  each  \\  inch  wide  and  £ inch  deep  ; it  is  convenient  when 
several  assays  are  carried  on  together.  The  cups  are  rubbed  with  chalk  to  pre- 
vent the  button  from  adhering. 

34 


530 


SPECIAL  PART. 


experience  has  shown  that  there  is  less  loss  of  silver  in  scorifiqation 
than  in  cupellation. 

3.  Cupellation  (§  163,  10  ; 122)-  This  process  consists  in  the  oxi- 
dation of  the  lead  on  a bone-ash  cupel,*  which  absorbs  the  oxide  of 
lead,  leaving  metallic  silver. 

The  cupel,  after  the  dust  is  blown  out,  is  placed  in  a muffle  and  heated 
to  redness  to  expel  the  moisture.  If  this  precaution  be  neglected, 
the  escaping  vapor  causes  a loss  of  the  alloy  by  sputtering.  The 
argentiferous  lead  is  carefully  placed  on  the  cupel,  a piece  of  glowing 
charcoal  is  laid  near  it,  the  mouth  of  the  muffle  is  closed,  and  the  whole 
is  brought  promptly  to  fusion.  If  it  is  not  quickly  fused,  particles  of 
the  assay  are  liable  to  stick  to  the  sides  of  the  cupel,  causing  a loss.  As 
soon  as  the  assay  has  “ cleared, the  muffle  should  be  opened,  the  char- 
coal removed,  and  the  heat  lowered  near  the  assay,  either  by  closing 
the  draughts  or  moving  the  cupel  nearer  the  mouth  of  the  muffle. 
The  oxidation  should  now  be  earned  on  at  as  low  a heat  as  possible,  as 
a high  heat  increases  the  volatilization  of  the  silver  along  with  the 
lead.  If  the  temperature  is  right,  imperfect  crystals  of  oxide  of  lead 
form,  and  the  fumes  rise  to  the  middle  of  the  muffle  ; but  if  the  fumes 
disappear  immediately  above  the  cupel,  whilst  the  latter  is  at  a bright 
red  heat,  and  no  crystals  form,  the  heat  is  too  high.  If,  on  the  other 
hand,  the  cupel  is  dark  brown,  and  thick  fumes  rise  to  the  top  of  the 
muffle,  the  heat  is  too  low,  and  there  is  danger  of  solidification.  If  the 
assay  M freezes  ” or  solidifies,  it  may  be  again  fused ; the  results  are, 
however,  too  low,  as  silver  passes  into  the  bone-ash.  Alloys  containing 
copper  require  a higher  heat  to  prevent  freezing.  Towards  the  close 
of  the  operation  the  heat  should  be  gradually  raised,  as  the  alloy  becomes 
less  fusible  with  the  increased  proportion  of  silver,  and  the  lead  oxidizes 
with  more  difficulty.  When  the  cupellation  is  nearly  finished,  a play 
of  colors  is  seen,  and  the  button  suddenly  brightens  or  “ blicks,”  and 
becomes  white,  and  is  free  from  lead.  It  is  immediately  moved  towards 
the  mouth  of  the  muffle,  so  as  to  cool  slowly.  If  suddenly  cooled  it 
cf  sprouts,”  sometimes  throwing  particles  out  of  the  cupel,  owing  to  the 
sudden  escape  of  the  oxygen  which  molten  silver  absorbs,  unless  it 
contains  copper,  lead,  or  much  gold. 

The  button  must  separate  easily  from  the  cupel.  It  is  taken  up  by 
pincers  and  brushed  with  a stiff'  brush.  It  should  be  well  rounded  and 
bright,  show  no  particles  of  bone-ash  under  a magnifying  glass,  and  have 
no  projecting  ridges  caused  by  cracks  or  depressions  in  the  cupel,  as 
these  always  contain  lead.  The  silver  obtained  is  not  chemically  pure, 
but  the  amount  of  foreign  matters  is  so  small  that  no  notice  is  taken  of 
them  in  ore  assays,  and  moreover,  the  impurities  do  not  compensate  for 
the  loss  in  scorification  and  cupellation.  The  assay  lead  must  be  assayed, 
and  the  amount  of  silver  yielded  by  it  must  be  deducted  from  that  ob- 
tained from  the  ore.  The  weight  of  silver  in  milligrammes,  multiplied 
by  '££4,  gives  the  number  of  troy  ounces  per  ton  of  ore. 

1 Troy  ounce  of  pure  silver  is  worth  $1.29  gold. 


* Cupels  are  most  conveniently  purchased  of  the  dealers  in  apparatus.  They 
should  be  neither  too  porous  nor  too  compact.  In  the  former  case  silver  passes 
into  the  bone-ash,  in  the  latter  the  oxide  of  lead  is  not  absorbed  with  sufficient 
rapidity. 

\ i.e.  Exposes  a bright  surface  of  lead. 


GOLD  ASSAY. 


531 


§ 227.] 

Silver  ores  may  be  assayed  by  the  methods  described  in  § 227  for 
the  assay  of  gold  ores,  but  the  results  obtained  are  not  as  high  as  by  the 
scorification  method. 

B.  Ores  rich  in  Silver. 

Ores  of  1 per  cent,  or  more  are  assayed  as  described  under  A,  but  the 
loss  by  volatilization  impairs  somewhat  the  accuracy  of  the  result. 

C.  Bullion. 

Alloys  are  assayed  either  in  the  wet  way  or  by  cupellation,  as  de- 
scribed under  A,  3.  When  the  assay  contains  more  than  1 per  cent,  of 
silver,  the  loss  by  volatilization  must  be  taken  into  the  account.  This 
is  done  by  the  method  of  assaying  with  “ proofs,”  i.  e.,  the  composition 
of  the  alloy  is  determined  approximately,  if  not  already  known,  by  a 
preliminary  cupellation,  and  then  a “proof”  is  made  up  of  the  same 
composition  as  the  assay,  by  weighing  off  the  proper  quantities  of  pure 
metals ; this  and  the  assay  are  then  melted  with  the  same  amount  of 
lead,  and  the  two  are  cupelled  together  side  by  side.  The  loss  of  the 
proof  is  added  to  the  result  of  the  assay.  The  numerous  details  of  the 
assay  with  proofs,  which  are  observed  in  order  to  accomplish  a large 
amount  of  work  in  a short  time,  are  properly  learned  in  assay  offices. 

15.  Gold  Assay. 

§ 227. 

Crucible  Assay  and  Parting. 

Ores  of  gold  may  also  be  assayed  by  the  scorification  method  (§ 
226),  but  on  account  of  the  difficulty  of  sampling,  it  is  better  to  take 
larger  amounts  of  ore  and  make  a crucible  fusion. 

Gold  ores  may,  for  convenience,  be  divided  into  two  classes.  First, 
those  containing  little  or  no  sulphur ; and  second,  those  containing  sul- 
phur, as  pyrites,  blende,  etc. 

A.  Ores  of  the  First  Class. 

1.  Reduction.  If  the  ore  consists  principally  of  quartz  or  silicates,  a 
fusion  with,  litharge  and  a reducing  flux  yields  a uniform  brittle  vitreous 
slag,  and  a lead  button  containing  the  gold  and  silver.  If  the  ore  con- 
tains basic  substances,  such  as  calcite,  oxide  of  iron,  etc.,  quartz  sand  or 
broken  glass  must  be  added. 

The  reducing  flux  mentioned  in  the  subsequent  directions  is  a mix- 
ture of  100  parts  of  bicarbonate  of  soda  and  20  parts  of  flour. 

The  following  is  a convenient  charge,  yielding  a button  that  may  be 


directly  cupelled : — 

Ore 50  grm. 

Litharge 75  grm. 

Reducing  flux 4 grm. 


If  glass  is  added,  count  it  as  ore,  and  increase  the  litharge  and  redu- 
cing flux  proportionally. 

Mix  thoroughly ; place  the  mixture  in  a clay  crucible,  which  should 
not  be  more  than  two-thirds  filled.  Cover  one-quarter  inch  deep  with 
dry  chloride  of  sodium,  and  lute  on  the  cover,  or  the  luting  may  be  omit- 
ted if  care  be  taken  that  no  coals  get  into  the  crucible.  The  fusion 


532  SPECIAL  PART.  [§  227. 

may  be  made  in  any  furnace  in  which  a white  heat  is  obtainable,  best  in 
a deep  wind  furnace. 

The  fire  is  kindled  at  the' top,  so  that  the  heat  shall  be  gradually  raised 
to  prevent  the  crucible  cracking.  A dull  red  heat  is  kept  up  for  half 
an  hour,  and  a white  heat  for  a quarter  of  an  hour  longer.  Too  high  a 
heat  for  an  unnecessary  length  of  time  is  to  be  avoided,  as  the  litharge 
is  liable  to  flux  the  crucible.  Remove  from  the  fire  while  hot,  and  tap 
gently  on  the  hearth  to  collect  the  lead  into  a button.  When  cool, 
crack  out  the  button,  which  should  separate  readily  from  the  slag,  and 
be  perfectly  malleable.  The  slag  should  be  uniform  and  vitreous,  show- 
ing a perfect  fusion,  and  should  include  no  metallic  globules. 

2.  Cupellation.  The  button  contains  the  gold  and  silver,  and  is  cu- 
pelled as  directed,  p.  530.  A higher  heat  is,  however,  necessary  to 
remove  the  last  traces  of  lead  than  if  no  gold  were  present.  There  is 
no  danger  of  sprouting  if  the  alloy  contains  much  gold. 

3.  Parting.  Clean  the  gold  globule,  as  directed  p.  530,  weigh,  and 
add  pure  silver  if  necessary,  so  that  the  alloy  shall  contain  2\  parts  silver 
to  1 of  gold.  The  proportion  of  additional  silver  required  in  an  ore-assay 
may  be  commonly  judged  from  the  color  of  the  alloy.  If  it  is  bright  yel- 
low, add  2\  parts,  if  only  faint  yellow,  2 parts,  and  if  white,  1 part  or  less. 

The  silver  and  the  alloy  are  fused  together  on  charcoal  before  the 
blowpipe,  or,  better  still,  are  wrapped  in  sheet  lead,  and  cupelled  at  a high 
heat.  The  button  is  hammered  and  rolled  into  a long  thin  leaf,  care 
being  taken  that  no  particles  crack  off.  If  large,  it  must  be  annealed 
during  the  rolling,  by  heating  on  a cupel  in  the  muffle. 

The  leaf  is  rolled  together  on  a slender  rod  or  pencil,  and  placed  in  an 
assay  flask,  or  large  test-tube,  and  boiled  with  dilute  nitric  acid,  sp.  gr. 
IT 6,  till  all  action  has  ceased  ; the  acid  is  decanted,  and  the  boiling  re- 
peated with  acid  of  sp.  gr.  T30. 

Wash  the  residual  gold  with  water  free  from  chlorine  till  the  wash- 
ings give  no  reaction  for  silver,  fill  the  flask  with  water,  cover  its  mouth 
with  a drying-cup*  or  porcelain  crucible,  and  invert.  The  gold  quickly 
settles  to  the  bottom  of  the  cup.  The  flask  is  slowly  raised  till  the  cup 
is  nearly  full  of  water,  and  is  then  quickly  drawn  off  one  side.  The 
water  is  carefully  poured  out  of  the  cup,  and  the  gold,  if  in  separate  par- 
ticles, is  collected  in  a drop  of  water  at  the  bottom.  After  thoroughly 
drying,  heat  to  redness  in  the  muffle,  but  not  to  fusion.  If  the  process 
has  been  properly  conducted  the  gold  remains  in  one  coherent  mass,  and 
may  be  readily  turned  into  a weighing-cup.  The  litharge  must  be  as- 
sayed for  silver  with  the  same  reducing  flux  as  was  used  with  the  ore. 

The  weight  of  the  button  obtained  by  cupellation,  less  that  of  the 
silver  yielded  by  the  litharge,  less  that  of  the  gold,  is  the  weight  of  the 
silver  in  the  ore. 

The  ounces  per  ton  are  calculated  as  directed  p.  530,  bottom. 

1 Troy  ounce  of  gold  has  a value  of  $20.66. 

B.  Ores  of  the  Second  Class  (containing  Sulphur). 

1.  Roasting  Process.  The  object  of  roasting  is  to  expel  the  sulphur, 
but  this  process  is  objectionable  on  account  of  the  mechanical  loss  of 
gold  occasioned  by  it.  The  operation  is  conducted  as  follows : A weighed 


* The  drying-cup  is  a deep  narrow  vessel  of  biscuit  ware. 


GOLD  ASSAY. 


533 


amount  of  the  ore  is  placed  in  an  iron  pan,  the  bottom  and  sides  of 
which  have  been  smeared  with  a paste  of  clay,  or  Venetian  red,  and  water. 
This  coating  serves  to  protect  the  iron  from  the  action  of  sulphur,  and 
should  be  slowly  and  thoroughly  dried  to  prevent  cracking.  The  roast- 
ing is  carried  on  at  a dull  red  heat,  with  frequent  stirring,  until  most  of 
the  sulphur  is  driven  off.  Towards  the  close  of  the  process  the  heat  is 
raised,  and  is  kept  up  till  the  odor  of  sulphurous  acid  is  no  longer  per- 
ceptible, and  a moistened  blue  litmus  paper  held  a few  inches  above  the 
ore  remains  unchanged.  The  ore  and  scrapings  from  the  pan  are  pulve- 
rized and  sifted.  The  following  are  the  proportions  of  the  charge : 

50  grms.  of  ore. 

20  “ powdered  glass. 

1 5 “ reducing  flux. 

100  “ litharge. 

Fuse  in  a crucible  and  cupel,  as  directed  for  ores  of  the  first  class. 

2.  Assay  by  Litharge  and  Nitre.  In  crucible  fusions  of  auriferous 
sulphides,  advantage  is  taken  of  their  reactions  with  oxide  of  lead. 
If  sulphides  are  fused  with  sufficient  litharge,  a button  of  lead  and  a 
slag  free  from  sulphur,  or  containing  the  sulphates  of  the  alkalies  or 
alkaline  earths,  are  obtained,  but  the  lead  button  is  too  large  for  scorifica- 
tion.  Pyrite  reduces  8|-  parts,  chalcopyrite  and  blende  7 parts,  gray  cop- 
per and  sulphide  of  antimony  about  6 parts  of  lead.  Nitre  is  added  to 
prevent  too  much  lead  being  reduced ; and,  to  determine  the  amount  of 
nitre  proper  to  use,  a preliminary  assay  is  made  by  fusing  3 to  5 grm. 
of  the  ore  with  50  parts  of  litharge.  The  fusion  should  be  made  quickly, 
using  care  to  prevent  the  action  of  reducing  gases,  and  as  soon  as  the 
mass  ceases  to  boil,  the  crucible  should  be  removed  from  the  fire,  to  pre- 
vent the  litharge  destroying  it.  The  resulting  button  is  weighed,  and 
the  amount  of  lead  that  would  be  yielded  by  the  ore  required  for 
an  assay  is  calculated.  If  this  amount  would  be  too  small  for  cupella- 
tion,  reducing  flux  must  be  added  ; if  of  the  right  size,  neither  reducing 
flux  nor  nitre  is  necessary,  but,  if  too  large,  nitre  must  be  added.  To 
find  the  weight  of  nitre  required  in  the  last  case,  deduct  the  weight  of 
the  button  desired  for  cupellation  (10 — 15  grm.)  from  the  weight  of  the 
lead  which  would  be  produced  by  fusing  the  charge  of  ore  with  litharge 
alone,  and  divide  the  remainder  by  four ; the  result  is  the  weight  of  nitre 
required.  The  oxidizing  power  of  commercial  nitre  varies  so  much  that 
it  is  better  to  determine  it  by  fusing  a sample  with  litharge  and  a redu- 
cing flux.  The  weight  of  lead  which  the  flux  alone  produces,  less  that 
obtained  when  a given  weight  of  nitre  is  added,  is  the  weight  of  lead  oxi- 
dized by  the  nitre.  The  charge  is  made  of  the  following  propor- 
tions : 

Ore,  20  grm. 

Litharge,  100  to  160  grm.,  according  to  the  proportion  of  the  sulphides. 

Nitre,  amount  calculated. 

Bicarb,  soda,  20  grm. 

Mix  thoroughly,  place  in  a thick  French  crucible,  which  should  not 
be  more  than  one-third  filled,  and  put  on  top  20  grm.  of  borax,  and 
a covering  of  common  salt.  The  fusion  is  made  slowly,  to  prevent  the 
assay  from  running  over,  and  is  kept  at  a strong  heat  for  an  hour.  The 


534 


SPECIAL  PART. 


[§  228. 


button  should  b6  malleable,  and  the  slag  should  give  no  odor  of  sul- 
phuretted hydrogen  when  treated  with  sulphuric  acid.  It  is  cupelled  as 
directed,  p.  530  (if  too  large  it  is  first  scorified),  and  the  gold  and  silver 
parted  as  directed  p.  532.] 


16.  Assay  of  Zinc  Ores. 

§ 228. 

Method  of  Schaffner,*  modified  by  C.  KuNZEL,f  as  employed  in  the 
Belgian  zinc-works  / described  by  C.  Groll.]; 

a.  Solution  of  the  ore  and  preparation  of  the  ammoniacal  solution. 

Powder  and  dry  the  ore. 

Take  0‘5  grm.  in  the  case  of  rich  ores,  1 grm.  in  the  case  of  poor  ores, 
transfer  to  a small  flask,  dissolve  in  hydrochloric  acid  with  addition  of 
some  nitric  acid  by  the  aid  of  heat,  expel  the  excess  of  acid  by  evapora- 
tion, add  some  water,  and  then  excess  of  ammonia.  Filter  into  a 
beaker,  and  wash  the  residue  with  lukewarm  water  and  ammonia,  till 
sulphide  of  ammonium  ceases  to  produce  a white  turbidity  in  the  wash- 
ings. The  oxide  of  zinc  remaining  in  the  hydrated  sesquioxide  of  iron 
is  disregarded.  Its  quantity,  according  to  Groll,  does  not  exceed 
03 — 0*5  per  cent.  This  statement  probably  has  reference  only  to  ores 
containing  relatively  little  iron ; where  much  iron  is  present  the  quan- 
tity of  zinc  left  behind  in  the  precipitate  may  be  not  inconsiderable. 
The  error  thus  arising  may  be  greatly  diminished  by  dissolving  the 
slightly  washed  iron  precipitate  in  hydrochloric  acid  and  adding  excess 
of  ammonia.  But  the  surer  mode  of  proceeding  is  to  add  to  the  origi- 
nal solution — after  evaporating  off  the  greater  part  of  the  free  acid  as 
above,  and  allowing  to  cool — dilute  carbonate  of  soda  nearly  to  neutral- 
ization, then  to  precipitate  the  sesquioxide  of  iron,  after  p.  202,  d , with 
acetate  of  soda,  boiling,  to  filter,  and  wash.  The  washings,  after  being 
concentrated  by  evaporation,  are  added  to  the  filtrate  and  the  whole 
is  then  mixed  with  ammonia,  till  the  first-formed  precipitate  is  redis- 
solved. 

If  the  ore  contains  manganese — provided  approximate  results  will 
suffice — digest  the  solution  of  the  ore  in  acids,  after  the  addition  of  ex- 
cess of  ammonia  and  water,  at  a gentle  heat  for  a long  time,  and  then 
filter  off,  with  the  iron  precipitate,  the  hydrated  protosesquioxide  of 
manganese  which  has  separated  from  the  action  of  the  air.  The  safer 
course — though  undoubtedly  less  simple — is,  after  separating  the  iron 
with  acetate  of  soda,  to  precipitate  the  manganese  by  passing  chlorine, 
as  directed  p.  357,  59,  or  by  adding  bromine  and  heating. 

If  lead  is  present,  it  is  separated  by  evaporating  the  aqua  regia  solu- 
tion with  sulphuric  acid,  taking  up  the  residue  with  water  and  filtering; 
then  proceed  as  directed. 

b.  Preparation  and  standardizing  of  the  sulphide  of  sodium  solu- 
tion. 

The  solution  of  sulphide  of  sodium  is  prepared  either  by  dissolving 
crystallized  sulphide  of  sodium  in  water  (about  100  grm.  to  1000 — 1200 

* Joum.  f.  prakfc.  Chem.  73,  410.  f Ibid.  88,  486. 

% Zeitschrift  f.  anal.  Chem.  1,  21. 


§ 228.] 


ANALYSIS  OF  ZINC  ORES. 


535 


water),  or  by  supersaturating  a solution  of  soda,  free  from  carbonic 
acid,  with  sulphuretted  hydrogen,  and  subsequently  heating  the  solution 
in  a llask  to  expel  the  excess  of  sulphuretted  hydrogen.  Whichever 
way  it  is  prepared,  the  solution  is  afterwards  diluted,  so  that  1 c.  c.  may 
precipitate  about  0*01  grm.  zinc.  Prepare  a solution  of  zinc,  by  dis- 
solving 10  grm.  chemically  pure  zinc  in  hydrochloric  acid,  or  44*122 
grm.  dry  crystallized  sulphate  of  zinc  in  water,  or  68*133  grm.  dry  crys- 
tallized sulphate  of  potash  and  zinc  in  water,  and  making  the  solution 
in  either  case  up  to  1 litre  with  water. 

Eaeh  c.  c.  of  this  solution  corresponds  to  0*01  grm.  zinc.  Now  mea- 
sure off  30 — 50  c.  c.  of  this  zinc  solution  into  a beaker,  add  ammonia 
till  the  precipitate  is  redissolved,  and  then  400 — 500  c.  c.  distilled  water. 
Pun  in  sulphide  of  sodium  as  long  as  a distinct  precipitate  continues  to 
be  formed,  then  stir  briskly,  remove  a drop  of  the  fluid  on  the  end  of  a 
rod  to  a porcelain  plate,  spread  it  out  so  that  it  may  cover  a somewhat 
large  surface,  and  place  in  the  middle  a drop  of  pure  dilute  solution  of 
chloride  of  nickel.  If  the  edge  of  the  drop  of  nickel  solution  remains 
blue  or  green,  proceed  with  the  addition  of  sulphide  of  sodium,  testing 
from  time  to  time,  till  at  last  a blackish  gray  coloration  appears  sur- 
rounding the  nickel  solution.  The  reaction  is  now  completed,  the  whole 
of  the  zinc  is  precipitated,  and  a slight  excess  of  sulphide  of  sodium  has 
been  added.  The  precise  depth  of  color  of  the  nickel  must  be  observed 
and  remembered,  as  it  will  have  to  serve  as  the  stopping  signal  in  future 
experiments.  To  make  sure  that  the  zinc  is  really  quite  precipitated, 
you  may  add  a few  tenths  of  a c.  c.  more  of  the  reagent,  and  test  again, 
of  course  the  color  of  the  nickel-drop  must  be  darker.  Note  the  num- 
ber of  c.  c.  used,  and  repeat  the  experiment,  running  in  at  once  the 
necessary  quantity  of  the  reagent,  less  1 c.  c.,  and  then  adding  0*2  c.  c. 
at  a time,  till  the  end-reaction  is  reached.  The  last  experiment  is  con- 
sidered the  more  correct  one.  The  sulphide  of  sodium  solution  must  be 
restandardized  before  each  new  series  of  analyses. 

c.  Determination  of  the  zinc  in  the  solution  of  the  ore. 

Proceed  in  the  same  way  with  the  ammoniacal  solution  prepared  in  a 
as  with  the  known  zinc  solution  in  b.  Here  also  repeat  the  experiment, 
the  second  time  running  in  at  once  the  required  number  of  c.  c.,  less  1, 
of  sulphide  of  sodium,  and  then  adding  0*2  c.  c.  at  a time,  till  the  end- 
reaction  makes  its  appearance.  The  second  result  is  considered  the  true 
one.  There  are  three  different  ways  in  which  this  repetition  of  the  ex- 
periment may  be  made.  You  may  either  weigh  out  at  the  first  two  por- 
tions of  the  zinc  ore,  or  you  may  weigh  out  double  the  quantity  required 
for  one  experiment,  make  the  ammoniacal  solution  up  to  1 litre  and  em- 
ploy ^ litre  for  each  experiment,  or  lastly,  having  reached  the  end-reac- 
tion in  the  first  experiment,  you  may  add  1 c.  c.  of  the  known  zinc  solu- 
tion, which  will  destroy  the  excess  of  sulphide  of  sodium,  and  then  run 
in  sulphide  of  sodium  in  portions  of  0*2  c.  c.,  till  the  end-reaction  is 
again  attained.  Of  course,  in  this  last  process  to  obtain  the  second  re- 
sult, you  deduct  from  the  whole  quantity  of  sulphide  of  sodium  used  the 
amount  of  the  same,  corresponding  to  1 c.  c.  of  the  zinc  solution. 

If  the  ore  contains  copper,  remove  it  from  the  acid  solution  by  sul- 
phuretted hydrogen,  evaporate  the  filtrate  with  nitric  acid,  dilute,  treat 
with  ammonia,  and  determine  the  zinc  as  above. 


536 


SPECIAL  PART. 


[§  229. 


17.  Analysis  of  Cast  Iron,  Steel,  and  Wrought  Iron. 

§ 229. 

Cast  iron,  one  of  the  most  important  products  of  metallurgic  indus- 
try, contains  a whole  series  of  elements,  mixed  in  greater  or  less 
proportion  with  the  iron,  or  combined  with  it.  Although  the  influence 
which  the  various  foreign  substances  mixed  with  the  iron  exercise  on 
the  quality  of  cast  iron  is  not  yet  accurately  known,  still  the  fact  that 
they  do  exercise  considerable  influence  on  the  quality  of  the  article  is 
beyond  doubt.  The  analysis  of  cast  iron  is  one  of  the  more  difficult 
problems  of  analytical  chemistry.  The  following  bodies  must  be  had 
regard  to  in  the  analysis — 

Iron,  carbon  combined  with  the  iron,  carbon  in  form  of  graphite , ni- 
trogen, silicon , phosphorus , sulphur , potassium,  sodium,  lithium,  calci- 
um, magnesium,  aluminium,  chromium,  titanium,  zinc,  manganese , 
cobalt,  nickel,  copper , tin,  arsenic,  antimony,  vanadium.  As  a general 
rule,  the  elements  in  italics  alone  are  quantitatively  determined. 

Steel  and  wrought  iron  are  analyzed  in  the  same  manner  as  cast  iron. 


1.  Determination  of  the  Carbon . 
a.  Determination  of  the  total  amount  of  Carbon. 

Method  of  Berzelius  (somewhat  modified.) 

Treat  about  3 grm.  of  the  cast  iron,  or  5 — 10  grm.  of  steel,  mode- 
rately comminuted,*  with  a neutral  concentrated  solution  of  chloride  of 
copper,  (made  by  mixing  hot  solutions  of  chloride  of  sodium  and  sulphate 
of  copper,  and  allowing  sulphate  of  soda  to  crystallize  out),  and  let  the 
mixture  stand  at  the  common  temperature  f with  occasional  stirring. 
In  5 or  6 hours,  or  as  soon  as  the  part  remaining  undissolved  presents  a 
mixed  mass  of  copper  and  separated  carbon,  &c.,  crumbling  under  pres- 
sure, add  hydrochloric  acid,  and,  if  necessary,  some  more  chloride  of 
copper,  and  digest  until  the  whole  of  the  copper  is  dissolved  to  subchlo- 
ride. At  this  stage  of  the  process  a gentle  heat  may  be  applied.  Filter 
through  a tube  of  the  form  shown  in  fig.  100,  the  narrow  part  of 
which  is  loosely  stopped  with  spongy  platinum  or  asbestos,  ignited  in  a 
current  of  moist  air.  Wash  well,  dry  thoroughly,  and  treat  the  entire 
contents  of  the  tube  either  as  directed  § 176  or  § 178.  After  emptying 


[*  Best  by  drilling1,  in  case  of  gray  pig  or  soft  steel.  White  pig  is  reduced  to 
powder  by  aid  of  the  steel  mortar.  ] 

f On  warming,  a small  quantity  of  gas  is  evolved,  which  contains  a trifling 
admixture  of  carbonetted  hydrogen.  [Sometimes  gas  escapes  at  ordinary  tem- 
peratures. In  that  case  a lump  of  ice  should  be  placed  in  the  vessel  at  first. 
After  an  hour  or  so  cooling  is  unnecessary.  ] 


§ 229.]  ANALYSIS  OF  CAST  IRON,  STEEL,  AND  WROUGHT  IRON. 


537 


the  tube,  rinse  with  a little  chromate  of  lead  or  oxide  of  copper  : if  the 
combustion  is  to  be  effected  in  a boat,  in  a current  of  oxygen  gas,  in 
order  that  the  incombustible  residue  may  be  examined,  rinse  with 
oxide  of  mercury. 

b.  Determination  of  the  Graphite. 

Treat  another  portion  of  the  cast  iron  with  moderately  con- 
centrated hydrochloric  acid,  at  a gentle  heat,  until  no  more 
gas  is  evolved;  filter  the  solution  through  asbestos  that  has 
been  ignited  in  a stream  of  moist  air  or  through  spongy  pla- 
tinum (comp.  «,),  wash  the  undissolved  residue,  first  with 
boiling  water,  then  with  solution  of  potassa,  after  this  with 
alcohol,  and  lastly  with  ether  (Max  Buchner)  ; * then  dry, 
and  burn  after  §176  or  §178.  Direct  weighing  is  not  advi- 
sable, as  the  graphite  generally  contains  silicon.  Deduct  the 
graphite  obtained  here  from  the  total  amount  of  carbon  found 
in  a ; the  difference  gives  the  combined  carbon. 


2.  Determination  of  the  Sulphur. 

The  safest  way  of  estimating  sulphur  in  cast  iron  is  the  following : — 
Put  about  10  grm.  of  the  substance,  in  the  finest  possible  state  of  divi- 
sion, into  the  flask  a (fig.  101),  insert  the  cork,f 
containing  the  funnel-tube  d c,  and  the  evolution 
tube  f ; the  funnel-tube  is  provided  with  a little 
mercury  at  i,  and  the  evolution  tube  is  connected 
with  two  U-tubes,  which  contain  a strongly  alka- 
line solution  of  lead.  Fill  the  funnel  d with  hy- 
drochloric acid,  and  suck  by  means  of  an  India- 
rubber  tube  at  the  exit  of  the  second  U-tube,  in 
which  a small  glass  tube  is  inserted ; the  acid 
will  thus  pass  into  the  flask.  Heat  the  flask, 
sucking  in  more  acid  from  time  to  time  as  just 
described,  till  complete  solution  of  the  iron  is 
effected ; then  connect  the  exit  of  the  second 
U-tube  with  an  aspirator,  and  draw  air  through 
the  apparatus  for  a long  time.  Collect  the  sul- 
phide of  lead  on  a small  filter,  fuse  it  cautiously 
with  a little  nitre  and  carbonate  of  soda,  soak  in 
water,  pass  carbonic  acid,  to  precipitate  traces  of 
dissolved  lead,  filter,  acidify  the  filtrate  with  hy- 
drochloric acid  and  precipitate  the  sulphuric  acid  with  chloride  of 
barium. 

To  make  quite  sure  that  you  have  left  no  sulphur  behind,  before 
throwing  away  the  contents  of  the  flask,  evaporate  the  solution  of  pro- 
tochloride of  iron,  to  drive  off  excess  of  hydrochloric  acid,  and  test  it 
with  chloride  of  barium ; also  fuse  the  undissolved  residue  with  nitre 


* Journ.  f.  prakt.  Chem.  72,  364. 

f If  a caoutchouc  stopper  were  used,  a little  sulphur  would  not  be  unlikely 
to  get  into  the  residue : the  caoutchouc  connections  must  be  desulphurized. 


538 


SPECIAL  PAET. 


and  carbonate  of  soda,  and  test  the  aqueous  extract  of  the  fused  mass  for 
sulphuric  acid.  As  a rule  the  residue  will  be  found  free  from  sulphur. 
But  if  any  sulphate  of  baryta  is  obtained  again  here,  it  may  be  collected 
on  the  same  filter  which  has  received  that  produced  from  the  sulphide 
of  lead. 

[3.  Estimation  of  Phosphorus. 

In  case  of  cast  iron,  when  the  amount  of  phosphorus  present  exceeds 

1 per  cent.,  2 grm.  suffice  for  a determination ; when  less  is  present  it  is 
best  to  take  at  least  3 grm.  Treat  with  aqua  regia  in  a tall  beaker 
covered  with  a watch-glass.  Digest  at  a moderate  temperature  2 or  3 
hours,  or  till  effervescence  ceases,  then  remove  the  cover  and  evaporate 
to  dryness,  as  in  the  ordinary  way  of  separating  silica,  with  addition  of 
nitric  acid,  if  need  be,  to  remove  chlorine.  A temperature  a few  de- 
grees above  that  attainable  with  the  water-bath  may  be  used  to  hasten 
this  operation.  But  if  too  high  heat  is  used,  oxide  of  iron  will  remain 
undissolved  on  subsequent  treatment  with  nitric  acid  ; moreover,  pyro- 
phosphate may  be  formed  at  a temperature  below  150°  C.  After  the  re- 
sidue has  been  dried  sufficiently  to  make  the  silica  insoluble,  digest  with 
nitric  acid  till  the  iron  is  dissolved.  Separate  the  residue  by  filtering, 
and  reserve  it  for  determ inatioh  of  silicon.  To  the  filtrate  add  100 
c.  c.  of  molybdic  acid  solution.  If  after  the  addition  of  this  reagent  the 
solution  amounts  to  less  than  350  to  400  c.  c.,  dilute  to  that  volume. 

Place  for  24  hours  in  a warm  situation  where  the  temperature  does 
not  rise  above  40°  C.  Wash  the  precipitate  with  the  molybdic  solution, 
diluted  with  an  equal  volume  of  water,  letting  the  washings  run  into  the 
filtrate.  Then  allow  the  filtrate  to  stand  24  hours  or  more  in  a warm 
place,  and  collect  any  appreciable  amount  of  phospho-molybdate  that 
may  separate.  Dissolve  and  reprecipitate  according  to  p.  271. 

Steel  (3 — 10)  grm.  may  be  dissolved  in  nitric  acid  of  1*20  sp.  gr., 
and  evaporation  to  dryness  may  be  omitted  when  silicon  is  not  to  be 
estimated.] 

[4.  Estimation  of  Silicon. 

The  residue  from  the  solution  used  for  determining  phosphorus  may 
be  used  for  determining  silicon.  Ignite  it  without  separation  from  the 
filter  until  the  graphite  is  partially  burned  away.  Puse  with  car- 
bonate of  soda  mixed  with  a little  nitrate  of  potash,  sufficient  to  effect 
complete  combustion  of  the  carbon  still  present.  Treat  the  fused  mass 
first  with  boiling  water,  in  which  it  readily  dissolves,  except  some  silica 
in  light  flocculent  form,  and  traces  of  metallic  oxides.  Acidify  with 
hydrochloric  acid,  or  nitric  acid,  in  case  the  solution  is  to  be  in  contact 
with  platinum,  and  separate  silica  as  usual.  When  the  quantity  of  silica 
is  not  over  1 per  cent.,  these  operations  may  be  most  conveniently  per- 
formed in  a large  platinum  crucible  without  transferring  the  substance 
to  any  other  vessel.] 

[5.  Estimation  of  Manganese  and  Cobalt . 

2 grm.  is  as  large  a quantity  as  can  conveniently  be  treated  by  the 
method  here  proposed,  and  will  in  most  cases  suffice.  Where  less  than 

2 per  cent,  is  present,  and  great  accuracy  is  required,  it  is  necessary 
perhaps  to  take  more.  Of  spiegeleisen  1 to  \ grm.  suffices.  Prepare  a 


229.]  ANALYSIS  OF  CAST  IRON,  STEEL,  AND  WROUGHT  IRON. 


539 


solution  of  the  iron  in  the  same  manner  as  for  phosphorus  (3).  A higher 
temperature  may,  however,  be  used  to  make  silica  insoluble,  and  hydro- 
chloric acid  may  be  used  for  redissolving.  Filter  from  the  residue  of 
carbon  and  silica  into  a large  flask.  When  the  solution  is  cold,  add  car- 
bonate of  soda  as  long  as  the  precipitate  formed  by  it  can  be  redissolv- 
ed by  shaking  and  letting  stand  a few  minutes.  Next  add  12  to  15  c.  c. 
strong  acetic  acid,  and  the  same  volume  of  a saturated  solution  of  ace- 
tate of  soda.  Dilute,  now,  the  solution  to  about  1 litre,  and  precipi- 
tate iron  by  boiling.  Filter  and  wash  without  decantation,  as  long  as 
the  water  passes  freely  through  the  mass  upon  the  filter.  When  the 
washing  becomes  tedious,  on  account  of  slow  passage  of  water  through 
the  filter,  rinse  the  precipitate  from  the  filter  into  a dish  with  a jet  of 
water,  and  boil  with  a moderate  amount  of  water  with  addition  of  a 
little  acetate  of  soda,  stirring  with  a glass  rod  as  long  as  any  coherent 
ldmps  of  precipitate  remain.  Bring  the  precipitate  back  again  upon 
the  filter  and  complete  the  washing.  Concentrate  the  filtrate  and  washings 
to  about  300  c.  c.  (or  less  if  too  much  saline  matter  is  not  present).  A 
little  iron  is  usually  present  in  this  filtrate  ; sometimes  it  is  partially 
deposited  during  the  evaporation.  In  order  to  separate  the  manganese 
from  this,  and  from  the  large  quantity  of  saline  matter  in  the  liquid, 
precipitate  next  all  the  metallic  oxides  present  by  gradually  adding  car- 
bonate of  soda  to  the  boiling  solution  as  long  as  a precipitate  is  formed, 
and  adding  at  the  close  a few  drops  of  caustic  soda.  Filter,  wash 
the  precipitate  slightly,  dissolve  it  on  the  filter  with  hydrochloric  acid, 
and  separate  the  small  quantity  of  iron  in  the  new  solution  with  ace- 
tate of  soda.  For  this  purpose,  when,  as  usually  is  the  case,  but  little 
iron  is  present,  the  solution  need  occupy  but  a small  volume  (100  c.  c.). 
Add  carbonate  of  soda  as  long  as  no  permanent  precipitate  is  formed, 
then  2 or  3 c.  c.  of  the  acetate  of  soda  solution,  and  heat*  gradually  to 
boiling.  Sometimes  when  this  solution  is  moderately  warmed,  and  car- 
bonic acid  has  mostly  escaped,  but  before  the  temperature  is  high  enough 
to  precipitate  the  iron,  the  solution  will  become  turbid  with  a finely 
divided  white  precipitate.  If  this  happens,  add  acetic  acid  till  it  dis- 
solves, and  then  raise  the  heat  to  boiling.  Filter  from  the  precipitated 
iron,  and  precipitate  manganese  in  the  filtrate  with  bromine  (see  § 
223,2).  When  no  great  accuracy  is  required,  this  precipitate  may  be 
washed,  ignited,  and  weighed  as  protosesquioxide  of  manganese,  and 
metallic  manganese  calculated  from  it.  It  may,  however,  contain  cobalt, 
which  is  often  present  in  pig  iron,  and  possibly  traces  of  copper. 

To  detect  the  presence  of  cobalt , dissolve  the  weighed  oxide  of  man- 
ganese in  a few  drops  of  HC1,  heat  till  the  brown  color  imparted  by 
the  manganese  disappears.  A comparatively  small  amount  of  cobalt 
will  now  give  the  solution,  while  hot  and  concentrated,  a bright  green 
color  that  disappears  on  diluting  with  cold  water.  Evaporate  the  solu- 
tion till  free  acid  is  expelled,  dissolve  in  a small  quantity  of  water, 
add  acetate  of  soda  and  a drop  of  acetic  acid,  heat  to  boiling  and 
transmit  HS,  which  will  precipitate  the  cobalt.  Collect  the  precipitate 
on  a filter,  wash  rapidly  with  water  containing  HS.  Testing  this  pre- 
cipitate with  a blowpipe  will  further  confirm  its  nature.  If  it  be 
judged  from  this  examination  that  cobalt  is  present  in  any  sensible 
quantity,  evaporate  the  filtrate  last  obtained  till  HS  is  expelled,  and 
precipitate  manganese  again  with  carbonate  of  soda,  and  weigh  it  as 
protosesquioxide. 


SPECIAL  PART. 


540 

For  most  practical  purposes  sufficiently  good  results  may  be  usually 
obtained  in  the  analysis  of  spiegeleisen , e.  g.,  by  separating  iron  from  a 
solution  of  0'5 — 0*7  grm.  as  above  described,  precipitating  the  con- 
centrated filtrate  directly  by  means  of  phosphate  of  soda  and  weighing 
the  manganese  as  pyrophosphate.  See  p.  185.] 

5.  Determination  in  one  portion  of  the  total  amounts  of  silicon , 
iron , manganese , zinc,  cobalt , nickel , alumina , titanic  acid , 
alkaline  earths  and  alkalies. 

Dissolve  about  10  grm.  of  the  cast  iron  in  a capacious  platinum  dish,* 
in  moderately  dilute  hydrochloric  acid,  evaporate  with  a few  drops  of 
dilute  sulphuric  acid  on  the  water-bath  to  dryness,  till  the  mass  ceases 
to  smell  of  hydrochloric  acid,  moisten  with  hydrochloric  acid,  heat,  add 
water,  filter,  wash  and  dry  the  precipitate.  Let  us  call  it  a.  Heat  the 
solution  in  a porcelain  dish  with  nitric  acid,  dilute  copiously  and  precipi- 
tate the  sesquioxide  of  iron,  &c.,  by  nearly  saturating  with  carbonate  of 
ammonia  and  boiling,  after  p.  362,  69.  Wash  and  dry  the  precipitate; 
call  it  b. 

Mix  the  filtrate  from  b with  ammonia  in  slight  excess,  heat  till  the 
excess  of  ammonia  is  almost  expelled,  filter,  dissolve  in  hydrochloric  acid 
and  reprecipitate  in  the  same  manner.  Filter,  wash  and  dry  the  pre- 
cipitate ; call  it  c. 

Acidify  the  filtrate  from  c with  hydrochloric  acid,  concentrate  in  a 
porcelain  dish,  transfer  to  a flask,  add  ammonia  and  sulphide  of  ammo- 
nium and  proceed  generally  as  directed  p.  184,  c.  After  24  hours,  filter 
the  precipitate  (d)  off,  wash  it  with  water  containing  sulphide  of  ammo- 
nium, spread  the  filter  on  a glass  plate,  rinse  the  precipitate  into  a flask, 
treat  it  with  acetic  acid,  cork  and  set  aside. 

Evaporate  the  filtrate  from  c?ina  platinum  dish  to  dryness,  expel  the 
ammonia  salts  at  the  lowest  temperature  possible,  and  in  the  residue 
determine  the  alkaline  earths  and  alkalies.  For  this  purpose  precipitate 
the  lime  by  pure  oxalate  of  ammonia  repeating  the  precipitation  accord- 
ing to  29,  and  from  the  filtrate  separate  magnesia  according  to  16.  The 
alkalies  are  weighed  as  chlorides  and  potassa  is  finally  estimated  by  1, 

The  residue  a contains  the  whole  of  the  bodies  insoluble  or  difficultly 
soluble  in  hydrochloric  acid.  The  following  substances  may  be  present 
besides  carbon  and  silica,  viz.,  phosphide  of  iron,  chromium-iron,  vana- 
dium-iron, arsenide  of  iron,  carbide  of  iron,  silicon,  molybdenum,  &c., 
and  also  slag  in  a more  or  less  altered  condition.  Titanic  acid  and  sul- 
phate of  baryta  may  also  be  here  present.  Fuse  with  carbonate  of  soda 
and  potash,  and  a little  nitre,  separate  the  silica  as  usual,  by  evaporating 
with  hydrochloric  acid  and  two  drops  of  dilute  sulphuric  acid,  weigh  it 
and  see  whether  it  is  pure  (comp.  p.  300) ; the  impurities  most  likely  to 
be  present  are  sulphate  of  baryta  and  titanic  acid.  The  silicic  acid  may 
have  been  partially  formed  from  silicon,  and  partially  present  as  such  in 
the  slag.  In  the  filtrate  from  the  silicic  acid  separate  what  is  separable 
by  ammonia  by  double  precipitation,  filter  off  the  precipitate  (c  ),  then 
precipitate  with  sulphide  of  ammonium,  filter  off  the  precipitate  ( d',  to 
be  treated  as  d)  and  finally  test  the  filtrate  for  alkaline  earths,  any  small 
quantities  of  which  found  can  then  be  weighed  with  the  somewhat  larger 
amount  obtained  above. 


* If  glass  or  porcelain  be  used,  the  estimations  of  the  silicon  and  aluminium 
cannot  be  considered  as  absolutely  exact. 


§ 2 2D.]  ANALYSIS  OF  CAST  IRON,  STEEL,  AND  WROUGHT  IRON.  541 


The  precipitates  5,  c and  c contain  the  whole  of  the  sesquioxide  of 
iron  and  alumina,  also  that  part  of  the  titanic  acid  which  has  passed 
into  solution.  Transfer  the  mixed  ignited  precipitates  to  several  plati- 
num or  porcelain  boats,  put  these  in  a glass  tube  and  ignite  in  pure  hy- 
drogen, till  no  more  steam  issues.  Treat  the  boats  and  their  contents 
with  very  dilute  nitric  acid  (1  of  acid  to  30 — 40  of  water)  to  dissolve 
the  iron,  make  the  solution  up  to  1000  c.  c.  and  determine  the  iron  in  an 
aliquot  part  by  oxidation  and  precipitation  with  ammonia.*  Fuse  the 
residue,  which  was  insoluble  in  the  very  dilute  nitric  acid,  with  bisul- 
phate of  potash,  take  up  with  cold  water,  filter  off  any  residual  silica, 
collect  and  weigh  it  and  add  the  weight  to  that  found  above ; pass  sul- 
phuretted hydrogen,  endeavor  to  precipitate  any  titanic  acid  that  may 
be  present  by  boiling  and  passing  a stream  of  carbonic  acid,  boil  the  fil- 
trate or  the  clear  solution  with  nitric  acid,  precipitate  the  alumina  with 
ammonia,  and  separate  it  from  the  small  quantity  of  sesquioxide  of  iron 
that  may  possibly  be  present  by  the  method  given  p.  52 1 (precipitate.  II). 
In  this,  as  in  that  case,  regard  must  be  paid  to  phosphoric  acid,  as  its 
presence  would  give  fictitious  weight  to  the  alumina.  If  chromium  were 
present,  its  oxide  would  likewise  have  to  be  separated  and  determined  in 
this  precipitate. 

The  precipitates  d and  d'  have  given  up  to  the  acetic  acid  almost  the 
whole  of  their  sulphide  of  manganese.  Filter  off  the  solution,  suspend 
the  residue  in  sulphuretted  hydrogen  water,  and  add  some  hydrochloric 
acid.  Under  these  circumstances,  the  sulphide  of  zinc  and  any  residual 
sulphide  of  manganese  are  dissolved,  while  the  sulphide  of  copper  (which 
is  not  here  estimated),  sulphide  of  nickel,  and  sulphide  of  cobalt  are  left 
behind.  Evaporate  the  hydrochloric  acid  solution  to  a small  bulk,  boil 
with  excess  of  solution  of  soda,  precipitate  any  zinc  from  the  solution 
by  sulphuretted  hydrogen,  dissolve  any  separated  hydrate  of  protoses- 
quioxide  of  manganese  in  hydrochloric  acid,  add  the  solution  to  the 
acetic  acid  solution,  and  determine  the  manganese  in  the  mixture. 
Incinerate  the  filter,  containing  the  sulphides  of  copper,  nickel  and 
cobalt,  dissolve  in  hydrochloric  acid,  precipitate  with  sulphuretted  hy- 
drogen, and  in  the  filtrate  thus  freed  from  copper  estimate  the  nickel 
and  cobalt. 

6.  Determination  in  one  portion  of  the  metals  of  Groups  V.  and 
VI.  and  of  the  phosphorus. 

Treat  10  grm.  of  the  cast  iron  in  the  finest  possible  state  of  division 
with  a previously  heated  mixture  of  1 volume  of  nitric  acid  and  3 vol- 
umes of  hydrochloric  acid  (both  acids  must  be  pure  and  strong)  in  a 
very  capacious,  long-necked,  obliquely  placed  flask  at  a gentle  heat. 
When  all  visible  action  has  ceased,  decant  the  solution  and  treat  the 
residue  with  a fresh  portion  of  aqua  regia.f  Mix  the  solutions,  dilute 
copiously  and  treat  in  a large  flask  with  sulphuretted  hydrogen,  at  first 
in  the  cold,  then  at  70°.  I may  here  observe  that  the  solution  usually 


* It  is  not  advisable  to  determine  the  iron  in  a separately  weighed  smaller 
quantity,  unless  the  sample  to  be  examined  is  perfectly  homogeneous. 

f Instead  of  aqua  regia,  bromine  and  water  may  be  used.  The  solution  goes 
on  rapidly,  at  first  almost  violently,  if  the  bromine  is  in  excess  and  the  mixture 
is  digested  at  20° — 30°.  Toward  the  end  assist  the  action  by  the  heat  of  a water- 
bath  (J.  Nickles).  If  this  method  is  employed,  I should  still  recommend  that  the 
residue  be  treated  with  aqua  regia. 


542 


SPECIAL  PART. 


[§  229. 


retains  a brownish  tint  from  dissolved  organic  substances,  even  after  the 
sesquichloride  of  iron  is  reduced.  Allow  the  fluid  (saturated  with  sul- 
phuretted hydrogen)  to  settle  for  24  hours,  filter,  dry  the  precipitate, 
which  consists  principally  of  sulphur,  and  extract  it  with  warm  bisul- 
phide of  carbon.  There  usually  remains  a small  black  residue,  which 
often  contains,  besides  sulphide  of  copper,  a little  sulphide  of  arsenic 
and  sulphide  of  antimony.  Separate  these,  or  generally  the  metals 
present  of  the  fifth  and  sixth  groups,  according  to  the  methods  given  in 
Section  V. 

Free  the  filtrate  from  the  sulphuretted  hydrogen  precipitate  from  the 
excess  of  the  gas  by  transmission  of  carbonic  acid,  add  a little  pure 
sesquichloride  of  iron,  nearly  neutralize  the  solution  with  pure  carbon- 
ate of  soda  and  precipitate  with  carbonate  of  baryta  in  a closed  flask. 
Treat  the  precipitate,  which  contains  the  whole  of  the  phosphoric  acid 
(produced  by  the  oxidation  of  the  phosphorus  compounds),  with  hydro- 
chloric acid,  precipitate  the  baryta  with  sulphuric  acid,  filter,  evaporate 
to  small  bulk,  precipitate  the  phosphoric  acid  with  solution  of  molybde- 
num and  determine  it  after  p.  271,  j8. 

As  a portion  of  the  phosphide  of  iron  may  have  escaped  oxidation  by 
the  aqua  regia,  fuse  the  residue  insoluble  therein  with  carbonate  of  soda 
and  nitre,  and  test  the  aqueous  solution  of  the  fused  mass  likewise  for 
phosphoric  acid. 


18.  ANALYSIS  OF  MANURES. 


§ 231. 

I speak  here  simply  of  the  manures  which  owe  their  origin  to  the 
urine,  excrements,  blood,  bones,  &c.,  of  animals,  or  are  prepared  by  the 
decomposition  of  apatite,  &c.,  by  acids.  The  examination  of  manures 
has  chiefly  a practical  object,  and  demands  accordingly  simple  methods. 
The  value  of  a manure  depends  upon  the  nature  and  condition  of  its 
constituents.  The  following  constituents  are  the  most  important : — or- 
ganic matters  (characterized  by  their  carbon  and  nitrogen),  ammonia 
salts,  nitrates,  phosphates,  sulphates,  and  chlorides  with  alkaline  and 
alkaline  earthy  bases  (potassa,  soda,  lime,  magnesia).  To  these  sub- 
stances we  know  the  efficacy  of  a manure  is  owing,  but  as  to  the  condi- 
tion in  which  they  exercise  the  most  favorable  action,  our  views  are 
much  less  clear ; indeed,  it  is  obvious  that  a universally  applicable  and 
valid  rule  cannot  well  be  laid  down  in  this  respect ; since  the  agricul- 
turist sometimes  wishes  a manure  containing  most  of  its  constituents  in 
a state  of  solution,  which  will  accordingly  exercise  a speedy  fertilizing 
action,  and  sometimes  one  which  will  only  gradually  supply  the  soil  with 
the  substances  required  by  the  plants.  As  regards  the  insoluble  mate- 
rials of  manures,  it  may  be  safely  asserted  that  their  value  advances  in 
proportion  as  their  degree  of  division  and  solubility  increases. 

I will  here  give,  1,  the  outlines  of  a general  method  of  examination 
applicable  to  almost  all  kinds  of  manures ; 2,  methods  of  valuing  guano 
and  manures  prepared  from  bones,  apatite,  &c. 

A.  General  Process. 

§ 232. 

Mix  the  manure  uniformly  by  chopping  and  grinding,  then  weigh  off* 
successively  ther  several  portions  required  for  the  various  estimations. 

1.  Determination  of  the  Water. — Dry  10  grm.  at  125°,  and  deter- 
mine the  loss  of  weight  (§  29).  (It  is  rarely  necessary  to  make  a cor- 
rection on  account  of  the  carbonate  of  ammonia  which  escapes  with  the 
water.*) 

2.  Total  Amount  of  fixed  Constituents. — Incinerate,  at  a gentle  heat, 
a weighed  portion  of  the  residue  left  in  1,  in  a thin  porcelain  dish; 
moisten  the  ash  with  a solution  of  carbonate  of  ammonia,  dry,  ignite 
gently,  and  weigh. 

* To  do  so,  dry  the  manure  in  a boat  inserted  in  a tube  ; the  tube  is  heated  to 
100°  in  the  water-  or  air-bath,  a current  of  air  being  transmitted  through  it,  by 
means  of  an  aspirator : the  air  enters  through  concentrated  sulphuric  acid,  and 
makes  its  exit  through  two  U- tubes  containing  standard  sulphuric  acid.  After 
drying,  the  quantity  of  ammonia  expelled,  which  has  combined  with  the  standard 
acid,  is  determined  (§  99,  3). 


544 


SPECIAL  PART. 


3.  Constituents  soluble  in  Water , and  insoluble  in  Water. — Digest  10 
grm.  of  the  fresh  manure  with  about  300  c.  c.  water,  collect  the  residue 
on  a weighed  filter,  wash,  dry  at  125°,  and  weigh.  The  weight  found 
expresses  the  total  quantity  of  the  substances  insoluble  in  waiter,  and 
the  difference — after  deducting  the  water  found  in  1 — gives  the  amount 
of  the  soluble  constituents.  Incinerate  now  the  insoluble  residue,  treat 
with  carbonate  of  ammonia,  as  in  2,  and  weigh  ; the  weight  expresses 
the  total  amount  of  the  fixed  constituents  contained  in  the  insoluble 
part,  and  the  difference  between  this  and  the  ash  in  2 gives  the  total 
amount  of  fixed  constituents  contained  in  the  soluble  part. 

4.  Fixed  Constituents  singly. — [Obtain  3 — 5 grm.  of  ash  according  to  2. 
Treat  2 grm.  with  hot  dilute  hydrochloric  acid  until  only  insoluble  mat- 
ters (sand,  clay,  and  charcoal)  remain,  which  filter  off,  wash,  igni.te,  and 
weigh.  The  filtrate  and  washings  are  brought  to  the  bulk  of  200  c.  c., 
mixed,  and  divided  into  four  equal  parts. 

a.  To  50  c.  c.  add  ammonia  until  a slight  permanent  precipitate  is 
formed,  then  enough  hydrochloric  acid  to  dissolve  this  precipitate,  heat 
to  boiling,  and  add  acetate  of  soda  as  long  as  a precipitate  forms,  wash, 
ignite,  and  weigh.  Two  cases  may  here  present  themselves. 

a.  If  the  precipitate  before  ignition  were  red  it  contains  all  the  iron, 
alumina,  and  phosphoric  acid.  In  this  case  dissolve  it  in  concentrated 
hydrochloric  acid  with  cautious  addition  of  sulphuric  acid,  towards  the 
last,  finally  evaporate  oft'  the  hydrochloric  acid  (or  fuse  with  carbonate 
of  soda  and  dissolve  in  sulphuric  acid)  and  determine  the  sesquioxide  of 
iron  volumetrically  (p.  203).  Afterwards  in  the  same  liquid  determine 
phosphoric  acid  by  molybdic  solution  (p.  271).  Calculate  alumina  by 
difference.  In  the  filtrate  from  the  acetate  of  soda  precipitate,  deter- 
mine lime  as  oxalate,  and  afterwards  magnesia  as  pyrophosphate,  ac- 
cording to  29,  P-  349. 

/?.  If  the  precipitate  before  ignition  were  nearly  white,  it  contains  all 
the  iron  and  alumina  and  a portion  of  the  phosphoric  acid.  It  may  be 
analyzed  as  just  described,  or,  if  very  small  in  quantity,  half  of  it  may 
be  reckoned  as  phosphoric  acid  (see  page  141).  From  the  filtrate  con- 
taining free  acetic  acid,  lime  is  precipitated  as  oxalate  (30,  p.  350),  the 
second  filtrate  is  then  neutralized  by  ammonia,  when  all  the  magnesia 
and  a portion  of  phosphoric  acid  go  down  as  ammonio-phosphate  of 
magnesia;  the  third  filtrate  is  treated  with  magnesia-mixture  to  separate 
the  rest  of  the  phosphoric  acid. 

b.  To  another  50  c.  c.  add  hot  concentrated  solution  of  caustic  baryta 
in  slight  excess,  boil,  and  filter.  The  filtrate  (and  washings)  containing 
only  alkali  chlorides  and  chlorides  of  barium  and  calcium,  is  treated  hot 
with  solution  of  carbonate  of  ammonia  and  some  caustic  ammonia,  fil- 
tered from  carbonates  of  baryta  and  lime,  the  liquid  evaporated  and 
ignited  to  expel  ammonia-salts,  and  this  process  repeated,  if  need  be, 
until  pure  alkali  chlorides  are  obtained  (see  p.  303,  last  paragraph),  in 
which  the  potassa  and  soda  are  determined  according  to  1,  p.  339,  or  5, 
p.  342. 

c.  In  a third  portion  of  50  c.  c.,  estimate  sulphuric  acid  by  precipita- 
tion with  chloride  of  barium. 

The  fourth  50  c.  c.  is  reserved  for  use  in  case  of  accidents.] 

d.  Determine  the  carbonic  acid  in  another  portion  of  the  ash,  as 
directed  p.  291,  cc,  or  p.  293,  e.  Filter  the  contents  of  the  flask  (in 
which  the  solution  has  been  effected  with  the  aid  of  dilute  nitric  acid), 


233.] 


ANALYSIS  OF  GUANO. 


545 


and  precipitate  the  chlorine  with  solution  of  nitrate  of  silver,  as  directed 

§ 141,  L,  «. 

5.  Total  amount  of  Ammonia. — Treat  a weighed  portion  of  the  ma- 
nure by  Schlosing’s  method  (p.  158,  6*). 

6.  Total  amount  of  Nitrogen. — Moisten  a weighed  portion  of  the 
manure  with  a dilute  solution  of  oxalic  acid  in  sufficient  quantity  to  im- 
part a feebly  acid  reaction ; dry,  and  determine  the  nitrogen,  in  the  en- 
tire mass  or  in  a weighed  portion,  after  § 185.  If  you  deduct  from  the 
total  amount  of  nitrogen  so  found  the  quantity  corresponding  to  the 
ammonia  and  the  nitric  acid,  the  difference  shows  the  quantity  of  nitro- 
gen contained  in  the  organic  substances.  It  is  generally  sufficient,  how- 
ever, to  know  the  total  amount  of  the  nitrogen. 

7.  Total  amount  of  Carbon. — Treat  a portion  of  the  dried  residue  of 
1 by  the  process  of  organic  analysis  (§  189).  If  the  dried  manure  con- 
tains carbonates,  determine  the  carbonic  acid  in  a separate  portion,  and 
deduct  the  result  from  the  total  amount  obtained  by  the  organic  analy- 
sis ; the  difference  shows  the  quantity  of  carbonic  acid  formed  in  the 
latter  process  by  the  carbon  of  the  organic  substances. 

8.  Nitric  Acid. — Treat  a weighed  portion  of  the  manure  with  water, 
and  evaporate  the  solution,  with  addition  of  pure  carbonate  of  soda  to 
distinct  alkaline  reaction;  filter  after  some  time,  then  evaporate  the  fil- 
trate to  a small  bulk,  and  determine  in  fractional  parts  of  it  the  nitric 
acid.  As  the  solution  will  scarcely  ever  be  free  from  organic  matter, 
employ  Schlosing’s  method  (p.  331). 

B.  Analysis  of  Guano. 

§ 233. 

Guano  consists  of  the  excrements  of  sea-fowls,  more  or  less  altered. 
It  not  only  varies  very  considerably  in  quality  in  the  different  islands 
from  which  our  supplies  are  derived,  but  is  often  also  fraudulently  adul- 
terated with  earth,  brick-dust,  carbonate  of  lime,  and  other  matters. 

The  guano  is  mixed  as  uniformly  as  possible,  and  that  which  is  in- 
tended for  analysis  is  put  into  a stoppered  bottle. 

1.  Determination  of  the  Water. — This  is  effected  exactly  as  on  p.  543 
(1).  In  exact  analyses  the  carbonate  of  ammonia  must  not  be  over- 
looked— (see  note).  Genuine  guano  loses  from  7 to  18  per  cent. 

2.  Total  amount  of  fixed  Constituents. — Incinerate  a weighed  portion 
in  a porcelain  or  platinum  crucible  placed  in  a slanting  position,  and 
weigh  the  ash.  Good  guano  leaves  from  30  to  33  per  cent,  of  ash,  guano 
of  bad  quality  from  60  to  80  per  cent.,  and  a wilfully  adulterated  arti- 
cle often  even  more.  The  ash  of  genuine  guano  is  white  or  gray.  A 
yellow  or  reddish  color  indicates  adulteration  with  loam,  sand,  or  earth. 
In  the  first  stage  of  the  decomposition  by  heat,  good  guano  emits  a 
strong  ammoniacal  odor  and  white  fumes. 

3.  Constituents  soluble  in  Water , and  insoluble  in  Water. \ — Heat  10 


* Small  quantities  of  ammonia  are  determined  with  decinormol  sulphuric  acid. 
\ It  must  be  mentioned  that  the  quality  and  quantity  of  the  constituents  solu- 
ble in  water  are  by  no  means  constant  for  the  same  guano.  Liebig  (Anna!  d. 
Chem.  u.  Pharm.,  119,  13)  has  shown  that  the  kind  of  salts  which  pass  into  solu- 
tion varies  according  to  whether  one  filters  the  solution  off  immediately  or  after 
35 


546 


SPECIAL  PART. 


[§  233. 


grm.  guano  with  about  200  c.  c.  water,  collect  the  residue  on  a.  weighed 
filter  without  delay,  and  wash  it  with  hot  water,  until  the  water  running 
off  looks  no  longer  yellowish  and  leaves  no  residue  wdien  evaporated 
upon  platinum  foil ; dry  the  residue,  and  weigh.  Deduct  the  sum  of 
the  water  and  the  residue  from  the  weight  of  the  guano  ; the  remainder 
expresses  the  amount  of  the  soluble  constituents.  Incinerate  the  resi- 
due and  weigh  the  ash ; the  difference  shows  the  amount  of  the  fixed 
soluble  salts.  With  very  superior  sorts  of  guano,  the  residue  insoluble 
in  water  amounts  to  from  50  to  55  per  cent.,  with  inferior  sorts,  to  from 
80  to  90  per  cent.  The  brown-colored  aqueous  solution  of  genuine 
guano  evolves  ammonia  upon  evaporation,  emits  a urinous  smell,  and 
leaves  a brown  saline  mass,  consisting  chiefly  of  sulphates  of  soda  and 
potassa,  chloride  of  ammonium,  oxalate  and  phosphate  of  ammonia. 

4.  Fixed  Constituents  singly. — As  in  § 232. 

5.  Total  amount  of  Ammonia.  u 

6.  Total  amount  of  Nitrogen.  a 

7.  Total  amount  of  Carbon.  “ 

8.  Nitric  Acid.  “ 

9.  Carbonic  Acid,. — Employ  one  of  the  methods  § 139,  II.  Genuine 
guano  contains  only  a small  proportion  of  carbonates.  If,  therefore,  a 
guano  effervesces  strongly  when  moistened  with  dilute  hydrochloric 
acid,  this  may  be  regarded  as  a proof  of  adulteration  with  carbonate  of 
lime. 

10.  Uric  Acid. — If  it  is  wished  to  ascertain  the  quantity  of  uric  acid 
which  a guano  contains,  treat  thq  part  insoluble  in  water  with  a weak 
solution  of  soda  at  a gentle  heat,  filter,  and  acidify  the  filtrate  with  hy- 
drochloric acid,  to  precipitate  the  uric  acid.  Collect  on  a weighed  filter, 
wash  cautiously  with  the  least  possible  quantity  of  cold  water,  dry,  and 
weigh. 

11.  Oxalic  Acid. — As  appears  from  the  note  to  3,  the  oxalate  of 
ammonia  in  guano  plays  an  important  part  with  respect  to  the  solution 
of  the  phosphate  of  lime.  It  is,  therefore,  frequently  a matter  of  inter- 
est to  determine  the  oxalic  acid.  This  is  best  done  in  a separate  por- 
tion after  § 137,  d,  p.  A little  dilute  sulphuric  acid  is  first  made  to  act 
upon  the  guano,  till  all  the  carbonic  acid  is  expelled,  the  sulphuric  acid 
is  then  neutralized  with  solution  of  soda  free  from  carbonic  acid,  the 
manganese  is  added  and  the  decomposition  is  effected  with  dilute  sul- 
phuric acid.  I prefer  to  conduct  the  decomposition  in  the  apparatus 
figured  p.  294,  collecting  the  carbonic  acid  in  a weighed  soda-lime 
tube. 

As  the  manuring  value  of  a sample  of  guano  may  be  estimated,  with 
sufficient  accuracy,  from  the  phosphoric  acid  and  nitrogen  which  it  con- 


some  time.  In  the  first  case,  the  solution  contains  much  oxalate  and  little  phos- 
phate, together  with  some  sulphate  of  ammonia  ; in  the  second  case,  the  oxalate 
of  ammonia  is  more  or  less  completely  replaced  by  phosphate  of  ammonia,  the 
oxalic  acid  having-  combined  with  lime  in  the  residue.  The  cause  of  this  deport- 
ment is  that  phosphate  of  lime,  although  when  in  contact  with  oxalate  of  ammo- 
nia and  water  alone  it  scarcely  suffers  any  change,  is  very  soon  converted  into 
oxalate  of  lime,  with  formation  of  phosphate  of  ammonia,  when  sulphate  of  am- 
monia (or  chloride  of  ammonium)  is  also  present.  The  sulphate  of  ammonia 
renders  the  phosphate  of  lime  somewhat  soluble,  the  dissolved  part  is  at  once 
precipitated  by  the  oxalic  acid,  and  the  sulphate  of  ammonia  is  thus  enabled  tc 
act  afresh  upon  the  phosphate  of  lime. 


ANALYSIS  OF  BONE  DUST. 


547 


§ 234.] 

tains,  the  analysis  is  often  considerably  shortened,  and  confined  to  the 
following  processes  : — 

a.  Determination  of  T Voter  (see  1). 

b.  Determination  of  Ash  (see  2). 

c.  Determination  of  Phosphoric  Acid. — Mix  1 part  (1  or  2 grm.)  of 
the  sample  of  guano  with  1 part  of  carbonate  of  soda  and  1 part  of 
nitrate  of  potassa  ; ignite  cautiously,  dissolve  the  residue  in  hydrochlo- 
ric acid,  evaporate  to  dryness  on  the  water-bath,  treat  with  hydrochlo- 
ric acid  and  water,  filter,  add  ammonia  to  the  filtrate  to  alkaline  reac- 
tion, then  acetic  acid  until  the  phosphate  of  lime  is  redissolved,  and 
lastly — without  previously  filtering  off  the  very  trifling  precipitate  of 
phosphate  of  sesquioxide  of  iron — acetate  of  sesquioxide  of  uranium,  and 
determine  the  phosphoric  acid  as  directed  p.  272,  c. 

d.  Determination  of  Nitrogen , after  § 185. — As  mixing  the  guano  in 
the  mortar  with  soda-lime  would  be  attended  with  escape  of  an  appre- 
ciable amount  of  ammonia,  it  is  advisable  to  effect  this  operation  in  the 
combustion  tube,  with  the  aid  of  a wire  (comp.  pp.  426 — 8). 

CL  Analysis  of  Bone  Dust 
§ 234. 

There  are  three  sorts  of  bone  dust. 

I.  The  powder  obtained  by  the  grinding  of  more  or  less  fresh  bones, 
which  is  generally  very  coarse.* 

II.  The  powder  obtained  by  the  grinding  of  more  or  less  decayed 
bones. 

III.  The  powder  of  bones  which,  previous  to  the  operation  of  grind- 
ing, have  been  submitted  to  the  action  of  boiling  water,  or  high-pressure 
steam. 

I.  is  very  coarse,  and  contains  a relatively  large  proportion  of  fat  and 
of  gelatigenous  matter.  II.  is  considerably  poorer  in  organic  substances. 
III.  is  much  finer  than  I.  and  II.  ; it  contains  hardly  any  fat,  and  is 
somewhat  poorer  in  gelatigenous  matter. 

1.  Examine  the  powder,  in  the  first  place,  by  careful  inspection, 
sifting,  and  elutriation,  to  ascertain  the  degree  of  comminution,  and  the 
presence  of  foreign  matters. 

2.  Determination  of  the  Water. — Dry  a sample  at  125°. 

3.  Total  amount  of  fixed  Constituents. — Ignite,  about  5 grm.,  with 
access  of  air,  until  the  ash  appears  white;  moisten  with  carbonate  of 
ammonia,  dry,  ignite  gently,  and  weigh  the  residue. 

4.  Fixed  Constituents  singly. — Treat  the  ash  of  3 with  dilute  hydro- 
chloric acid,  filter  off  the  insoluble  portion  (sand,  &c.),  and  determine 
the  sesquioxide  of  iron,  lime,  magnesia,  chloride  of  sodium,  and  phos- 
phoric acid  in  the  solution  as  directed  § 232,  4. 

5.  Nitrogen. — Ignite  0*5 — 0*8  grm.  with  soda-lime  (§185). 

6.  Fat. — Exhaust  5 grm.  of  the  sample  (ground  as  finely  as  possible), 
by  boiling  with  ether,  and  dry  the  residue  at  125°.  The  loss  of  weight 
minus  the  moisture  found  in  2,  shows  the  amount  of  fat.  By  way  of 


* [“  Flour  of  bone  ” obtained  from  fresh  bones  contains  several  per  cent,  of 
common  salt  to  preserve  it  from  putrefaction.] 


548 


SPECIAL  PART. 


control,  the  ether  may  be  distilled  off,  and  the  residual  fat  weighed,  care 
being  taken  to  leave  no  water  under  the  fat. 

7.  Deduct  from  the  total  weight  the  sum  of  the  fixed  constituents, 
carbonic  acid,  water,  and  fat ; the  difference  expresses  the  gelatigenous 
matter. 

8.  Determine  the  carbonic  acid  after  p.  293  e. 


D.  Analysis  of  Superphosphate. 

§ 235. 

Substances  which  contain  basic  phosphate  of  lime  in  a difficultly  solu- 
ble condition,  are  often  converted  into  so-called  superphosphate , for  the 
purpose  of  rendering  the  phosphoric  acid  soluble,  and  consequently  more 
readily  accessible  to  plants.  This  is  done  by  subjecting  them  to  the 
action  of  a certain  quantity  of  acid,  usually  sulphuric  (occasionally  as- 
sociated with  hydrochloric),  by  which  sulphate  of  lime  (and  chloride  of 
calcium),  acid  phosphate  of  lime  and  phosphoric  acid  are  formed.* 

The  following  bodies  are  employed  for  the  preparation  of  superphos- 
phate, viz.,  spent  bone-black  from  sugar  refineries,  coprolite,  apatite, 
phosphorite,  Baker  guano,  precipitated  basic  phosphate  of  lime  from 
glue  works,  and,  more  rarely,  bone  dust. 

As  it  is  unusual  to  employ  enough  acid  to  set  the  whole  of  the  phos- 
phoric acid  free,  the  superphosphates  generally  consist  of  mixtures  of 
sulphate  of  lime  (and  chloride  of  calcium),  basic  phosphate  of  lime,  phos- 
phate of  sesquioxide  of  iron,  phosphoric  acid,  and  water.  Carbon  or 
organic  matter  (containing  nitrogen)  is  frequently  also  present.  Their 
quality  is  very  variable,  according  to  the  raw  material  employed  and  the 
method  of  treatment,  but  they  all  agree  in  this,  that  they  consist  of  sub- 
stances (a)  readily  soluble  in  water,  (6)  difficultly  soluble  in  water,  and 
(c)  insoluble  in  water. 

Before  we  can  judge  of  the  value  of  a superphosphate  it  is  abso- 
lutely necessary  to  know,  not  merely  the  quantity  of  the  constituents, 
but  how  they  are  combined  and  how  they  deport  themselves  with  sol- 
vents ; hence  the  analysis  becomes  somewhat  complicated. 

1.  Dry  about  3 grm.  of  the  sample  at  160 — 180°.  The  loss  of  weight 
expresses  a,  the  moisture  y b,  the  water  of  the  sulphate  of  lime. 

2.  Triturate  10  grm.  of  the  undried  superphosphate  in  a dish  with 
cold  water  by  the  aid  of  a pestle,  till  all  the  lumps  are  completely  bro- 
ken down,  allow  to  settle,  pour  off  the  clear  supernatant  fluid  through  a 
filter,  and  repeat  the  extraction  with  cold  water,  till  the  fluid  no  longer 
shows  acid  reaction.  Dilute  the  aqueous  solution  so  obtained  to  500 
c.  c.,  and  dry  the  residue  at  about  100°. 

3.  Divide  the  aqueous  solution , which  generally  appears  yellow  from 
the  presence  of  organic  matter,  into  4 portions,  viz.,  a,  b}  and  c,  of  100 
c.  c.  each,  and  d,  of  200  c.  c. 

a.  Evaporate  in  a platinum  dish,  adding,  after  some  time,  cautiously, 
thin  milk  of  lime  just  to  distinct  alkaline  reaction;  proceed  with  the 
evaporation,  dry  the  residue  at  180°,  and  weigh;  ignite  the  weighed 


* Comp.  Reinh.  Weber;  Pogg.  Annal.  109,  505. 


ANALYSIS  OF  SUPERPHOSPHATE. 


549 


§ 235.] 

residue  and  weigh  again : the  difference  between  the  two  weighings  ex- 
presses the  quantity  of  organic  matter  in  the  aqueous  solution.  Boil 
the  residue  with  pure  lime-water,  then  with  water,  filter,  precipitate  the 
sulphuric  acid  from  the  filtrate  by  addition  of  a little  chloride  of  barium, 
then  the  baryta  and  lime  by  carbonate  of  ammonia,  and  determine  the 
alkalies  as  chlorides  according  to  p.  345,.  15- 

b.  Precipitate  with  chloride  of  barium,  and  determine  the  sulphuric 
acid  in  the  usual  way  (§  132,  I.,  1). 

c.  Serves  for  the  determination  of  any  hydrochloric  acid  after  § 141. 
Organic  matter,  if  present  in  large  quantity,  is  destroyed  as  in  d. 

d.  Add  an  excess  of  carbonate  of  soda  and  a little  nitrate  of  potassa, 
and  evaporate  to  dryness  in  a platinum  dish.  Ignite  the  residue  gently, 
then  soften  with  water,  rinse  into  a beaker,  add  hydrochloric  acid,  and 
apply  a gentle  heat  until  complete  solution  is  effected.  Add  to  the 
clear  fluid,  ammonia,  then  acetic  acid  in  excess  ; filter  off  the  phosphate 
of  sesquioxide  of  iron , and  divide  the  filtrate  into  two  equal  portions. 
Determine  in  one  the  phosphoric  acid  * with  uranium  solution  either 
gravimetrically,  after  p.  272,  c,  or  by  the  volumetric  method,  p.  274. 
Estimate  in  the  other  portion  the  lime  and  magnesia  as  directed  p. 

349,  29. 

4.  Transfer  the  residue  of  2 to  a weighed  platinum  dish,  add  the  ash 
of  the  filter,  dry  at  180°,  and  weigh.  The  weight  expresses  the  total 
amount  of  substances  insoluble  in  water.  Now  ignite  gently,  with  access 
of  air,  until  the  whole  of  the  organic  matter  and  charcoal  is  burnt ; the 
loss  of  weight  indicates  the  amount  of  these  latter. 

5.  Boil  the  residue  of  4 with  dilute  hydrochloric  acid  ; after  boiling 
for  some  time,  dilute  with  water,  filter,  and  dilute  the  filtrate  by  means 
of  the  washing  water  to  \ litre  ; treat  the  insoluble  residue  as  directed 
in  7. 

6.  Of  the  hydrochloric  acid  solution  obtained  in  5,  measure  off  two 
portions,  one  of  50,  the  other  of  100  c.  c.  In  the  former  determine  the 
sulphuric  acid , in  the  latter  the  phosphate  of  sesquioxide  of  iron  (if 
present),  lime , magnesia , and  phosphoric  acid*  as  in  3,  b and  d. 

7.  Dry,  ignite,  and  weigh  the  insoluble  residue  of  5.  It  generally 
consists  only  of  sand , clay , and  silicic  acid.  To  make  quite  sure,  how- 
ever, boil  with  concentrated  hydrochloric  acid  ; should  some  more  sul- 
phate of  lime  be  dissolved,  determine  the  amount  of  this  in  the  solu- 
tion. 

8.  Lastly,  determine  the  nitrogen  in  0*8 — 1 grm.  of  the  superphos- 
phate (§  185).  In  arranging  the  results,  it  must  not  be  forgotten  that 
the  nitrogen  is  part  of  the  organic  matter  previously  determined. 

9.  Should  the  superphosphate  contain  an  ammonia  salt,  determine 
the  ammonia  as  directed  p.  157,  3,  a. 

As  regards  the  statement  of  the  results,  the  following  plan  presents  a 
very  good  bird’s-eye  view  of  the  analysis  : — 


* [ Many  superphosphates  contain  considerable  quantities  of  phosphates  of  iron 
and  alumina  which  are  to  some  extent  extracted  by  water.  In  such  cases  the 
above  method  will  not  give  good  results,  but  both  the  soluble  and  insoluble 
phosphoric  acid  must  be  separated  by  means  of  molybdic  solution,  either  from  the 
original  solution  in  water  or  hydrochloric  acid,  or  from  the  acetate  of  ammonia 
precipitate.  See  p.  271.] 


550 


SPECIAL  PART. 


[§  236 


f Hydrate  of  phosphoric  acid  (3  H 0,  P05). 


Constituents  \ Lime, 
readily  solu-  { Magnesia, 
ble  in  water.  Sesquiox.  iron, 
[Potash, 


dissolved  by,  or  com- 
bined with,  the  free 
phosphoric  acid 


16  15 
0-50 


Anhydrous 
phosphoric  Nitro- 
acid.  gen. 

11-70  — 


Constituents ) 

[■  Sulphate  of  lime  (CaO,  S03-f  2 aq.) 42  00 


soluble  in 
water. 

Constituent; 


J 


soluble  in  -i  ™me’  . 


f Phosphoric  acid 2*19  2’19  — 


acids. 


f Magnesia, 

{ Sesquiox.  iron,  ) 


combined  with  the 
]■  phosphoric  acid  to  more 
or  less  basic  salts 

Constituents  ) 

insoluble  in  >•  Clay  and  sand 2 49 

acids.  ) 

Organic  constituents  and  carbon 6 51 

Moisture 29-15 


101  — — 


0-41 

0-41 


100  00  13  89 


It  will  be  seen  that  we  calculate  the  sulphuric  acid  found  in  solution 
and  residue  into  sulphate  of  lime,  and  add  both  the  quantities  together. 
The  residual  quantities  of  lime  in  the  solution  and  the  residue,  i.e.y  the 
portions  not  combined  with  sulphuric  acid,  are  then  put  down  as  above. 
If  the  superphosphate  was  prepared  with  sulphuric  and  hydrochloric 
acids,  the  chlorine  in  the  aqueous  solution  is  to  be  calculated  into  chlo- 
ride of  calcium,  and  the  lime  corresponding  thereto  + the  lime  combined 
with  sulphuric  acid  is  to  be  deducted  from  the  total  quantity  found  in 
the  aqueous  solution.  The  remainder  is  then  to  be  put  down  as  dis- 
solved by,  or  combined  with,  phosphoric  acid. 


[Abridged  Analysis  of  Superphosphates. 

§ 236. 

For  most  ordinary  purposes  it  is  sufficient  to  estimate  on  1 grin. — 

A.  I Vetter  expelled  at  100°  by  drying  in  water-bath. 

B.  Organic  and  other  volatile  matters  by  gentle  ignition  and  incine- 
ration of  A until  carbon  is  mostly  consumed. 

C.  Sand  and  insoluble  matters  by  treatment  of  the  residue  of  B with 
nitric  acid. 

D.  Total  phosphoric  acid  in  ^ of  the  solution  C by  means  of  molyb- 
dic  solution,  when  iron  and  alumina  are  present  in  quantities  of  over 

per  cent. ; or,  in  absence  of  iron  and  alumina,  by  titration  with  stand- 
ard uranium  solution. 

E.  Soluble  phosphoric  acid  by  treating  10  grm.  as  directed  above, 
§ 235,  2 and  estimating  phosphoric  acid  in  aliquot  parts  (50  c.  c.)  of  the 
solution,  with  uranium  or  molybdic  solution — see  foot-note  p.  549. 

F.  Nitrogen  in  0*5  grm.  by  combustion  with  soda  lime,  § 185. 

More  important  than  determining  the  quantities  of  lime,  magnesia, 

&c.,  is  a study  of  the  condition  of  the  phosphates  insoluble  in  water,  and 
of  the  nitrogen.  The  former  are  much  more  valuable  as  fertilizers 
when  existing  as  bone-earth  than  when  composed  of  crystallized  apatite 


237,  238.] 


ANALYSIS  OF  BONE  BLACK. 


551 


or  compact  coprolite.  The  latter  in  gelatine  or  blood  is  very  active, 
while  in  the  form  of  leather  shavings  it  is  nearly  inert.] 

E.  Analysis  of  Bone  Black. 


§ 237. 

Bone  black  is  extensively  employed  for  decolorizing  and  removing  the 
lime  from  the  juice  in  the  preparation  of  beetroot  sugar,  and  in  the  re- 
fining of  cane  sugar.  When  freshly  prepared  it  consists  of  a mixture  of 
bone  earth  with  7 — 10  per  cent,  of  carbon,  but  on  use  it  takes  up  lime, 
coloring  matter,  mucilage,  &c.,  from  which  it  is  freed  during  the  process 
of  reanimation,  by  washing,  treating  with  hydrochloric  acid,  washing 
again,  drying  and  igniting.  When  at  last  it  is  thoroughly  used  up,  or 
“ spent,”  it  passes  into  the  manure  manufactories,  and  is  then  generally 
applied  to  the  preparation  of  superphosphate.  As  the  bone  black  is 
much  altered  and  contaminated  by  the  numerous  operations  through 
which  it  passes,  its  value  varies  very  considerably,  and  can  only  be  es- 
timated by  analysis.  Again,  before  being  submitted  to  the  revivifying 
process,  bone  black  always  requires  testing,  in  order  that  it  may  be 
known  how  much  hydrochloric  acid  it  is  necessary  to  employ ; in  this 
case  we  have  to  find  the  quantity  of  the  lime  which  is  not  combined 
with  phosphoric  acid  (and  which  is  usually  present  in  the  form  of  carbo- 
nate of  lime). 

We  describe,  in  the  first  place,  the  ordinary  method  of  analyzing 
bone  black,  and  then  a process  for  determining  the  carbonate  of  lime. 

General  Process. 

1.  Dry  2 — 3 grm.  at  160 — 180.°.  The  loss  of  weight  indicates  the 
moisture. 

2.  Dissolve  5 grm.  in  the  flask  a of  the  apparatus  figured  p.  293,  and 
determine  the  carbonic  acid  as  there  described. 

3 Filter  the  solution  through  a weighed  filter,  wash  the  residue, 
dry  at  100°,  and  weigh.  This  will  give  you  the  sum  of  the  charcoal, 
the  insoluble  organic  matter  and  the  mineral  impurities  insoluble 
in  hydrochloric  acid  (sand  and  clay).  Now  ignite  the  dried  filter 
with  access  of  air.  This  will  give  you  the  sand  and  clay  as  the  resi- 
due. The  charcoal  and  insoluble  organic  matter  is  found  by  difference. 

4.  Make  the  filtrate  obtained  in  3 up  to  250  c.  c.  and  determine  in 
100  c.  c.  iron,  lime , magnesia , and  phosphoric  acid , in  50  c.  c.  the  sul- 
phuric acid,  that  may  be  present,  and  in  the  last  100  c.  c.  the  alkalies 
possibly  present  according  to  § 232,  b.  p.  544. 

5.  Dissolve  another  weighed  portion  of  the  substance  in  dilute  nitric 
acid,  dilute  and  determine  in  the  filtrate  the  hydrochloric  acid  possibly 
present. 

Process  for  Determining  the  Carbonate  of  Lime  or  the  Car- 
bonate of  Lime  and  Caustic  Lime. 

§ 238. 

* For  determining  carbonate  of  lime  3 grm.  of  the  bone  black  are  dried 
and  powdered  as  finely  as  possible.  Estimate  carbonic  acid  according  to 


552 


SPECIAL  PART. 


g , p.  298,  from  this  calculate  the  carbonate  of  lime.  If  a bone  black 
contains  hydrate  of  lime,  moisten  a portion  weighed  off  in  a porcelain 
dish  with  10 — 20  drops  of  carbonate  of  ammonia,  evaporate  to  dryness, 
heat  the  residue  somewhat  more  strongly  (but  by  no  means  to  ignition), 
and  transfer  without  loss  to  the  decomposing  bottle.  Calculate  as  be- 
fore ; the  excess  over  the  first  estimation  is  carbonate  equivalent  to  the 
caustic  lime  present. 

§ 239. 

19.  [Analysis  of  Coal  and  Peat. 

For  technical  purposes,  estimations  of  moisture,  ash,  coke,  and  volatile 
matters  usually  suffice.  Determination  of  sulphur  is  less  frequently 
required,  and  ultimate  analysis  is  only  resorted  to  in  special  cases. 

a.  Moisture.  The  finely  pulverized  coal  (3 — 5 grm.)  is  heated  to 
110 — 115°  for  an  hour  or  more,  or  until  it  ceases  to  lose  weight  (see  § 29). 
Many  bituminous  coals  gain  weight  after  a time  from  oxidation  of  sul- 
phides or  hydro- carbons  (Whitney).  According  to  Hinrichs,*  drying 
the  coal  for  one  hour  effects  the  maximum  loss. 

b.  Coke  and  volatile  matters.  The  dried  coal  of  a is  sharply  heated 
in  a closed  platinum,  or,  in  presence  of  sulphides,  in  a porcelain  crucible 
as  long  as  combustible  matters  issue  from  it.  It  is  then  cooled  quickly. 
The  loss  is  set  down  as  volatile  matters.  The  residue,  less  the  ash,  is 
coke. 

c.  Ash.  The  residue  of  b is  incinerated  in  a crucible  placed  aslant. 

d.  Carbon  and  hydrogen  are  determined  by  combustion  with  chromate 
of  lead  and  bichromate  of  potash,  § 177. 

e.  Nitrogen  is  estimated  according  to  § 185. 

f.  Sulphur  is  determined  as  directed  § 219,  c.  p.  515,  but  the  evapora- 
tion with  hydrochloric  acid  is  omitted,  and  the  sulphate  of  baryta,  after 
decanting  the  supernatant  liquid  upon  a filter,  is  boiled  up  two  or  three 
times  with  dilute  solution  of  acetate  of  ammonia,  to  free  it  from  adhering 
salts.  Storer  and  Pearson.] 


* Chemical  News,  19,  282. 


III.  ANALYSIS  OF  ATMOSPHERIC  AIR. 


§ 240. 

In  the  analysis  of  atmospheric  air  we  usually  confine  our  attention  to  the 
following  constituents  : oxygen,  nitrogen,  carbonic  acid,  and  aqueous 
vapor.  It  is  only  in  exceptional  cases  that  the  exceedingly  minute  quan- 
tities of  ammonia  and  other  gases — many  of  which  may  be  assumed  to 
be  always  present  in  infinitesimal  traces — are  also  determined. 

It  does  not  come  within  the  scope  of  the  present  work  to  describe  all 
the  methods  which  have  been  employed  in  the  capital  investigations 
made  in  the  last  few  years  by  Brunner,  Bunsen,  Dumas  and  Boussin- 
gault,  Regnault  and  Reiset,  and  others.  To  these  methods  we  are 
indebted  for  a more  accurate  knowledge  of  the  composition  of  our  atmo- 
sphere, and  excellent  descriptions  of  them  will  be  found  in  the  works 
below.* 

I confine  myself  to  those  methods  which  are  found  most  convenient  in 
the  analysis  of  the  air  for  medical  or  technical  purposes. 

A.  Determination  of  the  Water  and  Carbonic  Acid. 

§ 241. 

It  was  formerly  the  custom  to  effect  these  determinations  by  Brunner’s 
method,  which  consisted  in  slowly  drawing,  by  means  of  an  aspirator,  a 
measured  volume  of  air  through  accurately  weighed  apparatuses  filled 
with  substances  having  the  property  of  retaining  the  aqueous  vapor  and 
the  carbonic  acid,  and  estimating  these  two  constituents  by  the  increased 
weights  of  the  apparatuses. 

Fig.  102  represents  the  arrangement  recommended  by  Regnault. 

The  vessel  V is  made  of  galvanized  iron,  or  of  sheet  zinc  ; it  holds 
from  50  to  100  litres,  and  stands  upon  a strong  tripod  in  a trough  large 
enough  to  hold  the  whole  of  the  water  that  V contains.  At  a a brass 
tube  c,  with  stopcock,  is  firmly  fixed  in  with  cement.  Into  the  aperture 
5,  which  serves  also  to  fill  the  apparatus,  a thermometer  reaching  down 
to  the  middle  of  V is  fixed  air-tight  by  means  of  a perforated  cork 
soaked  in  wax. 

The  efflux  tube,  r,  which  is  provided  with  a cock,  is  bent  slightly  up- 
ward, to  guard  against  the  least  chance  of  air  entering  the  vessel  from 
below.  The  capacity  of  the  vessel  is  ascertained  by  filling  it  completely 
with  water,  and  then  accurately  measuring  the  contents  in  graduated 
vessels.  The  end  of  the  tube  c is  connected  air-tight  with  A7,  by  means 
of  a caoutchouc  tube ; the  tubes  A — F are  similarly  connected  with  one 
another.  A,  F,  F,  and  F are  filled  with  small  pieces  of  glass  moistened 

* Ausfiihrliches  Handbuch  der  analytischen  Ohemie  von  H.  Rose,  II.  853 ; 
Graham -Otto’s  ausfiihrliches  Lehrbuch  der  Chemie,  Bd.  II.  Abth.  1,  S.  102  etseq.; 
Handworterbuch  der  Chemie  von  Liebig,  Poggendorff  und  Wohler,  2 Aufl.  Bd.  II. 
S.  431  et  seq.  ; and  Bunsen’s  Gasometry. 


554 


SPECIAL  PART. 


L§  241. 


with  pure  concentrated  sulphuric  acid,  C and  D with  moist  hydrate  of 
lime.*  Finally,  A is  also  connected  with  a long  tube  leading  to  the 


Fig.  102. 


place  from  which  the  air  intended  for  analysis  is  to  be  taken.  The  corks 
of  the  tubes  are  coated  over  with  sealing-wax.  The  tubes  A and  1 3 are 
intended  to  withdraw  the  moisture  from  the  air ; they  are  weighed  to- 
gether. C,  D , and  E are  also  weighed  jointly.  C and  E absorb  the 
carbonic  acid ; E the  aqueous  vapor  which  may  have  been  withdrawn 
from  the  hydrate  of  lime  by  the  dry  air.  F need  not  be  weighed  ; it 
simply  serves  to  protect  E against  the  entrance  of  aqueous  vapor  from  T7! 

The  aspirator  is  completely  filled  with  water ; c is  then  connected  with 
E,  and  thus  with  the  entire  system  of  tubes ; the  cock  r is  opened  a 
little,  just  sufficiently  to  cause  a slow  efflux  of  water.  As  the  height  of 
the  column  of  water  in  V is  continually  diminishing,  the  cock  must  from 
time  to  time  be  opened  a little  wider,  to  maintain  as  nearly  as  possible  a 
uniform  flow  of  water.  When  V is  completely  emptied,  the  height  of 
the  thermometer  and  that  of  the  barometer  are  noted,  and  the  tubes  A 
and  E , and  (7,  E,  and  E weighed  again. 

As  the  increase  of  weight  of  A and  E gives  the  amount  of  water,  that 
of  C , E,  and  E ’,  the  amount  of  carbonic  acid,  in  the  air  which  has 
passed  through  them ; and  as  the  volume  of  the  latter  (freed  from  water 
and  carbonic  acid)  is  accurately  known  from  the  ascertained  capacity 

* With  regard  to  C and  D , I have  returned  to  lime,  preferring  it  to  pumice 
saturated  with  solution  of  potash,  because,  as  Hlasiwetz  (them.  Centralbl.  1856, 
575)  has  shown,  the  solution  of  potash  absorbs  not  only  carbonic  acid,  but  also 
oxygen.  Indeed,  H.  Rose  had  previously  made  a similar  observation.  With  re- 
spect to  the  other  tubes,  I prefer  the  concentrated  sulphuric  acid  to  chloride  of 
calcium  as  the  absorbent  for  water  (see  Pettenkofer,  Sitzungsber.  der  bayer. 
Akad.  1862,  II.  Heft  1,  S.  59).  Hlasiwetz’s  statement,  that  concentrated  sulphuric 
acid  also  takes  up  carbonic  acid,  I have  found  to  be  unwarranted.  Chloride  of 
calcium  does  not  dry  the  air  completely,  and,  besides.  Hlasiwetz  says  that  when 
it  is  used  a trace  of  chlorine  is  carried  away  corresponding  to  the  amount  of  ozone 
in  the  air  (op.  cit.  p.  517). 


ANALYSIS  OF  ATMOSPHERIC  AIR. 


555 


§ 241.] 

of  V:  * the  calculation  is  in  itself  very  simple ; but  it  involves,  at 
least  in  very  accurate  analyses,  the  following  corrections  : — 

a.  Reduction  of  the  air  in  V,  which  is  saturated  with  aqueous  vapor, 
to  dry  air  ; since  the  air  which  penetrates  through  c is  dry  (see  § 195,  y). 

/?.  Reduction  of  the  volume  of  dry  air  so  found  to  0°,  and  760  mm. 
(§  195,  « and  /?). 

When  these  calculations  have  been  made,  the  weight  of  the  air  which 
has  penetrated  into  V is  readily  found  from  the  datum  in  Table  V.  at 
the  end  of  the  volume  ; and  as  the  carbonic  acid  and  water  have  also 
been  weighed,  the  respective  quantities  of  these  constituents  of  the  air 
may  now  be  expressed  in  per-cents  by  weight,  or,  calculating  the  weights 
into  volumes,  in  per-cents  by  measure. 

Considering  the  great  weight  and  size  of  the  absorption  apparatus,  in 
comparison  to  the  increase  of  weight  by  the  process,  at  least  25,000  c.  c. 
of  air  must  be  passed  through  ; the  air  inside  the  balance-case  must  be 
kept  as  dry  as  possible  by  means  of  a sufficient  quantity  of  chloride  of 
calcium,  and  the  apparatus  left  for  some  time  in  the  balance-case,  before 
proceeding  to  weigh.  Neglect  of  these  measures  would  lead  to  considera- 
ble errors,  more  particularly  as  regards  the  carbonic  acid,  the  quantity 
of  which  in  atmospheric  air  is,  on  an  average,  about  10  times  less  than 
that  of  the  aqueous  vapor  (comp.  Hlasiwetz,  loc.  cit.). 

For  the  exact  determination  of  the  carbonic  acid  one  of  the  following 
methods  is  far  better  suited  : — 

a.  Process  suggested  by  Fr.  Mohr,  applied,  and  carefully  tested  by  H. 
v.  GiLM.f  Von  Gtlm  employed  in  his  experiments  an  aspirator  holding 
at  least  30  litres,  which  was  arranged  like  that  shown  in  fig.  102,  but 
had  a third  aperture,  bearing  a small  manometer.  The  air  was  drawn 
through  a tube,  1 metre  long,  and  about  1 5 mm.  wide  ; this  tube  was 
drawn  out  thin  at  the  upper  end,  and  at  the  lower  end  bent  at  an  angle 
of  140 — 150°.  It  was  more  than  half  filled  with  coarse  fragments  of 
glass  and  perfectly  clear  baryta  water,  and  fixed  in  such  a position  that 
the  long  part  of  it  was  inclined  at  an  angle  of  8 — 10°  to  the  horizontal. 
A narrow  glass  tube,  fitted  into  the  undrawn-out  end  of  the  tube  by 
means  of  a cork,  served  to  admit  the  air.  Two  small  flasks,  filled  with 
baryta  water,  were  placed  between  the  absorption  tube  and  the  aspira- 
tor ; these* were  intended  as  a control,  to  show  that  the  whole  of  the 
carbonic  acid  had  been  retained.  When  about  60  litres  of  air  had  slowly 
passed  through  the  absorption  tube,  the  carbonate  of  baryta  formed  was 
filtered  off  out  of  contact  of  air,  and  the  tube  as  well  as  the  contents  of 
the  filter  washed,  first  with  distilled  water  saturated  with  carbonate  of 
baryta,  then  with  pure  boiled  water.  The  carbonate  of  baryta  in  the 
filter  and  in  the  tube  was  then  dissolved  in  dilute  hydrochloric  acid,  the 
solution  evaporated  to  dryness,  the  residue  gently  ignited,  and  the  chlo- 
rine of  the  chloride  of  barium  determined  as  directed  § 141,  b,  a.  1 eq. 
chlorine  represents  1 eq.  carbonic  acid.  It  is  obvious  that  one  may  also 
determine  the  baryta  in  the  hydrochloric  acid  solution  by  precipitating 
with  sulphuric  acid.  For  filtering  the  carbonate  of  baryta,  v.  Gilm  em- 
ployed a double  funnel  (fig.  103) ; the  inner  cork  has,  besides  the  per- 


* Or  from  the  quantity  of  water  which  has  flown  from  V,  as  the  experiment 
may  be  altered  in  this  way,  that  a portion  only  of  the  water  is  allowed  to  run 
out,  and  received  in  a measuring  vessel, 
f Chem.  Centralbl.  1857,  760. 


556 


SPECIAL  PART. 


foration  through  which  the  neck  of  the  funnel  passes,  a lateral  slit,  which 
establishes  a communication  between  the  air  in  the  outer  funnel  and  the 

As,  with  the  absorption  apparatus  arranged  as  de- 
scribed, the  air  has  to  force  its  way  through  a column 
of  fluid,  the  manometer  is  required  to  determine  the 
actual  volume  of  the  air  ; the  height  indicated  by  this 
instrument  being  deducted  from  the  barometric  pres- 
sure observed  during  the  process. 

Fr.  Mohr*  now  recommends  as  the  absorbent 
fluid  a solution  of  baryta  in  potash.  This  is  prepared 
by  dissolving  crystals  of  baryta  in  weak  solution  of 
potash  with  the  aid  of  heat,  and  filtering  off  the  car- 
bonate of  baryta,  which  invariably  forms  in  small 
quantity.  The  dear  filtrate  is  accordingly  saturated 
with  carbonate  of  baryta.  Mohr  now  leaves  out  the 
fragments  of  glass. 

This  method  afforded  v.  Gilm  very  harmonious 
results.  Nevertheless,  it  involves  one  source  of  error.  If  clear  baryta 
water  is  passed  through  paper  with  the  most  careful  possible  exclusion 
of  air,  and  the  filter  is  washed  till  the  washings  are  free  from  baryta, 
and  dilute  hydrochloric  acid  is  then  poured  upon  the  filter,  and  the 
filtrate  thus  obtained  is  evaporated,  a small  quantity  of  chloride  of  barium 
will  be  left,  showing  that  a little  baryta  was  kept  back  by  the  paper. 
Al.  Muller  f has  already  called  attention  to  the  capacity  of  filter  paper 
for  retaining  baryta. 

b.  M.  Pettenkofer’s  process. \ 

a.  Principle  and  Requisites. — A known  volume  of  air  is  made  to  act 
upon  a definite  quantity  of  standard  baryta  water  (standardized  by 
oxalic  acid  solution),  in  such  manner  that  the  carbonic  acid  is  completely 
bound  by  the  baryta.  The  baryta  water  is  then  poured  out  into  a 
cylinder,  and  allowed  to  deposit  with  exclusion  of  air,  a part  of  the  clear 
fluid  is  then  removed,  and  the  baryta  remaining  in  solution  is  determin- 
ed. The  difference  between  the  oxalic  acid  required  for  a certain  quan- 
tity of  baryta  water  before  and  after  the  action  of  the  air,  represents  the 
carbonate  of  baryta  formed,  and  consequently  the  carbonic  acid  present. 

Two  kinds  of  baryta  water  are  used  : one  contains  21  grm.  and  the 
other  7 grm.  crystallized  hydrate  of  baryta  ||  in  the  litre ; these  serve 
for  the  determination  of  larger  and  smaller  quantities  of  carbonic  acid 


* Lehrbuch  der  Titrirmethode,  2d  ed.  446. 

f Joum.  f.  prakt.  Chem.  83,  384. 

$ Abhandl.  der  naturw.  u.  tecbn.  Commission  der  k.  bayer.  Akad.  der  Wiss.  II 
1 ; Ann.  d.  Chem.  u.  Pharm.  II.  Supplem.  Bd.  p.  1. 

| The  hydrate  of  baryta  must  be  entirely  free  from  caustic  potash,  and  soda, 
the  smallest  quantities  of  which  render  the  volumetric  estimation  in  the  presence 
of  carbonate  of  baryta  impossible,  since  the  neutral  alkaline  oxalates  decompose 
the  alkaline  earthy  carbonates.  When  a trace  even  of  carbonate  of  baryta  is 
suspended  in  the  fluid — and  this  is  always  the  case  when  a baryta  water  which 
has  been  used  for  the  absorption  of  carbonic  acid  is  not  filtered — the  reaction 
continues  alkaline  if  the  smallest  trace  of  potash  or  soda  is  present,  because  the 
alkaline  oxalate  formed  immediately  enters  into  decomposition  with  the  carbon- 
ate of  baryta.  A fresh  addition  of  oxalic  acid  converts  the  alkaline  carbonate 
again  into  oxalate,  and  the  fluid  is  for  a moment  neutral,  till,  on  shaking  with 


air  in  the  bottle. 


§ 241.] 


ANALYSIS  OF  ATMOSPHERIC  AIR. 


557 


respectively.  1 c.  c.  of  the  stronger  corresponds  to  about  3 mgrm.  car 
bonic  acid,  of  the  weaker  1 c.  c.  corresponds  to  about  1 mgrm.* * 

The  oxalic  acid  solution  which  serves  for  standardizing  the  baryta 
water  contains  2*8636  grm.  cryst.  oxalic  acid  in  1 litre.  1 c.  c.  corre- 
sponds to  1 mgrm.  carbonic  acid.  The  baryta  water  is  standardized  as 
follows : — transfer  30  c.  c.  of  it  to  a flask,  and  then  run  in  the  oxalic  acid 
from  a Mohr’s  burette  with  float ; shake  the  fluid  from  time  to  time, 
closing  the  mouth  of  the  flask  with  the  thumb.  The  vanishing  point  of 
the  alkaline  reaction  is  ascertained  with  delicate  turmeric  paper,  f As 
soon  as  a drop  of  the  fluid  placed  on  the  paper  does  not  give  a brown 
ring,  the  end  is  attained.  If  you  were  obliged,  in  the  first  experiment, 
to  take  out  too  many  drops  for  testing  with  turmeric  paper,  consider  the 
result  as  only  approximate,  and  make  a second  experiment,  adding  at 
once  the  whole  quantity  of  oxalic  acid  to  within  1 or  \ c.  c.  and  then 
beginning  to  test  with  paper.  A third  experiment  would  be  found  to 
agree  with  the  second  to  yL  c.  c.  The  reaction  is  so  sensitive  that  all 
foreign  alkaline  matter,  particles  of  ash,  tobacco  smoke,  &c.,  must  be  care- 
fully guarded  against. 

(3.  The  actual  Analysis. — This  may  be  effected  in  two  different  ways. 

aa.  Take  a perfectly  dry  bottle,  of  about  6 litres  capacity,  with  well- 
fitting ground  glass  stopper,  and  accurately  determine  the  capacity ; fill 
the  bottle,  by  means  of  a pair  of  bellows,  with  the  air  to  be  analyzed  ; 
add  45  c.  c.  of  the  dilute  standard  baryta  water,  and  cause  the  baryta 
water  to  spread  over  the  inner  surface  of  the  bottle,  by  turning  the  latter 
about,  but  without  much  shaking.  In  the  course  of  about  \ an  hour  the 
whole  of  the  carbonic  acid  is  absorbed.  Pour  the  turbid  baryta  water 
into  a cylinder,  close  securely,  and  allow  to  deposit ; then  take  out,  by 
means  of  a pipette,  30  c.  c.  of  the  clear  supernatant  fluid,  run  in  standard 
oxalic  acid,  multiply  the  volume  used  by  1*5  (as  only  30  c.  c.  of  the 
original  45  are  employed  in  this  experiment),  and  deduct  the  product 
from  the  c.  c.  of  oxalic  acid  used  for  45  c.  c.  of  the  fresh  baryta  water ; 
the  difference  represents  the  quantity  of  baryta  converted  into  carbonate, 
and  consequently  the  amount  of  the  carbonic  acid.  If  the  air  is  unusually 
i*ich  in  carbonic  acid,  the  concentrated  baryta  water  is  employed. 

bb.  Pass  the  air  through  a tube  or  through  two  tubes  containing 
measured,  quantities  of  standard  baryta  water  and  finish  the  experiment 
as  in  aa.  For  passing  a definite  quantity  of  air  we  should  generally  employ 
an  aspirator  (p.  554) ; Pettenkofer  in  his  experiments  with  the  respi- 
ration apparatus  forced  the  air  by  means  of  small  mercurial  pumps  first 


air,  the  carbonic  acid  escapes,  and  any  carbonate  of  baryta  still  present  converts 
the  alkaline  oxalate  again  into  carbonate.  To  test  a baryta  water  for  caustic 
alkali,  determine  the  alkalinity  of  a perfectly  clear  portion,  and  then  of  a portion 
that  has  been  mixed  with  a little  pure  precipitated  carbonate  of  baryta.  If  you 
use  more  oxalic  acid  in  the  second  than  in  the  first  experiment,  caustic  alkali  is 
present,  and  some  chloride  of  barium  must  be  added  to  the  baryta  water  before 
it  can  be  used. 

* [The  baryta  water  is  kept  in  a bottle  under  a thin  stratum  of  kerosene 
(Mohr).  It  is  drawn  off  through  a syphon  supported  in  the  stopper,  the  outer 
leg  of  which  is  recurved  upwards  and  closed  with  a bit  of  rubber  tube  and  clip. 
By  having  this  leg  of  the  syphon  sufficiently  long  the  burette  may  be  filled  by 
inserting  its  delivery  end  in  the  rubber  tube  and  opening  both  clips.  ] 

f Prepared  with  lime-free  Swedish  filter  paper,  and  tincture  of  turmeric.  The 
spirit  used  in  making  the  latter  must  be  free  from  acid.  Dry  the  paper  in  a dark 
room,  and  keep  it  protected  from  the  light.  It  is  lemon  yellow. 


558 


SPECIAL  PART. 


through,  the  tubes,  and  then  through  an  apparatus  for  measuring  the  gas. 
The  form  and  arrangement  of  the  tubes  is  illustrated  by  fig.  104.  Two 
such  tubes  were  used ; the  first  was  1 metre,  the  second  *3  metres  long ; 
they  were  filled  with  baryta  water — the  former  with  the  stronger  solution, 
the  latter  with  the  weaker.  The  air  is  introduced  through  the  short 
limbs  of  the  tubes,  and  is  carried  beyond  the  bends  by  a narrow  flexible 
tube,  and  the  glass  tubes  themselves  are  so  inclined  that  the  bubbles  of 
air  move  on  with  the  necessary  rapidity  without  uniting.  The  motion 
of  the  gas  bubbles  keeps  up  a constant  mixing  of  the  baryta  water. 


B.  Determination  of  the  Oxygen  and  Nitrogen. 

§ 242. 

The  method  I shall  give  is  that  proposed  by  v.  Liebig.*  It  is  based 
nipon  the  observation  made  by  Chevreul  and  Dobereiner,  that  pyro- 
gallic  acid,  in  alkaline  solutions,  has  a powerful  tendency  to  absorb  oxygen. 


* Annal.  d.  Chern.  u.  Pharm.  77,  107. 


ANALYSIS  OF  ATMOSPHERIC  AIR. 


559 


§ 242.] 


1.  A strong  measuring  tube,  holding  30  c.  c.,  and  divided  into  ^ or 

c.  c.,  is  filled  to  -§-  with  the  air  intended  for  analysis.  The  remaining  part 
of  the  tube  is  filled  with  mercury,  and  the  tube  is  inverted  over  that 
fluid  in  a tall- cylinder,  widened  at  the  top. 

2.  The  volume  of  air  confined  is  measured  (§12).  If  it  is  intended 
to  determine  the  carbonic  acid  —which  can  be  done  with  sufficient  accu- 
racy only  if  the  quantity  of  the  acid  amounts  to  several  per-cents — the 
air  is  dried  by  the  introduction  of  a ball  of  chloride  of  calcium  before 
measuring.  If  it  is  not  intended  to  determine  the  carbonic  acid,  this 
operation  is  omitted.  A quantity  of  solution  of  potassa  of  1*4  sp.  gr. 
(1  part  of  dry  hydrate  of  potassa  to  2 parts  of  water),  amounting 
to  from  To  to  -g’o-  of  the  volume  of  the  air,  is  then  introduced 
into  the  measuring  tube  by  means  of  a pipette  with  the  point  bent 
upwards  (fig.  105),  and  spread  over  the  entire  inner  surface  of 
the  tube  by  shaking  the  latter ; when  no  further  diminution  of 
volume  takes  place,  the  decrease  is  read  off.  If  the  air  has 

been  dried  previously  with  chloride  of  calcium,  the  diminution 
of  the  volume  expresses  exactly  the  amount  of  carbonic  acid  j 

contained  in  the  air ; but  if  it  has  not  been  dried  with  chloride  ^ 

of  calcium,  the  diminution  in  the  volume  cannot  afford  correct  ®‘ 
information  as  to  the  amount  of  the  carbonic  acid,  since  the  strong  solu- 
tion of  potassa  absorbs  aqueous  vapor. 

3.  When  the  carbonic  acid  has  been  removed,  a solution  of  pyrogallic 
acid,  containing  1 grm.  of  the  acid  * in  5 or  6 c.  c.  of  water,  is  introduced 
into  the  same  measuring  tube  by  means  of  another  pipette,  similar  to  the 
one  used  in  2 (fig.  105);  the  quantity  of  pyrogallic  acid  employed  should 
be  half  the  volume  of  the  solution  of  potassa  used  in  2.  The  mixed  fluid 
(the  pyrogallic  acid  and  solution  of  potassa)  is  spread  over  the  inner 
surface  of  the  tube  by  shaking  the  latter,  and,  when  no  further  diminu- 
tion of  volume  is  observed,  the  residuary  nitrogen  is  measured. 

4.  The  solution  of  pyrogallic  acid  mixing  with  the  solution  of  potassa  of 
course  dilutes  it,  causing  thus  an  error  from  the  diminution  of  its  tension ; 
but  this  error  is  so  trifling  that  it  has  no  appreciable  influence  upon  the 
results;  it  may,  besides,  be  readily  corrected,  by  introducing  into  the  tube, 
after  the  absorption  of  the  oxygen,  a small  piece  of  hydrate  of  potassa  cor- 
responding to  the  amount  of  water  in  the  solution  of  the  pyrogallic  acid. 

5.  There  is  another  source  of  error  in  this  method  ; viz.,  on  account  of 
a portion  of  the  fluid  always  adhering  to  the  inner  surface  of  the  tube, 
the  volume  of  the  gas  cannot  be  read  off  with  absolute  accuracy.  In 
comparative  analyses,  the  influence  of  this  defect  upon  the  results  may 
be  almost  entirely  neutralized,  by  taking  nearly  equal  volumes  of  air  in 
the  several  analyses,  j* 

6.  Notwithstanding  these  sources  of  error,  the  results  obtained  by  this 
method  are  very  accurate  and  constant.  In  eleven  analyses  which  v. 
Liebig  reports,  the  greatest  difference  in  the  amount  of  oxygen  found 
was  between  20*75  and  21*03.  The  numbers  given  express  the  actual 
and  uncorrected  results. 

* Liebig  has  described  a very  advantageous  method  of  preparing  pyrogallio 
acid.  See  Annal.  d.  Chem.  u.  Pharm.  101,  47. 

\ Bunsen  employs  for  the  absorption  of  oxygen  a papier-mache  ball  saturated 
with  a concentrated  alkaline  solution  of  pyrogallate  of  potassa,  which  he  intro- 
duces into  the  gaseous  mixture  attached  to  a platinum  wire.  By  adopting  this 
proceeding,  the  source  of  error  mentioned  in  5 is  avoided.  See  also  Russell, 
Jour  Chem.  Soc.  1868,  pp.  130,  131. 


PART  III. 

v 

EXERCISES  FOR  PRACTICE. 


36 


EXERCISES  FOR  PRACTICE. 


The  principal  point  kept  in  view  in  the  selection  of  these  exercises  has 
been  that  most  of  them,  and  more  particularly  the  first,  should  permit  an 
exact  control  of  the  results.  This  is  of  the  utmost  importance  for 
students,  since  a well-grounded  self-reliance  is  among  the  most  indispen- 
sable requisites  for  a successful  pursuit  of  quantitative  investigations, 
and  this  is  only  to  be  attained  by  ascertaining  for  one’s  self  how  near  the 
results  found  approach  the  truth. 

Now  a rigorously  accurate  control  is  practicable  only  in  the  analysis 
of  pure  salts  of  known  composition,  or  of  mixtures  composed  of  definite 
proportions  of  pure  bodies.  When  the  student  has  acquired,  in  the 
analysis  of  such  substances,  the  necessary  self-reliance,  he  may  proceed  to 
the  analysis  of  minerals  or  products  of  industry  in  which  such  rigorous 
control  is  unattainable. 

The  second  point  kept  in  view  in  the  selection  of  these  exercises,  has 
been  to  make  them  comprise  both  the  more  important  analytical  methods 
and  the  most  important  bodies,  so  as  to  afford  the  student  the  oppor- 
tunity of  acquiring  a thorough  knowledge  of  every  branch  of  quantitative 
analysis. 

Organic  analysis  offers  less  variety  than  the  analysis  of  inorganic  sub- 
stances ; the  exercises  relating  to  the  former  branch  are  therefore  less 
numerous  than  those  relating  to  the  latter. 

I would  advise  the  student  to  analyze  the  same  substance  repeatedly, 
until  the  results  are  quite  satisfactory.  [It  is  a good  habit  always  to 
carry  on  together  duplicate  analyses.  It  requires  but  little  more  time 
to  make  two  analyses  than  to  make  one,  and  the  operator’s  experience  is 
thus  very  economically  doubled.] 

It  is  by  no  means  necessary  for  the  student  to  go  through  the  whole 
of  these  examples ; the  time  which  he  may  require  to  attain  proficiency 
in  analysis  depends,  of  course,  upon  his  own  abilities.  One  may  be  a good 
analyst  without  having  tried  every  method,  or  determined  every  body. 
A few  substances  well  analyzed  yield  more  profit  than  can  be  obtained 
from  going  over  many  processes  in  a superficial  manner. 

Finally,  the  student  is  warned  against  prematurely  attempting  to  dis- 
cover new  methods ; he  should  wait  until  he  has  attained  a good  degree 
of  proficiency  in  general  chemistry,  and  more  particularly  in  practical 
analysis. 


EXERCISES. 


A.  SIMPLE  DETERMINATIONS  IN  THE  GRAVIMETRIC  WAY,  INTENDED 
TO  PERFECT  THE  STUDENT  IN  THE  PRACTICE  OF  THE  MORE 
COMMON  ANALYTICAL  OPERATIONS. 

[We  give  here,  in  the  first  place,  quite  full  details  of  all  the  steps  in  the 
estimation  of  chlorine  in  chloride  of  sodium,  including  the  preparation 
of  this  salt  in  a state  of  purity.  This,  it  is  hoped,  will  relieve  much  of 
the  perplexity  which  the  beginner  must  at  first  experience  in  making 
out  a scheme  of  operations  from  the  various  separate  paragraphs  where 
the  processes  are  described.  The  student  should  not  fail,  however,  to 
study  carefully  the  chapter  on  operations  while  carrying  on  the  analysis, 
nor  to  examine  every  reference. 

1.  Chloride  of  Sodium. 

Preparation . — Dissolve  150  grm.  of  clean  crystallized  carbonate  of 
soda  in  hot  water,  place  a small  bit  of  litmus  paper  in  the  solution,  add 
pure  hydrochloric  acid  to  acid  reaction,  and  evaporate  in  a porcelain  dish 
to  dryness,  whereby  silica  becomes  insoluble.  If  the  dry  residue  has  a 
yellow  tinge,  which  is  due  to  iron,  raise  the  heat  somewhat  until  the 
residue  is  brown  or  black  in  color  and  no  acid  odor  is  perceptible  when  it 
is  breathed  on.  This  treatment  converts  soluble  sesquichloride  of  iron 
into  insoluble  oxychloride.  Dissolve  the  residue  in  hot  water,  filter,  and 
evaporate  the  solution,  contained  in  a beaker,  at  a temperature  somewhat 
below  the  boiling  point,  until  there  remains  a small  quantity  of  liquid 
above  the  crystals  of  salt.  Pour  off  this  mother  liquor,  rinse  the  crystals 
repeatedly  with  small  quantities  (their  own  bulk)  of  cold  water  until  the 
rinsings  give  but  a very  slight  * reaction  for  sulphuric  acid  with  chloride 
of  barium. 

A portion  \ of  the  salt  thus  obtained  is  crushed  to  a coarse  powder, 
heated  in  a covered  crucible  until  it  ceases  to  decrepitate,  but  not  to 
fusion,  and  preserved  in  a weighing  tube  (like  a small  test  tube,  but  not 
flared  at  the  mouth)  that  is  closed  with  a soft,  well-fitting,  and  smooth 
cork. 

Estimation  of  Chlorine. 

1.  Weighing  out  the  substance. — The  tube  containing  the  prepared 
salt  is  wiped,  if  need  be,  from  dust.  The  cork  is  taken  out,  and  by 
means  of  a bit  of  thin  paper,  or  a clean  linen  handkerchief,  any  particles 


* It  is  not  needful  for  ordinary  quantitative  purposes  that  a salt  should  be 
so  free  from  foreign  matters  that  the  latter  cannot  be  detected  by  sensitive  re- 
agents, and  for  the  reason  that  it  is  not  possible  to  collect  and  weigh  the  minute 
traces  which  are  thus  indicated. 

f Pure  chloride  of  sodium  is  needed  in  other  analyses,  and  the  chief  part  of 
what  is  thus  prepared  should  be  carefully  bottled  and  reserved  for  future  use. 


EXERCISES  FOR  PRACTICE. 


565 


of  salt  adhering  to  the  cork,  and  to  the  inside  of  the  tube  as  far  as  the 
cork  reaches,  are  removed.  The  cork  is  replaced,  and  the  whole  is 
weighed  (see  §§  9 and  10),  the  weight  being  immediately  recorded  in  the 
note-book.  A clean  beaker  or  assay-flask,  of  about  200  c.  c.  capacity, 
being  ready,  the  weighing-tube  is  held  over  it  and  the  cork  carefully 
removed.  A portion  of  substance  is  allowed  to  fall  in  the  vessel,  and, 
the  cork  being  replaced,  the  tube  is  again  counterpoised.  If  two  to  three 
decigrammes  have  been  emptied,  the  operator  is  ready  to  proceed.  If 
less,  more  should  be  transferred  from  the  tube  to  the  vessel.  If  more, 
or  much  more,  it  is  better  to  begin  anew,  by  weighing  off  another  portion 
into  another  beaker  or  flask.  In  this  manner  weigh  off  two  portions  in 
separate  vessels,  so  as  to  carry  together  duplicate  analyses.  Now  affix  a 
piece  of  gummed  paper  to  each  vessel,  and  label  them  to  correspond  with 
their  designation  in  the  note-book. 

2.  Solution  and  precipitation. — Dissolve  the  weighed  portions,  each  in 
about  100  c.  c.  of  cold  distilled  water,  add  a few  drops  of  pure  nitric  acid, 
and,  lastly,  clear  solution  of  nitrate  of  silver  * until  farther  addition  no 
longer  produces  a precipitate. 

Agitate  the  mixture  well,  but  with  care  to  avoid  loss.  This  can  be 
done  by  shaking,  if  a flask  be  in  use,  or  by  stirring  with  a glass  rod,  if  a 
beaker  be  employed. 

Set  the  vessel  aside  in  a dark  place,  covered  with  paper  or  a watch- 
glass  to  exclude  dust,  and  let  stand  for  about  12  hours,  or  until  the 
precipitate  has  subsided  and  the  liquid  above  it  is  perfectly  clear,  then 
add  a drop  of  nitrate  of  silver  to  make  sure  that  the  precipitation  is  com- 
plete (if  not  complete,  add  more  solution  of  silver,  and  let  stand  again 
for  some  hours).  % 

3.  Filtration. — A filter  is  placed  in  a funnel  at  least  % inch  deeper 
than  itself,  and  moistened  with  water,  at  the  same  time  being  carefully 
pressed  down  so  that  its  edges  touch  the  glass  at  all  points.  The  funnel 
being  supported  on  a stand,  a clean  beaker  or  flask  is  put  beneath  it,  and 
the  operator  proceeds  to  pour  the  liquid — on  whose  surface  some  particles 
of  chloride  of  silver  usually  float — into  the  filter,  leaving  the  bulk  of  the 
precipitate  undisturbed.  To  do  this  without  loss  the  following  precau- 
tions may  be  regarded : a.  Touch  the  edge  or  lip  of  the  vessel  with  a 
very  slight  .coat  of  tallow  (a  small  bit  of  which  is  kept  at  hand  under 
the  edge  of  the  work-table,  and  is  applied  with  the  finger),  b.  Pour  slowly 
over  the  greased  place,  along  a glass  rod  held  nearly  vertical,  so  directing 
the  stream  that  it  shall  strike  against  the  side,  not  into  the  vertex  of  the 
filter,  c.  When  the  filter  is  filled  to  within  £ inch  of  the  top  discontinue 
the  pouring,  bringing  the  rod  into  the  vessel  containing  the  precipitate, 
after  it  has  drained  so  that  nothing  will  fall  from  it. 

The  pouring-rod  may  be  simply  straight,  and  an  inch  longer  than  the  diagonal 
of  the  vessel,  or,  when  it  is  desirable  not  to  disturb  a precipitate,  it  may  be  3 — I 
inches  long  and  bent  syphon  fashion  so  as  to  hang  on  the  edge  of  a beaker  or  flask. 
In  either  case  its  end  should  be  rounded  by  fusion,  and  those  portions  along  which 
the  liquid  flows  must  not  be  handled. 

The  vessel  containing  the  precipitate,  as  well  as  that  which  receives 
the  filtrate,  and  likewise  the  funnel,  should  be  kept  covered  as  much  as 


* Solution  of  a silver  coin  in  nitric  acid  answers  for  this  purpose  as  well  as  pure 
nitrate,  provided  it  be  clear  and  contain  but  little  free  acid. 


566 


EXERCISES  FOR  PRACTICE. 


possible  in  all  cases  when  nicety  is  required,  to  prevent  access  of  dust, 
insects,  &c. 

The  most  convenient  covers  are  large  watch-glasses,  but  square  plates  of  glass, 
or  even  cards,  will  generally  answer.  The  receiving-vessel  may  also  be  protected 
by  employing  the  filter-stand  represented  in  fig.  34,  p.  57. 

The  filtration  of  chloride  of  silver  should  be  conducted  without  expos- 
ing it  to  strong  light,  whereby  it  is  blackened,  with  loss  of  chlorine,  p.  208. 

d.  When  all,  or  nearly  all,  the  liquid  has  passed  the  filter,  it  remains 
to  wash  and  to  transfer  the  precipitate. 

These  operations  may  be  carried  on  as  follows:  pour  about  100  c.  c. 
of  cold  distilled  water  upon  the  precipitate,  which  mostly  remains  in  the 
vessel  where  it  was  formed,  and  agitate  vigorously,  in  order  to  break  up 
and  divide  the  lumpy  chloride  of  silver,  and  bring  every  part  of  it  per- 
fectly in  contact  with  the  water. 

When  in  a beaker,  the  agitation  must  be  made  with  great  caution,  by  means 
of  a glass  stirring-rod ; when  in  a narrow-mouthed  flanged  flask,  this  may  be 
tightly  closed  by  a perfectly  smooth  cork  (softened  for  the  purpose  by  squeezing) 
and  then  shaken  violently. 

The  water  and  precipitate  are  now  poured  together  upon  the  filter, 
with  the  precautions  before  detailed.  The  last  portions  of  the  precipitate 
are  removed  from  the  beaker  or  flask  by  repeated  rinsings,  in  which  a 
wash-bottle  like  fig.  36,  p.  59,  may  be  conveniently  employed. 

Any  portions  of  precipitate  that  adhere  to  the  sides  of  the  vessel  too 
strongly  to  be  removed  by  a stream  from  the  wash-bottle  must  be  rubbed 
off.  For  this  purpose  the  feather  is  employed. 

It  is  made  from  a goose-quill,  by  cutting  off  the  extreme  tip  for  an  inch  or  so, 
and  smoothly  trimming  away  the  beard,  except  a portion  of  one  half-inch  in  length 
on  the  inside  of  the  curve.  The  tubular  part  may  be  removed  or  not,  to  suit  the 
depth  of  the  dish  which  is  to  be  washed. 

The  dish  being  wiped  clean,  externally,  a little  water  is  put  in  it,  and, 
it  being  held  up  to  the  light,  its  whole  interior  surface  is  gently  rubbed 
with  the  feather,  then  rinsed,  rubbed  again  and  rinsed,  so  long  as  careful 
inspection  discovers  any  portions  of  adhering  precipitate  ; finally,  the 
feather  is  rinsed  in  a stream  of  water,  the  rinsings  in  each  case  being 
poured  upon  the  filter. 

The  washing  is  now  continued  by  help  of  the  wash-bottle.  A jet  of 
cold  water  is  directed,  first,  upon  the  interior  of  the  funnel,  just  above 
the  filter,  then  upon  the  edge  of  the  filter  itself.  If  thrown  immediately 
against  the  paper,  this  is  liable  to  be  perforated.  The  stream  of  water  is 
carried  around  the  edge  of  the  filter  until  the  latter  is  nearly  full,  and 
the  liquid  is  then  allowed  to  drain  off.  This  process  is  repeated  until  a 
portion  of  the  wash-waters,  collected  to  the  depth  of  an  inch  in  a test 
tube  containing  a drop  of  hydrochloric  acid,  give  no  turbidity  of  chlo- 
ride of  silver.  When  this  is  accomplished,  the  precipitate  is  washed 
down  into  the  vertex  of  the  filter.  The  funnel  is  then  closely  covered 
with  paper  (p.  62),  labelled,  allowed  to  drain  thoroughly,  and  set  away 
in  a warm  place  for  drying. 

When  the  Bunsen  pump  is  employed,  read  § 53  c.  p.  77,  and  follow  the 
directions  on  page  72,  bottom;  as  to  washing,  see  pp.  67  and  68. 

5.  Drying  the  filter.  In  public  laboratories  a heated  closet  is  usually 
provided  for  drying  filters.  Its  temperature  should  not  exceed  100°  C, 


EXERCISES  FOR  PRACTICE. 


567 


In  default  of  such  special  arrangement,  the  drying  may  he  effected  over 
the  register  of  a hot-air  furnace,  or  over  a common  stove  or  kitchen  range. 

The  funnel  may  also  be  supported  on  a retort-stand  over  a sheet  of 
iron,  which  is  heated  beneath  by  a lamp,  or  may  be  placed  at  once  in  the 
water-bath.  See  pp.  62  and  79. 

6.  When  the  precipitate  is  perfectly  dry  we  proceed  to  ignite  it  for 
weighing. 

A small  porcelain  crucible  (platinum  must  not  be  used)  is  cleaned, 
gently  ignited,  and  when  cool  (after  15 — 20  minutes)  weighed. 

The  work-table  being  clean,  two  small  sheets  of  fine  and  smooth  writ- 
ing or  glazed  paper  are  opened  and  laid  down  side  by  side.  The  filter 
is  removed  from  the  funnel  and  carefully  inverted  upon  one  of  the 
papers.  The  precipitate  is  loosened  from  the  filter  by  squeezing  and 
rubbing  gently  between  the  fingers,  and  when  it  has  mostly  separated 
the  filter  is  lifted,  reversed,  and  any  portions  of  chloride  of  silver  still 
adhering  are  loosened  by  rubbing  its  sides  together.  What  is  thus  de- 
tached is  poured  or  shaken  out  on  the  paper. 

The  filter  is  now  spread  out  as  a half-circle  upon  the  other  sheet  of 
paper,  and,  beginning  with  the  straight  edge,  is  folded  up  into  a narrow 
flattened  roll,  the  two  ends  of  which  are  then  brought  together.  In  this 
way  those  central  portions  of  the  filter  to  which  particles  of  precipitate 
adhere  are  thoroughly  enveloped  by  the  exterior  parts,  so  that  in  the  sub- 
sequent burning  nothing  can  easily  escape. 

The  crucible  being  placed  on  the  glazed  paper,  the  filter  is  taken  by 
the  two  free  ends  in  a clean  pincers  or  tongs,  put  to  the  flame  of  a lamp 
to  set  it  on  fire,  and  then  held  over  the  crucible  until  it  is  completely 
charred.  It  is  then  dropped  into  the  crucible,  and  moistened  with  two 
or  three  drops  of  nitric  acid.  The  crucible  is  covered  and  placed  over  a 
low  flame  until  its  contents  are  dry,  it  is  then  heated  somewhat  stronger, 
whereby  the  carbon  is  nearly  or  entirely  consumed. 

The  crucible  being  allowed  to  cool,  one  more  drop  of  nitric  acid,  and 
afterwards  a drop  of  hydrochloric  acid,  is  added  to  the  residue,  and  it  is 
heated  cautiously,  without  the  cover,  until  fumes  cease  to  escape.  This 
treatment  with  nitric  acid  serves  to  destroy  carbon  and  convert  any 
reduced  silver  to  nitrate,  which  the  hydrochloric  acid  in  turn  transforms 
into  chloride.  When  the  crucible  is  cool,  it  is  placed  again  on  the  paper, 
and  the  precipitate  is  poured  into  it  from  the  other  sheet,  the  last  par- 
ticles being  detached  by  cautious  tapping  with  the  fingers  underneath,  or 
by  the  use  of  a clean  feather  or  camel’s  hair  pencil. 

The  crucible  is  now  put  over  a low  flame  and  heated  cautiously  until 
the  chloride  of  silver  begins  to  fuse  on  the  edges.  It  is  then  covered  and 
let  cool.  When  cold  it  is  weighed.  Read  § 115,  1,  and  the  references 
there  made. 

7.  Hecord  and  calculation  of  results.  The  amount  of  chloride  of 
silver  is  learned  by  subtracting  from  the  total  the  joint  weight  of  the 
crucible  and  filter-ash.  The  quantity  of  chlorine  is  obtained  by  multi- 
plying the  amount  of  chloride  of  silver  by  the  decimal  0*24724.  In 
order  to  compare  results  they  are  reduced  to  per  cent,  statements  by  the 
following  proportion : — 

Substance  : chlorine  in  substance  : : 100  : chlorine  in  100  ; i.e.  per  cent. 

The  record  may  be  made  as  follows  : It  is  well  to  work  out  the  calculations  in 
full  in  the  weight-book,  as  in  case  of  mistake  the  data  are  at  hand  for  revision. 


568 


EXERCISES  FOR  PRACTICE. 


No.  1. 

No.  2. 

Na  Cl  and  tube 

6*180 

“ “ —substance 

5*765 

Substance 

-435 

•415 

14*3270 

Crucible,  A g Cl  and  Ash 

15*3630 

Cr 

14*298  ) w . nnnr 

13-oo?5|2 * * * * * * * * * * 13'3105 

Ash 

0015  I14'2995 

Ag  Cl 

1*0635 

1*0165 

0*24724 

0*24724 

42540 

40660 

21270 

20330 

74445 

71155 

42540 

40660 

21270 

20330 

Cl 

— *262939740 

•251319460 

•435)  26,29397  (60*44# 

*415)  25,13194  (60*56# 

2610 

2490 

1939 

2319 

1740 

2075 

1997 

2444 

Found. 

Calculated. 

No.  1.  No.  2. 

Chlorine 

60*66 

We  have  here  employed  the  simplest  arithmetical  calculation.  It  is  well  to 
duplicate  the  calculation  with  help  of  the  tables  given  in  the  Appendix.  See 
pp.  462-4. 

The  first  determination  given  above  is  not  only  fair  for  this  method,  but  answers 
all  ordinary  purposes.  The  second  is  very  good,  though  with  care  still  closer 
accordance  with  theory  can  be  easily  attained.  ] 

2.  Iron. 

Procure  10 — 15  grins,  of  fine  bright  pianoforte  wire,  cut  it  into  lengths 

of  about  0*3  grin,  and  keep  it  free  from  rust  in  a dry  bottle. 

Weigh,  on  a watch-glass,  for  each  estimation,  about  0*3  grm.  of  wire, 

and  dissolve  in  hydrochloric  acid,  with  addition  of  nitric  acid.  The  acids 

are  diluted  with  a little  water. 

The  solution  is  effected  by  heating  in  a moderate-sized  beaker  covered 

with  a watch-glass.  When  complete  solution  has  ensued,  and  the  color 

of  the  fluid  shows  that  all  the  iron  is  dissolved  as  sesquioxide  (if  this  is 
not  the  case  some  more  nitric  acid  must  be  added),  rinse  the  watch-glass, 

dilute  the  fluid  to  about  150  c.  c.,  heat  to  incipient  ebullition,  add 
ammonia  in  moderate  excess,  filter  through  a filter  exhausted  with  hydro- 

chloric acid,  &c.  (Comp.  § 113,  1,  a.)  If  Bunsen’s  methods  are  em- 
ployed, proceed  exactly  as  described  on  pp.  72,  73,  and  77. 

As  the  sesquioxide  of  iron  generally  contains  a small  quantity  of  silicic 

acid  (partially  arising  from  the  silicon  in  the  wire,  partially  taken  up 
from  the  glass  vessels),  after  it  is  weighed,  digest  with  fuming  hydro- 
chloric acid  for  some  hours ; when  the  oxide  of  iron  is  all  dissolved,  dilute, 
collect  the  silica  on  a small  filter,  ignite  and  weigh.  The  weight  is  the 
silica  -f-  the  ashes  of  both  filters. 


EXERCISES  FOR  PRACTICE. 


569 


The  records  are  made  as  follows : — 

Watch-glass  -f  iron 10-3192 

“ empty ' 9*9750 

Iron *3442 

Crucible  -f-  sesquioxide  of  iron  + silica  + filter  ash . . 17*0703 

“ empty 16*5761 

•4942 

Ash  of  large  filter *0008 

Sesquioxide  of  iron  + silica *4934 

Crucible  + silica  -f-  ashes  of  both  filters 16*5809 

“ empty 16.5761 

*0048 

Ashes  of  the  filters *0014 

Silica *0034 


*4934  — *0034  = *4900  sesquioxide  of  iron  = *343  iron 
which  gives  99*65  per  cent. 

3.  Acetate  of  Lead. 

Determination  of  Oxide  of  Lead. — Triturate  the  dry  and  non-effio- 
resced  crystals  * in  a porcelain  mortar,  and  press  the  powder  between 
sheets  of  blotting  paper  until  fresh  sheets  are  no  longer  moistened  by  it. 

a.  Weigh  about  1 grm.,  dissolve  in  water,  with  addition  of  a few  drops 
of  acetic  acid,  and  proceed  exactly  as  directed  § 116,  1,  a. 

b.  Weigh  about  1 grm.,  and  proceed  exactly  as  directed  § 116,,  5. 


PbO 111*50  58*84 

A 51*00  26*91 

3 aq 27*00  14*25 


189*50  100*00 

4.  Potash  Alum. 

Determination  of  Alumina. — Press  pure  triturated  potash  alum  be- 
tween sheets  of  blotting  paper ; weigh  off  about  2 grm.,  dissolve  in  water, 
and  determine  the  alumina  as  directed  § 105,  a. 


KO 47*11  9*93 

A1A 51*50  10*85 

4 S03 160*00  33*71 

24  HO 216*00  45*51 


474*61  100*00 


* Obtained  by  dissolving  the  pulverized  commercial  salt  in  hot  water  nearly  to 
saturation,  filtering,  adding  a drop  or  two  of  acetic  acid  to  the  solution,  and 
slowly  evaporating  to  crystallization. 


570 


EXERCISES  FOR  PRACTICE. 


5.  Bichromate  of  Potash. 

Determination  of  Chromium. — Fusje  pure  bichromate  of  potash  at  a 
gentle  heat,  weigh  off  *4 — -6  grin.,  dissolve  in  water,  reduce  with  hydro- 
chloric acid  and  spirit  of  wine,  and  proceed  as  directed  § 130,  I.  a,  a. 


KO 47*11  31-92 

2 Cr  03 100-48  68*08 


147-59  100-00 

6.  Arsenious  Acid. 

Dissolve  about  0*2  grin,  pure  arsenious  acid  in  small  lumps  in  a 
middle-sized  flask,  with  a glass  stopper,  in  some  solution  of  soda,  by 
digesting  on  the  water-bath ; dilute  with  a little  water,  add  hydrochloric 
acid  in  excess,  and  then  nearly  fill  the  flask  with  clear  sulphuretted 
hydrogen  water.  Insert  the  stopper  and  shake.  If  the  sulphuretted 
hydrogen  is  present  in  excess,  the  precipitation  is  terminated ; if  not, 
conduct  an  excess  of  sulphuretted  hydrogen  gas  into  the  fluid ; proceed 
in  all  other  respects  exactly  as  directed  § 127,  4. 


As 75  75-76 

03  24  24-24 


99  100-00 


B.  COMPLETE  ANALYSIS  OF  SALTS  IN  THE  GRAVIMETRIC  WAY; 

CALCULATION  OF  THE  FORMULAE  FROM  THE  RESULTS  OBTAINED. 

(§§  202,  203.) 

7.  Carbonate  of  Lime. 

Heat  pure  eaTbonate  of  lime  in  powder  (no  matter  whether  Iceland 
spar  or  the  artificially  prepared  substance,  see  “ Qual.  Anal.,”  Am.  Ed., 
p.  83)  gently  in  a platinum  crucible. 

a.  Determination  of  Dime. — Dissolve  in  a covered  beaker,  about  1 
grm.  in  dilute  hydrochloric  acid,  heat  gently  until  the  carbonic  acid  is 
completely  expelled,  and  determine  the  lime  as  directed  § 103,  2,  5,  a. 

b.  Determination  of  Carbonic  Acid. — Determine  in  about  0‘8  grm.  the 
(Carbonic  acid  after  § 139,  II.,  c?,  cc. 


(CaO 28  56-00 

fC02 22  44-00 


50  100-00 

8.  Sulphate  of  Copper. 

Triturate  the  pure  crystals*  in  a porcelain  mortar,  and  press  the  powder 
'between  sheets  of  blotting  paper. 

* [Boil  a solution  of  commercial  blue  vitriol  with  a little  pure  binoxide  of  lead 
(see  “ Qual.  Anal.,”  Am.  Ed.,  p.  58),  to  sesquioxidize  the  iron,  then  with  a little 
carbonate  of  baryta,  to  precipitate  it,  filter  and  crystallize.  H.  Wurtz,  Am. 
Jour.  (2),  XXVI.  367.Q 


EXERCISES  FOR  PRACTICE. 


571 


a.  Determination  of  Water  of  Crystallization. — 1.  Weigh  off  in  a 
crucible  1 — 2 grm.  of  the  salt,  and,  having  first  heated  the  air-bath  (Fig. 
22,  p.  39)  so  that  the  thermometer  stands  steadily  at  120° — 140°,  intro- 
duce the  crucible,  uncovered,  and  maintain  the  heat  for  two  hours. 
Then  cool  the  crucible  in  a desiccator  and  weigh.  Heat  again  as  before, 
for  an  hour,  and  weigh.  If  need  be,  repeat  the  heating  until  no  more 
loss  occurs.  The  loss  expresses  the  amount  of  water  expelled  at  the 
temperature  of  140°,  or  four  equivalents.  2.  Raise  the  temperature  of 
the  air-bath  to  between  250° — 260°  and  proceed  as  before.  The  loss  is 
the  one  equivalent  of  strongly  combined  water  of  crystallization,  or,  as 
some  term  it,  water  of  halhydration. 

b.  Determination  of  Sulphuric  Acid. — In  another  portion  of  the  sul- 
phate of  copper  (about  1*5  grm.)  determine  the  sulphuric  acid  according 
to  §132,1,1. 

d.  Determination  of  Oxide  of  Copper. — In  about  1*5  grm.  determine 
the  oxide  of  copper  as  directed  § 119,  1,  a,  a. 


CuO 39*70  31*83 

S03 40*00  32*08 

HO 9*00  7*22 

4aq 36*00  28*87 


124*70  100*00 


9.  Crystallized  Phosphate  of  Soda. 

a.  Determination  of  the  Water  of  Crystallization. — Heat  about  I 
grm.  of  the  pure  uneffloresced  salt  in  a platinum  crucible,  slowly  and 
moderately,  first  in  the  water-bath,  then  in  the  air-bath,  and  finally  some 
distance  above  the  lamp  (not  to  visible  redness) ; the  loss  of  weight  gives 
the  amount  of  water  of  crystallization. 

b.  Determination  of  the  Water  of  Constitution. — Ignite  the  residue 
of  a. 

c.  Determination  of  Phosphoric  Acid. 

a.  Treat  1*5 — 2 grm.  of  the  salt  as  directed  § 134,  5,  a. 

13.  Treat  about  1 grm.  of  the  salt  after  § 134,  c. 

y.  Treat  about  0*2  grm.  of  the  salt  as  directed  § 134,  b , j3, 

I recommend  the  student  to  perform  the  determination  by  each  of 
these  methods,  as  they  are  all  in  common  use  in  the  analytical  labora- 
tory* 

d.  Determination  of  Soda. — Treat  about  1*5  grm.  of  the  salt  according 
to  § 135,  <z,  a.  After  the  excess  of  lead  has  been  separated  with  hydro- 
sulphuric  acid,  the  fluid  is  to  be  evaporated  to  dryness  and  weighed  in  a 
platinum  dish;  comp.  § 69,  6,  and  § 98,  2. 


P06 71*00  19*83 

2NaO 62*00  17*32 

HO 9*00  2*51 

24  aq 216*00  60*34 


358*00  100*00 

10.  Chloride  of  Silver. 

Ignite  pure  fused  chloride  of  silver  in  a stream  of  pure  dry  hydrogen 


572 


EXERCISES  FOR  PRACTICE. 


till  complete  decomposition  is  effected,  and  weigh  the  silver  obtained. 
The  ignition  may  be  performed  in  a light  bulb  tube,  or  in  a porcelain 
boat  in  a glass  tube,  or  in  a porcelain  crucible  with  perforated  cover 
(§  H5,  4). 

The  chlorine  may  be  in  this  case  estimated  by  difference  ; if  you  want 
to  determine  it  directly,  proceed  as  directed  § 141,  II.,  b. 

Ag 107-97  75-28 

Cl 35*40  24-72 


143-43  100-00 

11.  Sulphide  of  Mercury. 

Reduce  to  a fine  powder,  and  dry  at  100°. 

a.  Determination  of  Sulphur. — Treat  about  0*5  grm.,  as  directed  § 148, 
/?,  p.  326,  using  nitric  acid  and  chlorate  of  potassa.  Precipitate  with 
chloride  of  barium,  and  after  decanting  the  clear  liquid  into  a filter,  boil 
the  sulphate  of  baryta  twice  with  dilute  solution  of  acetate  of  ammonia, 
and  finally  wash  with  hot  water. 

b.  Determination  of  Mercury. — Dissolve  about  0*5  grm.  as  before, 
dilute,  and  allow  to  stand  in  a moderately  warm  place  until  the  smell  of 
chlorine  has  nearly  gone  off ; filter  if  necessary,  add  ammonia  in  excess, 
heat  gently  for  some  time,  add  hydrochloric  acid  until  the  white  pre- 
cipitate of  chloride  of  mercury  and  amide  of  mercury  is  redissolved,  and 
treat  the  solution,  which  now  no  longer  smells  of  chlorine,  as  directed 


118,  3. 

Hg 100.00  86-21 

S 16-00  13-79 


116-00  100-00 

12.  Crystallized  Sulphate  of  Lime. 

Select  clean  and  pure  crystals  of  selenite,  triturate,  and  dry  under  the 
desiccator  (§  27). 

a.  Determination  of  Water. — After  § 35,  a,  a. 

b.  Determination  of  Sulphuric  Acid  and  Dime  (§  132,  II.,  b}  a). 


CaO 28  32-56 

S03 40  46-51 

2 aq 18  20*93 


86  100-00 


0.  SEPARATION  OF  TWO  BASES  OR  TWO  ACIDS  FROM  EACH  OTHER, 
AND  DETERMINATIONS  IN  THE  VOLUMETRIC  WAY. 

13.  Separation  of  Iron  from  Manganese. 

Dissolve  in  hydrochloric  acid  about  0’2  grm.  fine  pianoforte  wire,  and 
about  the  same  quantity  of  ignited  protosesquioxide  of  manganese  (pre- 
pared as  directed  § 109,  1 a)\  heat  with  a little  nitric  acid,  and  separate 
the  two  metals  by  means  of  acetate  of  soda  (p.  363,  70).  Determine  the 
manganese  as  directed  § 109,  3. 


EXERCISES  FOR  PRACTICE. 


573 


14.  Volumetric  Determination-  of  Iron  by  Solution  of 
Permanganate  of  Potassa. 

a.  Graduation  of  the  Solution  of  Permanganate  of  Potassa. 

a.  By  metallic  iron  (fine  piano  wire).  0*2  grm.  to  be  dissolved  in 
dilute  sulphuric  acid  (p.  194).  Use  the  iron  wire,  a portion  of  which  has 
been  analyzed  in  Exercise  2,  and  correct  for  impurities  accordingly. 

(3.  By  oxalate  of  ammonia.  0*2 — 0*3  grm.  to  be  weighed  off  (p. 
196). 

b.  Determination  of  the  Protoxide  of  Iron  in  double  Sulphate  of 
Protoxide  of  Iron  and  Ammonia. 

a.  In  solution  acidified  with  sulphuric  acid  (p.  197,  J3). 

(3.  In  solution  acidified  with  hydrochloric  acid  (p.  198,  note). 

The  formula  requires  18*37  per  cent,  of  Fe  O. 

c.  Determination  of  the  Iron  in  a Limonite. 

Powder  finely,  dry  at  100°,  weigh  off  2 grm.,  heat  with  strong  hydro- 
chloric acid  till  the  sesquioxide  of  iron  is  completely  dissolved,  dilute, 
filter,  make  the  solution  up  to  200  c.  c.,  and  mix.  In  20  c.  c.  of  this  so- 
lution determine  the  iron  after  § 113,  3,  a,  p.  203.  Reserve  half  of  the 
solution  for  the  next  exercise  (see  also  p.  524). 

15.  Volumetric  Determination  of  Iron  with  Hyposulphite  of 

Soda. 

a.  Graduation  of  the  Solution  of  Hyposulphite  of  Soda. 

a.  By  solution  of  sesquichloride  of  iron  (p.  204). 

0.  By  ammonia-iron-alum  (p.  204). 

b.  Determination  of  Iron  in  Limonite. 

Use  20  c.  c.  of  the  solution  obtained  in  Exercise  14,  c.,  after  making 

y y o 

sure  that  the  iron  all  exists  in  the  state  of  sesquioxide  (see  p.  192,  1,  a.) 

16.  Determination  of  Nitric  Acid  in  Nitrate  of  Potassa. 

Heat  pure  nitre,  not  to  fusion,  and  transfer  it  to  a tube  provided  with 
a cork. 

a.  Treat  0*5  grm.  as  directed  p.  329,  P. 

b.  In  0*2  to  0*3  grm.,  estimate  nitric  acid  according  to  p.  330,  <7,  a. 

KO 47*11 46*59 

NO, 54*00 53*41 


101*11 100*00 

17.  Separation  of  Magnesia  from  Soda. 

Dissolve  about  0*4  grm.  pure  recently  ignited  magnesia*  and  about 
0*5  grm.  pure  well-dried  chloride  of  sodium  in  dilute  hydrochloric  acid 


This  may  be  prepared  according  to  19,  p.  345. 


574 


EXERCISES  FOR  PRACTICE. 


(avoiding  a large  excess),  and  separate  with  oxalic  acid,  after  p.  345, 

16, 

18.  Separation  of  Potash  from  Soda. 

Triturate  crystallized  tartrate  of  potassa  and  soda  (Rochelle  salt), 
press  between  blotting  paper,  weigh  oft’  about  1*5  grm.,  heat  in  a plati- 
num crucible,  gently  at  first,  then  for  some  time  to  gentle  ignition.  The 
carbonaceous  residue  is  first  extracted  with  water,  finally  with  dilute 
hydrochloric  acid,  the  acid  fluid  is  evaporated  in  a weighed  platinum 
dish,  and  the  chlorides  are  weighed  together  (§  97, 3).  Then  separate 
them  by  bichloride  of  platinum  (p.  339,  1),  and  calculate  from  the 
results  the  quantities  of  soda  and  potassa  severally  contained  in  the 
Rochelle  salt. 


KO 

47-11 

16-70 

NaO 

31-00 

10-99 

C8HAo 

132-00 

46-79 

8 aq 

72-00 

25-52 

282-11 

100-00 

19.  Volumetric  Determination  of  Chlorine  in  Chlorides. 

a.  Preparation  and  examination  of  the  solution  of  nitrate  of  silver 
(§  141.  I.,  b.  a). 

b.  Indirect  determination  of  the  soda  and  potassa  in  Rochelle  salt,  by 
volumetric  estimation  of  the  chlorine  in  the  alkaline  chlorides  prepared 
as  in  No.  18.  For  calculation,  see  § 197,  a (p.  465). 

20.  Separation  of  Zinc  from  Cadmium. 

Dissolve  in  hydrochloric  acid  about  0*4  grin,  of  pure  oxide  of  cad- 
mium, and  about  the  same  quantity  of  pure  oxide  of  zinc,  both  recently 
ignited,  and  separate  the  metals  as  directed  p.  376,  95* 

21.  Acidimetry. 

a.  Preparation  of  standard  sulphuric  acid  and  solution  of  soda. 
(§  204,  a.)  pp.  490-493. 

b.  Determination  of  acid  in  hydrochloric  acid,  by  the  specific  gravity 

(p-487)- 

c.  Determination  of  acid  in  the  same  hydrochloric  acid,  by  an  alkaline 
fluid  of  known  strength  (p.  494). 

d.  Determination  of  acid  in  colored  vinegar,  by  saturation  with  a 
standard  alkaline,  solution.  (Application  of  test  papers,  p.  496.  /?.) 

e.  Preparation  of  an  ammoniacal  solution  of  sulphate  of  copper  (§  205) ; 
determination  of  its  strength  by  normal  sulphuric  acid ; estimation  of 
the  acid  in  the  hydrochloric  acid  used  in  c and  <7,  by  means  of  the  cop- 
per solution ; in  this  latter  process  the  student  may  also  add  to  the 
hydrochloric  acid  some  neutral  sulphate  of  zinc. 

22.  Alkalimetry. 

a.  Preparation  of  the  test  acid  after  Descroizilles  and  Gay-LussAO^ 
(§  207). 


EXERCISES  FOR  PRACTICE. 


575 


b.  Valuation  of  a soda-ash  after  expulsion  of  the  water  by  gentle 
ignition. 

a.  After  Descroizilles  and  Gay-Lussac  (p.  499). 

13.  After  Mohr  (p.  500). 

23.  Determination  of  Ammonia. 

Treat  about  0*8  grm.  chloride  of  ammonium  as  directed  § 99,  3,  a. 

NH4C1..  18-00...  33-67  NH2 17*00...  31-80 

Cl 35-46...  66-33  HC1 36*46...  68*20 


53-46  100-00  53-46  100*00 

24.  Separation  of  Iodine  from  Chlorine. 

Dissolve  about  0*5  grm.  pure  iodide  of  potassium  and  about  2 — 3 
grm.  pure  chloride  of  sodium  to  250  c.  c.,  and  determine  the  iodine  and 
chlorine  : — 

a.  In  50  c.  c.,  after  § 169,  2,  a (203).  Calculation  § 198,  c. 

b.  In  50  c.  c.,  after  § 169,  2,  b (204). 

c.  In  10  c.  c.,  after  § 169,  2,  c (205). 


D.  ANALYSIS  OF  ALLOYS,  MINERALS,  INDUSTRIAL  PRO- 
DUCTS, ETC.,  IN  THE  GRAVIMETRIC  AND  VOLUMETRIC 
WAY. 

25.  Analysis  of  Brass. 

Brass  consists  of  from  25  to  35  per  cent,  of  zinc  and  from  75  to  65 
per  cent,  of  copper.  It  also  contains  usually  small  quantities  of  tin  and 
lead,  and  occasionally  traces  of  iron. 

Dissolve  about  20  grm.  in  nitric  acid,  evaporate  on  the  water-bath  to 
dryness,  moisten  the  residue  with  nitric  acid,  add  some  water,  warm, 
dilute  still  further,  and  filter  off  any  residual  binoxide  of  tin  (§  126,  1, 
a).  Add  to  the  filtrate,  or,  if  the  quantity  of  tin  is  very  inconsidera- 
ble, directly  to  the  solution,  about  20  c.  c.  dilute  sulphuric  acid ; evapo- 
rate to  dryness  on  the  water-bath,  add  50  c.  c.  water,  and  apply  heat. 
If  a residue  remains  (sulphate  of  lead),  filter  it  off,  and  treat  it  as 
directed  § 116,  3.  In  the  filtrate,  separate  the  copper  from  the  zinc 
by  hyposulphite  of  soda  (p.377,  99).  If  the  quantity  of  iron  present 
can  be  determined,  determine  it  in  the  weighed  oxide  of  zinc  (§  160). 

26.  Analysis  of  Solder  (Tin  and  Lead). 

Introduce  about  1*5  grm.  of  the  alloy,  cut  into  small  pieces,  into  a 
flask,  treat  it  with  nitric  acid,  and  proceed  as  directed  p.  391,  133,  to 
effect  the  separation  and  estimation  of  the  tin. 

Mix  the  filtrate  in  a porcelain  dish  with  pure  dilute  sulphuric  acid, 
evaporate  the  nitric  acid  on  the  water  bath,  and  proceed  with  the  sul- 
phate of  lead  obtained  as  directed  § 116,  3.  Test  the  fluid  filtered  from 
the  sulphate  of  lead  with  sulphuretted  hydrogen  and  sulphide  of  ammo- 
nium for  the  other  metals  which  the  alloy  might  contain  besides  tin 


576 


EXERCISES  FOR  PRACTICE. 


and  lead.  The  binoxide  of  tin  may  contain  small  quantities  of  iron  or 
copper ; it  is  tested  for  these  by  fusion  with  carbonate  of  soda  and  sul- 
phur (p.  389,  /?). 

27.  Analysis  of  a Dolomite. 

See  § 221. 

28.  Analysis  of  Felspar. 

a.  Decomposition  by  carbonate  of  soda  (§  140,  II.,  6.) ; removal  of  the 
silicic  acid ; precipitation  of  the  alumina  together  with  the  small  quantity 
of  sesquioxide  of  iron  by  ammonia  (in  platinum  or  Berlin  porcelain,  not 
in  glass  vessels)  after  § 161,  3 (88)  j separation  of  baryta,  if  present, 
from  the  filtrate  with  dilute  sulphuric  acid,  and  then  of  lime  with  ox- 
alate of  ammonia,  § 154  (23).  Finally,  separation  of  the  alumina  from 
the  sesquioxide  of  iron  generally  present  in  small  quantity  (§  160). 

b.  Decomposition  by  Smith’s  method,  p.  303.  Separate  the  alka- 
lies after  § 152,  1. 

c.  Determined  loss  by  ignition. 

29.  Assay  of  a Calamine  or  Smithsonite. 

After  § 228. 

Volumetric  determination  of  the  zinc. 

30.  Analysis  of  Galena. 

a.  Determination  of  the  sulphur,  lead,  iron,  &c.,  as  directed  § 225. 

b.  Determination  of  the  silver  after  § 226. 

31.  Valuation  of  Chloride  of  Lime  (§  211). 

a.  After  Penot  (p.  505). 

b.  After  Bunsen  (p.  508). — The  solutions  to  be  prepared  and  the 
separated  iodine  to  be  determined  as  directed  § 146  (p.  314). 

32.  Valuation  of  Manganese  (§  214). 

a.  After  Fresenius  and  Will  (p.  509). 

b.  After  Bunsen  (p.  512). 

c.  By  means  of  iron  (p.  512). 

33.  Analysis  of  Gunpowder. 

After  (p.  514). 

E.  DETERMINATION  OF  THE  SOLUBILITY  OF  SALTS. 

34.  Determination  of  the  Degree  of  Solubility  of 
Common  Salt. 

a.  At  boiling  heat.— Dissolve  perfectly  pure  pulverized  chloride  of 
sodium  in  distilled  water,  in  a flask,  heat  to  boiling,  and  keep  in  ebulli- 


EXERCISES  FOR  PRACTICE. 


577 


tion  until  part  of  the  dissolved  salt  separates.  Filter  the  fluid  now  with 
the  greatest  expedition,  through  a funnel  surrounded  with  boiling  water 
and  covered  with  a glass  plate,  into  an  accurately  tared  capacious  mea- 
suring flask.  As  soon  as  about  100  c.  c.  of  fluid  have  passed  into  the 
flask,  insert  the  cork,  allow  to  cool,  and  weigh.  Fill  the  flask  now  up 
to  the  mark  with  water,  and  determine  the  salt  in  an  aliquot  portion  of 
the  fluid,  by  evaporating  in  a platinum  dish  (best  with  addition  of  some 
chloride  of  ammonium,  which  will,  in  some  measure,  prevent  decrepita- 
tion) ; or  by  determining  the  chlorine  (§  141). 

b.  At  14°. — Allow  the  boiling  saturated  solution  to  cool  down  to  this 
temperature  with  frequent  shaking,  and  then  proceed  as  in  a. 

100  parts  of  water  dissolve  at  109*7° ... . 40*35  of  chloride  of  sodium. 
100  “ “ 14°  35*87  “ “ 

35.  Determination  of  the  Degree  of  Solubility  of  Sulphate 

of  Lime. 

«.  At  100°. 
b.  At  12°. 

Digest  pure  pulverized  sulphate  of  lime  for  some  time  with  water,  in 
the  last  stage  of  the  process  at  40 — 50°  (at  which  temperature  sulphate 
of  lime  is  most  soluble)  ; shake  the  mixture  frequently  during  the  pro- 
cess. Decant  the  clear  solution,  together  with  a little  of  the  precipi- 
tate, into  two  flasks,  and  boil  the  fluid  in  one  of  them  for  some  time ; 
allow  that  in  the  other  to  cool  down  to  12°,  with  frequent  shaking, 
and  let  it  stand  for  some  time  at  that  temperature.  Then  filter  both 
solutions,  weigh  the  filtrates,  and  determine  the  amount  of  sulphate  of 
lime  respectively  contained  in  them,  by  evaporating  and  igniting  the 
residues. 

100  parts  of  water  dissolve  at  100° 0*217  of  anhydrous  sulphate  of  lime. 

100  “ “ 12°....  0*233  “ 


F.  DETERMINATION  OF  THE  SOLUBILITY  OF  GASES  IN 
FLUIDS,  AND  ANALYSIS  OF  GASEOUS  MIXTURES. 

36.  Determination  of  the  Absorption-Coefficient  of 
Sulphurous  Acid. 

See  Annal.  d.  Chem.  u.  Pharm.,  vol.  95,  page  1 ; also  § 131,  2. 

37.  Analysis  of  Atmospheric  Air. 

See  §§  240—242. 

G.  ORGANIC  ANALYSIS  AND  DETERMINATIONS  OF  THE 
EQUIVALENTS  OF  ORGANIC  BODIES ; ALSO  ANALYSES 
IN  WHICH  ORGANIC  ANALYSIS  IS  APPLIED. 

38.  Analysis  of  Tartaric  Acid. 

Select  clean  and  white  crystals.  Powder  and  dry  at  100°. 
a.  Burn  with  oxide  of  copper  (§§  174 — -175). 

37 


578 


EXERCISES  FOR  PRACTICE. 


b.  Burn  with  oxide  of  copper  and  finish  with  oxygen  gas  (§  176). 

c.  Burn  in  oxygen  (§  178). 

C8 48  32 

He 6 4 

012 96  64 


150  100 

39.  Determination  of  the  Nitrogen  in  Crystallized  Eerrocyanide 

of  Potassium. 

Triturate  the  perfectly  pure  crystals,  dry  the  powder  in  the  desiccator 
(§  27),  and  determine  the  nitrogen  as  directed  § 185.  The  formula  re- 
quires 19*87  per  cent,  of  nitrogen. 

40.  Analysis  of  Uric  Acid  (or  any  other  perfectly  pure  organic 
compound  of  carbon,  hydrogen,  oxygen,  and  nitrogen). 

Dry  pure  uric  acid  at  100°. 

a.  Determination  of  the  carbon  and  hydrogen  (§  183). 

b.  Determination  of  the  nitrogen, 
a.  After  § 185. 

0.  After  Dumas  (§  184). 


C5 

30 

35-71 

n2 

28 

h2 

2 

2-38 

03 

24 

28-58 

84 

100-00 

41.  Analysis  of  a Superphosphate  (§  235). 

42.  Analysis  of  Coal  (§  239). 

43.  Analysis  of  Ether. 

The  portion  employed  must  have  been  rendered  anhydrous  by  diges- 
tion with  fused  chloride  of  calcium  and  recently  rectified. 

Process  § 180. 


C8  

48 

64-87 

H10 

10 

13-51 

O, 

16 

21-62 

74 

100-00 

44.  Analysis  and  Determination  of  the  Equivalent  of 
Benzoic  Acid. 

a.  Determination  of  the  silver  in  benzoate  of  silver  as  directed  § 115, 
1 or  4. 

b.  Determination  by  any  suitable  method  of  the  carbon  and  hydrogen 
in  the  hydrated  acid  dried  at  100°.  Calculation,  § 200. 


EXERCISES  FOR  PRACTICE. 


579 


45.  Analysis  and  Determination  of  the  Equivalent  of  an  Organic 

Base. 

I 

Analysis  of  the  base  and  its  double  salt  with  platinum.  Calculation, 

§ 200. 

46.  Determination  of  the  Density  of  Camphor  Yapor. 
Method  described  § 191.  Calculation,  201. 


After  § 230. 


47.  Analysis  of  a Cast  Iron. 


APPENDIX 


ANALYTICAL  EXPERIMENTS.* 

1.  Action  op  Water  upon  Glass  and  Porcelain  Vessels,  in  the  Process 
op  Evaporation  (to  § 41). 

A large  bottle  was  filled  with  water  cautiously  distilled  from  a copper  boiler 
with  a tin  condensing  tube.  All  the  experiments  in  1 were  made  with  this 
water. 

a.  300  c.  o. , cautiously  evaporated  in  a platinum  dish,  left  a residue  weighing, 
after  ignition,  0 0005  grm.  =0*0017  per  1000. 

b.  600  c.  c.  were  evaporated,  boiling,  nearly  to  dryness,  in  a wide  flask  of  Bo- 
hemian glass;  the  residue  was  transferred  to  a platinum  dish,  and  the  flask 
rinsed  with  100  c.  c.  distilled  water,  which  was  added  to  the  residue  in  the 
dish ; the  fluid  in  the  latter  was  then  evaporated  to  dryness,  and  the  residue 


ignited. 

The  residue  weighed 0 0104  grm. 

Deducting  from  this  the  quantity  of  fixed  matter  originally  con- 
tained in  the  distilled  water,  viz 0*0012  “ 


There  remains  substance  taken  up  from  the  glass 0*0092  “ 

=0  0153  per  1000. 

In  three  other  experiments,  made  in  the  same  manner,  300  c.  c.  left,  in  two 
0 0049  grm.,  in  the  third  0*0037  grm.;  which,  calculated  for  600  c.  c.,  gives  an 

average  of 0*0090  grm. 

And  after  a deduction  of 0*0012  “ 


0*0078  “ 

=0*013  per  1000. 

We  may  therefore  assume  that  1 litre  of  water  dissolves,  when  boiled  down 
to  a small  bulk  in  glass  vessels,  about  14  milligrammes  of  the  constituents  of 
the  glass. 

c.  600  c.  c.  were  evaporated  nearly  to  dryness  in  a dish  of  Berlin  porcelain,  and 


in  all  other  respects  treated  as  in  b. 

The  residue  weighed 0*0015  grm. 

Deducting  from  this  the  quantity  of  fixed  matter  contained  in 

the  distilled  water,  viz 0*0012  “ 


There  remains  substance  taken  up  from  the  porcelain 0*0003  “ 

=0*0005  per  1000. 


2.  Action  of  Hydrochloric  Acid  upon  Glass  and  Porcelain  Vessels, 
in  the  Process  op  Evaporation  (to  § 41). 

The  distilled  water  used  in  1 was  mixed  with  yV  of  pure  hydrochloric  acid. 

a.  300  grm. , evaporated  in  a platinum  dish,  left  0 *002  grm.  residue. 

b.  300  grm. , evaporated  first  in  Bohemian  glass  nearly  to  dryness,  then  in  a 
platinum  dish,  left  0*0019  residue;  the  dilute  hydrochloric  acid,  therefore,  had 
not  attacked  the  glass. 

c.  300  grm.  evaporated  in  Berlin  porcelain,  &c. , left  0 *0036  grm. , accordingly 
after  deducting  0*002,  0*0016=0*0053  per  1000. 


* The  experiments  are  numbered  as  in  the  original  edition,  but  some  are  omitted. 


582 


EXPERIMENTS. 


d.  In  a second  experiment  made  in  the  same  manner  as  in  e. , the  residue 
amounted  to  0 0034,  accordingly  after  deducting  0 002,  0-0014=0  0047  per 
1000. 

Hydrochloric  acid,  therefore,  attacks  glass  much  less  than  water,  whilst 
porcelain  is  about  equally  affected  by  water  and  dilute  hydrochloric  acid.  This 
shows  that  the  action  of  water  upon  glass  consists  in  the  formation  of  soluble 
basic  silicates. 

3.  Action  of  Solution  of  Chloride  of  Ammonium  upon  Glass  and 
Porcelain  Vessels,  in  the  Process  of  Evaporation  (to  § 41)? 

In  the  distilled  water  of  1,  -jV  of  chloride  of  ammonium  was  dissolved,  and  the 
solution  filtered. 

a.  300  c.  c.  evaporated  in  a platinum  dish,  left  0 006  grm.  fixed  residue. 

b.  300  c.  c. , evaporated  first  nearly  to  dryness  in  Bohemian  glass,  then  to  dry- 
ness in  a platinum  dish,  left  0*0179  grm.;  deducting  from  this  0 006  grm.,  there 
remains  substance  taken  up  from  the  glass,  0 01 19=0 ‘0397  per  1000. 

c.  300  c.  c.,  treated  in  the  same  manner  in  Berlin  porcelain,  left  0*0178;  de- 
ducting from  this  0*006,  there  remains  0 '0118=0  0393  per  1000. 

Solution  of  chloride  of  ammonium,  therefore,  strongly  attacks  both  glass  and 
porcelain  in  the  process  of  evaporation. 

4.  Action  of  Solution  of  Carbonate  of  Soda  upon  Glass  and  Porce- 
lain Vessels  (to  § 41). 

In  the  distilled  water  of  1,  -fe  of  pure  crystallized  carbonate  of  soda  was 
dissolved. 

a.  300  c.  c.,  supersaturated  with  hydrochloric  acid  and  evaporated  to  dryness 
in  a platinum  dish,  &c.,  gave  0*0026  grm.  silicic  acid=0*0087  per  1000. 

b.  300  c.  c.  were  gently  boiled  for  three  hours  in  a glass  vessel,  the  evaporat- 
ing water  being  replaced  from  time  to  time  ; the  tolerably  concentrated 
liquid  was  then  treated  as  in  a;  it  left  a residue  weighing  0-1376  grm.  ; de- 
ducting from  this  the  0 ‘0026  grm.,  left  in  a,  there  remains  0*135  grm.  =0*450 
per  1000. 

c.  300  c.  c.,  treated  in  the  same  manner  as  in  5,  in  a por  elain  vessel,  left 
0*0099;  deducting  from  this  0*0026  grm.,  there  remains  0*0073=0*0243  per 
1000. 

Which  shows  that  boiling  solution  of  carbonate  of  soda  attacks  glass  very 
strongly,  and  porcelain  also  in  a very  marked  manner. 

5.  Water  Distilled  from  Glass  Vessels  (to  § 56,  1). 

42  *41  grm.  of  water  distilled  with  extreme  caution  from  a tall  flask  with  a 
Liebig’s  condenser,  left,  upon  evaporation  in  a platinum  dish,  a residue  weigh- 
ing, after  ignition,  0*0018  grm.,  consequently 

6.  Sulphate  of  Potash  and  Alcohol  (to  § 68,  a). 

a.  Ignited  pure  sulphate  of  potassa  was  digested  cold  with  absolute  alcohol, 
for  several  days,  with  frequent  shaking ; the  fluid  was  filtered  off,  the  filtrate  di- 
luted with  water,  and  then  mixed  with  chloride  of  barium.  It  remained  per- 
fectly clear  upon  the  addition  of  this  reagent,  but  after  the  lapse  of  a considera- 
ble time  it  began  to  exhibit  a slight  opalescence.  Upon  evaporation  to  dryness, 
there  remained  a very  trifling  residue,  which  gave,  however,  distinct  indications 
of  the  presence  of  sulphuric  acid. 

b.  The  same  salt  treated  in  the  same  manner,  with  addition  of  some  pure  con- 
centrated sulphuric  acid,  gave  a filtrate  which,  upon  evaporation  in  a platinum 
dish,  left  a clearly  perceptible  fixed  residue  of  sulphate  of  potassa. 

7.  Deportment  of  Chloride  of  Potassium  in  the  Air  and  at  a High 
Temperature  (to  § 68,  b). 

0*9727  grm.  of  ignited  (not  fused)  pure  chloride  of  potassium,  heated  for  10 
minutes  to  dull  redness  in  an  open  platinum  dish,  lost  0*0007  grm.  ; the  salt  was 
then  kept  for  10  minutes  longer  at  the  same  temperature,  when  no  further  dimi- 
nution of  weight  was  observed.  Heated  to  bright  redness  and  semi-fusion,  the 


EXPERIMENTS. 


583 


salt  suffered  a further  loss  of  weight  to  the  extent  of  0*0009  grm.  Ignited  in- 
tensely and  to  perfect  fusion,  it  lost  0 *0034  grm. , more. 

Eighteen  hours’  exposure  to  the  air  produced  not  the  slightest  increase  of 
weight. 

8.  Solubility  op  Potassio-Bichloride  op  Platinum  in  Alcohol  (to 

§ 68,  e). 

a.  In  absence  of  free  Hydrochloric  Acid. 

a.  An  excess  of  perfectly  pure,  recently  precipitated  potassio-bichloride  of  pla- 
tinum was  digested  for  6 days  at  15 — 20%  with  alcohol  of  97*5  per  cent.,  in  a stop- 
pered bottle,  with  frequent  shaking.  72*5  grm.  of  the  perfectly  colorless  filtrate 
left  upon  evaporation  in  a platinum  dish,  a residue  which,  dried  at  100’,  weighed 
0*006  grm.  ; 1 part  of  the  salt  requires  therefore  12083  parts  of  alcohol  of  97*5 
per  cent,  for  solution. 

/?.  The  same  experiment  was  made  with  spirit  of  wine  of  76  per  cent.  The 
filtrate  might  be  said  to  be  colorless ; upon  evaporation,  slight  blackening  ensued, 
on  which  account  the  residue  was  determined  as  platinum.  75  *5  grm.  yielded 
0 008  grm.  platinum,  corresponding  to  0*02  grm.  of  the  salt.  One  part  of  the 
salt  dissolves  accordingly  in  3775  parts  of  spirit  of  wine  of  76  per  cent. 

y.  The  same  experiment  was  made  with  spirit  of  wine  of  55  per  cent.  The 
filtrate  was  distinctly  yellowish.  63*2  grm.  left  0 0241  grm.  platinum,  cor- 
responding to  0 *06  grm.  of  the  salt.  One  part  of  the  salt  dissolves  accordingly 
in  1053  parts  of  spirit  of  wine  of  55  per  cent. 

b.  In  •presence  of  free  Hydrochloric  Acid. 

Recently  precipitated  potassio-bichloride  of  platinum  was  digested  cold  with 
spirit  of  wine  of  76  per  cent. , to  which  some  hydrochloric  acid  had  been  added. 
The  solution  was  yellowish;  67  grm.  left  0*0146  grm.  platinum,  which  corre- 
sponds to  0*0365  grm.  of  the  salt.  One  part  of  the  salt  dissolves  accordingly  in 
1835  parts  of  spirit  of  wine,  mixed  with  hydrochloric  acid. 

9.  Sulphate  of  Soda  and  Alcohol  (to  § 69,  a). 

Experiments  'made  with  pure  anhydrous  sulphate  of  soda,  in  the  manner  de- 
scribed in  6,  showed  that  this  salt  comports  itself  both  with  pure  alcohol,  and 
with  alcohol  containing  sulphuric  acid,  exactly  like  the  sulphate  of  potassa. 

10.  Deportment  of  ignited  Sulphate  of  Soda  in  the  Air  (to  § 69,  a). 

2*5169  grm.  anhydrous  sulphate  of  soda  were  exposed,  in  a watch-glass,  to  the 
open  air  on  a hot  summer  day.  The  first  few  minutes  passed  without  any  in- 
crease of  weight,  but  after  the  lapse  of  5 hours  there  was  an  increase  of  0 *0061 
grm. 

12.  Deportment  of  Chloride  of  Sodium  in  the  Air  (to  § 69,  b). 

4*3281  grm.  of  chemically  pure,  moderately  ignited  (not  fused)  chloride  of 
sodium,  which  had  been  cooled  under  a bell-glass  over  sulphuric  acid,  acquired 
during  45  minutes’  exposure  to  the  (somewhat  moist)  air,  an  increase  of  weight 
of  0*0009  grm. 

13.  Deportment  of  Chloride  of  Sodium  upon  Ignition  by  itself  and 
with  Chloride  of  Ammonium  (to  § 69,  &). 

4*3281  grm.  chemically  pure,  ignited  chloride  of  sodium  were  dissolved  in 
water,  in  a moderate-sized  platinum  dish,  and  pure  chloride  of  ammonium  was 
added  to  the  solution,  which  was  then  evaporated  and  the  residue  gently  heated 
until  the  evolution  of  chloride  of  ammonium  fumes  had  apparently  ceased.  The 
residue  weighed  4*3334  grm.  It  was  then  very  gently  ignited  for  about  2 min- 
utes, and  after  this  re-weighed,  when  the  weight  was  found  to  be  4*3314  grm. 
A few  minutes’  ignition  at  a red  heat  reduced  the  weight  to  4*3275  grm.,  and  2 
minutes’  further  ignition  at  a bright  red  heat  (upon  which  occasion  white  fumes 
were  seen  to  escape),  to  4*3249  grm. 

14.  Deportment  of  Carbonate  of  Soda  in  the  Air  and  on  Ignition  (to 
§ 69,  c). 

2*1061  grm.  of  moderately  ignited  chemically  pure  carbonate  of  soda  were  ex- 


584 


EXPERIMENTS. 


posed  to  the  air  in  an  open  platinum  dish  in  July  in  bad  weather ; after  10  min- 
utes the  weight  was  2T078,  after  1 hour  2*1118,  after  5 hours  2*1257. 

1 *4212  grm.  of  moderately  ignited  chemically  pure  carbonate  of  soda  were  ig- 
nited for  5 minutes  in  a covered  platinum  crucible  ; no  fusion  took  place,  and  the 
weight  was  unaltered.  Heated  more  strongly  for  5 minutes,  it  partially  fused, 
and  then  weighed  1 *4202.  After  being  kept  fusing  for  5 minutes,  it  weighed 
1*4135. 

15.  Deportment  of  Chloride  of  Ammonium  upon  Evaporation  and 
Drying  (to  § 70,  a). 

0*5625  grm.  pure  and  perfectly  dry  chloride  of  ammonium  was  dissolved  in 
water  in  a platinum  dish,  evaporated  to  dryness  in  the  water-bath  and  completely 
dried  ; the  weight  was  now  found  to  be  0 5622  grm.  (ratio  100  : 99  94).  It  was 
again  heated  for  15  minutes  in  the  water-bath,  and  afterwards  re-weighed,  when 
the  weight  was  found  to  be  0*5612  grm.  (ratio  100  : 99*77).  Exposed  once  more 
for  15  minutes  to  the  same  temperature,  the  residue  weighed  0*5608  grm.  (ratio 
100:99*69). 

16.  Solubility  of  Ammonio-Bichloride  of  Platinum  in  Alcohol 
(to  § 70,  b). 

a.  In  absence  of  free  Hydrochloric  Acid. 

a.  An  excess  of  perfectly  pure,  recently  precipitated  ammonio -bichloride  of 
platinum  was  digested  for  6 days,  at  15 — 20°,  with  alcohol  of  97*5  per  cent.,  in  a 
stoppered  bottle,  with  frequent  agitation. 

74  *3  grm.  of  the  perfectly  colorless  filtrate  left,  upon  evaporation  and  ignition 
in  a platinum  dish,  0*0012  grm.  platinum,  corresponding  to  0*0028  of  the  salt. 
One  part  of  the  salt  requires  accordingly  26535  parts  of  alcohol  of  97  *5  per  cent. 

0.  The  same  experiment  was  made  with  spirit  of  wine  of  76  per  cent.  The 
filtrate  was  distinctly  yellowish. 

81*75  grm.  left  0*0257  platinum,  which  corresponds  to  0*0584  grm.  of  the  salt. 
One  part  of  the  salt  dissolves  accordingly  in  1406  parts  of  spirit  of  wine  of  76  per 
cent. 

y.  The  same  experiment  was  made  with  spirit  of  wine  of  55  per  cent.  The 
filtrate  was  distinctly  yellow.  Slight  blackening  ensued  upon  evaporation,  and 
56*5  grm.  left  0*0364  platinum,  which  corresponds  to  0*08272  grm.  of  the  salt. 
Consequently,  1 part  of  the  salt  dissolves  in  665  parts  of  spirit  of  wine  of  55  per 
cent. 

b.  In  presence  of  Hydrochloric  Acid. 

The  experiment  described  in  /?  was  repeated,  with  this  modification,  that  some 
hydrochloric  acid  was  added  to  the  spirit  of  wine.  76*5  grm.  left  0 0501  grm. 
of  platinum,  which  corresponds  to  0*1139  grm.  of  the  salt.  672  parts  of  the 
acidified  spirit  had  therefore  dissolved  1 part  of  the  salt. 

I 

17.  Solubility  of  Carbonate  of  Baryta  in  Water  (to  § 71,  b). 

a.  In  Cold  Water. — Perfectly  pure,  recently  precipitated  Ba  O,  C 02  was  di- 

gested for  5 days  with  water  of  16 — 20°,  with  frequent  shaking.  The  mixture 
was  filtered,  and  a portion  of  the  filtrate  tested  with  sulphuric  acid,  another  por- 
tion with  ammonia  ; the  former  reagent  immediately  produced  turbidity  in  the 
fluid,  the  latter  only  after  the  lapse  of  a considerable  time.  84*82  grm.  of  the 
solution  left,  upon  evaporation,  0*0060  Ba  O,  C 02.  1 part  of  that  salt  dissolves 

consequently  in  14137  parts  of  cold  water. 

b.  In  Hot  Water. — The  same  carbonate  of  baryta  being  boiled  for  10  minutes 
with  pure  distilled  water,  gave  a filtrate  manifesting  the  same  reactions  as  that 
prepared  with  cold  water,  and  remaining  perfectly  clear  upon  cooling.  84*82 
grm.  of  the  hot  solution  left,  upon  evaporation,  0 0055  grm.  of  carbonate  of  ba- 
ryta. One  part  of  that  salt  dissolves  therefore  in  15421  parts  of  boiling  water. 

18.  Solubility  of  Carbonate  of  Baryta  in  Water  containing  Ammonia 
and  Carbonate  of  Ammonia  (to  § 71,  b). 

A solution  of  chemically  pure  chloride  of  barium  was  mixed  with  ammonia  and 
carbonate  of  ammonia  in  excess,  gently  heated  and  allowed  to  stand  at  rest  for  12 
hours ; the  fluid  was  then  filtered  off ; the  filtrate  remained  perfectly  clear  upon 


EXPERIMENTS. 


585 


addition  of  sulphuric  acid  ; but  after  the  lapse  of  a very  considerable  time,  a 
hardly  perceptible  precipitate  separated.  84 '82  grin,  of  the  filtrate  left,  upon 
evaporation  in  a small  platinum  dish,  and  subsequent  gentle  ignition,  0 0006  grm. 
1 part  of  the  salt  had  consequently  dissolved  in  141000  parts  of  the  fluid. 

19.  Solubility  of  Silico-Fluoride  of  Barium  in  Water  (to  § 71,  c). 

a.  Recently  precipitated,  thoroughly  washed  silico-fluoride  of  barium  was  di- 
gested for  4 days  in  cold  water,  with  frequent  shaking ; the  fluid  was  then  filtered 
off,  and  a portion  of  the  filtrate  tested  with  dilute  sulphuric  acid,  another  portion 
with  solution  of  sulphate  of  lime  ; both  reagents  produced  turbidity — the  former 
immediately,  the  latter  after  one  or  two  seconds — precipitates  separated  from 
both  portions  after  the  lapse  of  some  time.  84 ’82  grm.  of  the  filtrate  left  a resi- 
due which,  after  being  thoroughly  dried,  weighed  0 0223  grm.  1 part  of  the  salt 
had  consequently  required  3802  parts  of  cold  water  for  its  solution. 

b.  A portion  of  another  sample  of  recently  precipitated  silico-fluoride  of  barium 
was  heated  with  water  to  boiling,  and  the  solution  allowed  to  cool  (upon  which  a 
portion  of  the  dissolved  salt  separated).  The  cold  fluid  was  left  for  a consider- 
able time  longer  in  contact  with  the  undissolved  salt,  and  was  then  filtered  off. 
The  filtrate  showed  the  same  deportment  with  solution  of  sulphate  of  lime  as 
that  of  a.  84 ’82  grm.  of  it  left  0*025  grm.  One  part  of  the  salt  had  accordingly 
dissolved  in  3392  parts  of  water. 

20.  Solubility  of  Silico-Fluoride  of  Barium  in  Water  acidified 
with  Hydrochloric  Acid  (to  § 71,  c). 

a.  Recently  precipitated  pure  silico-fluoride  of  barium  was  digested  with  fre- 
quent agitation  for  3 weeks  with  cold  water  acidified  with  hydrochloric  acid. 
The  filtrate  gave  with  sulphuric  acid  a rather  copious  precipitate.  84  '82  grm . 
left  0*1155  grm.  of  thoroughly  dried  residue,  which,  calculated  as  silico-fluoride 
of  barium,  gives  733  parts  of  fluid  to  1 part  of  that  salt. 

b.  Recently  precipitated  pure  silico-fluoride  of  barium  was  mixed  with  water 
very  slightly  acidified  with  hydrochloric  acid,  and  the  mixture  heated  to  boiling. 
Cooled  to  12°,  84*82  grm.  of  the  filtrate  left  a residue  of  01322  grm.,  which  gives 
040  parts  of  fluid  to  1 part  of  the  salt. 

N.  B.  The  solution  of  silico-fluoride  of  barium  in  hydrochloric  acid  is  not  effect- 
ed without  decomposition  ; at  least,  the  residue  contained,  even  after  ignition, 
a rather  large  proportion  of  chloride  of  barium. 

21.  Solubility  of  Sulphate  of  Strontia  in  Water  (to  § 72,  a). 

a.  In  Water  of  14°. 

84*82  ^rm.  of  a solution  prepared  by  4 days’  digestion  of  recently  precipitated 
sulphate  of  strontia  with  water  at  the  common  temperature,  left  0 0123  grm.  of 
sulphate  of  strontia.  One  part  of  Sr  O,  S 03  dissolves  consequently  in  6895 
parts  of*  water. 

b.  In  Water  of  100°. 

84*82  grm.  of  a solution  prepared  by  boiling  recently  precipitated  sulphate  of 
strontia  several  hours  with  water,  left  0 *0088  grm.  Consequently  1 part  of  Sr  O, 
S 03  dissolves  in  9638  parts  of  boiling  water. 

22.  Solubility  of  Sulphate  of  Strontia  in  Water  containing^  Hydro- 
chloric Acid  and  Sulphuric  Acid  (to  § 72,  a). 

a.  84*82  grm.  of  a solution  prepared  by  3 days’  digestion,  left  0*0077  grm. 
Sr  O,  S03. 

b.  42*41  grm.  of  a solution  prepared  by  4 days’  digestion,  left  0*0036  grm. 

c.  Pure  carbonate  of  strontia  was  dissolved  in  an  excess  of  hydrochloric  acid, 
and  the  solution  precipitated  with  an  excess  of  sulphuric  acid  and  then  allowed 
to  stand  in  the  cold  for  a fortnight.  84*82  grm.  of  the  filtrate  left  0*0066  grm. 

In  a.  1 part  of  Sr  0,  S 03  required  11016  part3. 

b.  1 “ “ 11780'  “ 

c.  1 “ “ 12791  “* 


Mean 


11862  parts. 


586 


EXPERIMENTS. 


23.  Solubility  of  Sulphate  of  Strontia  in  dilute  Nitric  Acid, 
Hydrochloric  Acid,  and  Acetic  Acid  (to  § 72,  a). 

a.  Recently  precipitated  pure  sulphate  of  strontia  was  digested  for  2 days  in 
the  cold  with  nitric  acid  of  4*8  per  cent  150  grin,  of  the  filtrate  left  0*3451  grin. 
1 part  of  the  salt  required  accordingly  435  parts  of  the  dilute  acid  for  its  solution  ; 
in  another  experiment  1 part  of  the  salt  was  found  to  require  429  parts  of  the 
dilute  acid.  Mean,  432  parts. 

b.  The  same  salt  was  digested  for  2 days  in  the  cold  with  hydrochloric  acid  of 
8*5  per  cent.  100  grm.  left  0 2115.  and  in  another  experiment,  0*2104  grm.  1 
part  of  the  salt  requires,  accordingly,  in  the  mean,  474  parts  of  hydrochloric 
acid  of  8 5 per  cent,  for  its  solution. 

c.  The  same  salt  was  digested  for  2 days  in  the  cold  with  acetic  acid  of  15 '6 
percent.  A,  HO.  100  grm.  left  0 0126,  and  in  another  experiment,  0 0129  grm. 
1 part  of  the  salt  requires,  accordingly,  in  the  mean,  7843  parts  of  acetic  acid  of 
15*6  per  cent. 

24.  Solubility  of  Carbonate  of  Strontia  in  Cold  Water  (to  § 72,  b). 

Recently  precipitated,  thoroughly  washed  Sr  O,  C 02  was  digested  several 
days  with  cold  distilled  water,  with  frequent  shaking.  84*82  grm.  of  the  filtrate 
left,  upon  evaporation,  a residue  weighing,  after  ignition,  0*0047  grm.  1 
part  of  carbonate  of  strontia  requires  therefore  18045  parts  of  water  for  its 
solution. 

25.  Solubility  of  Carbonate  of  Strontia  in  Water  containing 
Ammonia  and  Carbonate  of  Ammonia  (to  § 72,  b). 

Recently  precipitated,  thoroughly  washed  carbonate  of  strontia  was  digested 
for  four  weeks  with  cold  water  containing  ammonia  and  carbonate  of  ammonia, 
with  frequent  shaking.  84*82  grm.  of  the  filtrate  left  0*0015  grm.  Sr  O,  C 02. 
Consequently,  1 part  of  the  salt  requires  56545  parts  of  this  fluid  for  its  solution. 

If  solution  of  chloride  of  strontium  is  precipitated  with  carbonate  of  ammonia 
and  ammonia  as  directed  § 102,  2,  a,  sulphuric  acid  produces  no  turbidity  in  the 
filtrate,  after  addition  of  alcohol. 

26.  Solubility  of  Carbonate  of  Lime  in  Cold  and  in  Boiling  Water 
(to  § 73,  b). 

a.  A solution  prepared  by  boiling  as  in  26,  b,  was  digested  in  the  cold  for  4 

weeks,  with  frequent  agitation,  with  the  undissolved  precipitate.  84*82  grm. 
left  0*0080  Ca  O,  C 02.  1 part  therefore  required  10601  parts. 

b.  Recently  precipitated  Ca  O,  C 02  was  boiled  for  some  time  with  distilled 

water.  42*41  grm.  of  the  filtrate  left,  upon  evaporation  and  gentle  ignition  of 
the  residue,  0*0048  Ca  O,  C 02.  1 part  requires  consequently  8834  parts  of 

boiling  water. 

27.  Solubility  of  Ca  O.  C 02  in  Water  containing  Ammonia  and  Carbo- 
nate of  Ammonia  (to  § 73,  b). 

Pure  dilute  solution  of  chloride  of  calcium  was  precipitated  with  carbonate  of 
ammonia  and  ammonia,  allowed  to  stand  24  hours,  and  then  filtered.  84*82  grm. 
j eft  0*0013  grm.  Ca  O,  C 02.  1 part  requires  consequently  65246  parts. 

28.  Deportment  of  Carbonate  of  Lime  upon  Ignition  in  a Platinum 
Crucible  (to  § 73,  b). 

0*7955  grm.  of  perfectly  dry  carbonate  of  lime  was  exposed,  in  a small  and 
thin  platinum  crucible,  to  the  gradually  increased,  and  finally  most  intense  heat 
of  a good  Berzelius’  lamp.  The  crucible  was  open  and  placed  obliquely.  After 
the  first  15  minutes  the  mass  weighed  0*6482 — after  half  an  hour  0*6256 — after  one 
hour  0*5927,  which  latter  weight  remained  unaltered  after  15  minutes’  additional 
heating.  This  corresponds  to  74*5  per  cent.,  whilst  the  proportion  of  lime  in 
the  carbonate  is  calculated  at  56  per  cent.  ; there  remained  therefore  evidently 
still  a considerable  amount  of  the  carbonic  acid. 

29.  Composition  of  Oxalate  of  Lime  dried  at  100°  (to  § 73,  c). 

0*8510  grm.  of  thoroughly  dry  pure  carbonate  of  lime  was  dissolved  in  hydro- 
chloric acid  ; the  solution  was  precipitated  with  oxalate  of  ammonia  and  am- 


EXPERIMENTS. 


587 


monia,  and  the  precipitate  collected  upon  a weighed  filter  and  dried  at  100°, 
until  the  weight  remained  constant.  The  oxalate  of  lime  so  produced  weighed 
12461  grm.  Calculating  this  as  Ca  0,  C2  03+aq.,  the  amount  found  contained 
0*4772  Ca  0,  which  corresponds  to  56  07  per  cent,  in  the  carbonate  of  lime  ; the 
calculated  proportion  of  lime  in  the  latter  is  56  per  cent. 

30.  Deportment  of  Sulphate  of  Magnesia  in  the  Air  and  upon  Igni- 
tion (to  § 74,  a). 

0 8135  grm.  of  perfectly  pure  anhydrous  Mg  O,  S 03  in  a covered  platinum  cru- 
cible acquired,  on  a fine  and  warm  day  in  June,  in  half  an  hour,  an  increase  of 
weight  of  0*004  grm.,  and  in  the  course  of  12  hours,  of  0 067  grm.  The  salt 
could  not  be  accurately  weighed  in  the  open  crucible,  owing  to  continual  increase 
of  weight. 

0*8135  grm.,  exposed  for  some  time  to  a very  moderate  red  heat,  suffered  no 
diminution  of  weight ; but  after  5 minutes’  exposure  to  an  intense  red  heat,  the 
substance  was  found  to  have  lost  0 ‘0075  grm. , and  the  residue  gave  no  longer  a 
clear  solution  with  water.  About  0 2 grm.  of  pure  sulphate  of  magnesia  ex- 
posed in  a small  platinum  crucible,  for  15  to  20  minutes,  to  the  heat  of  a powerful 
blast  gaslamp,  gave,  with  dilute  hydrochloric  acid,  a solution  in  which  chloride 
of  barium  failed  to  produce  the  least  turbidity. 

31.  Solubility  of  the  Basic  Phosphate  of  Magnesia  and  Ammonia  in 
pure  Water  (to  § 74,  b ). 

a.  Recently  precipitated  basic  phosphate  of  magnesia  and  ammonia  was 
thoroughly  washed  with  water,  then  digested  for  24  hours  with  water  of  about 


15°,  with  frequent  shaking. 

84 ‘42  grm.  of  the  filtrate  left 0'0047  grm. 

of  pyrophosphate  of  magnesia. 

b.  The  same  precipitate  was  digested  in  the  same  manner  for  72 
hours 

84  42  grm.  of  the  filtrate  left 0 0043  “ 


Mean  0 0045 


which  corresponds  to  0 00552  grm.  of  the  anhydrous  double  salt.  1 part  of  that 
salt  dissolves  therefore  in  15293  parts  of  pure  water. 

The  cold  saturated  solution  gave,  with  ammonia,  after  the  lapse  of  a short 
time,  a distinctly  perceptible  crystalline  precipitate; — on  the  addition  of  phos- 
phate of  soda,  it  remained  perfectly  clear,  and  even  after  the  lapse  of  two  days 
no  precipitate  had  formed ; — phosphate  of  soda  and  ammonia  produced  a precipi- 
tate as  large  as  that  by  ammonia. 

32.  Solubility  of  Basic  Phosphate  of  Magnesia  and  Ammonia  in  Water 
CONTAINING  AMMONIA  (to  § 74,  b). 

a.  Pure  basic  phosphate  of  magnesia  and  ammonia  was  dissolved  in  the  least 
possible  amount  of  nitric  acid ; a large  quantity  of  water  was  added  to  the  solu- 
tion, then  ammonia  in  excess.  The  mixture  was  allowed  to  stand  at  rest  for  24 
hours,  then  filtered;  its  temperature  was  14°.  84 ‘42  grm.  left  0'0015  pyrophos- 

phate of  magnesia,  which  corresponds  to  0 00184  of  the  anhydrous  double  salt. 
Consequently  1 part  of  the  latter  requires  45880  parts  of  ammoniated  water  for 
its  solution. 

b Pure  basic  phosphate  of  magnesia  and  ammonia  was  digested  for  4 weeks 
with  ammoniated  water,  with  frequent  shaking;  the  fluid  (temperature  14°)  was 
then  filtered  off;  126*63  grm.  left  0 0024  pyrophosphate  of  magnesia,  which  cor- 
responds to  0 *00296  of  the  double  salt.  1 part  of  it  therefore  dissolves  in  42780 
parts  of  ammoniated  water.  Taking  the  mean  of  a and  5,  1 part  of  the  double 
salt  requires  44330  parts  of  ammoniated  water  for  its  solution. 

33.  Another  Experiment  on  the  same  Subject  (to  § 74,  b). 

Recently  precipitated  phosphate  of  magnesia  and  ammonia,  most  carefully 
washed  with  water  containing  ammonia,  was  dissolved  in  water  acidified  with 
hydrochloric  acid,  ammonia  added  in  excess,  and  allowed  to  stand  in  the  cold  for 
24  hours.  169*64  grm.  of  the  filtrate  left  0*0031  pyrophosphate  of  magnesia, 
corresponding  to  0*0038  of  anhydrous  phosphate  of  magnesia  and  ammonia.  1 
part  of  the  double  salt  required  therefore  44600  parts  of  the  fluid. 


588 


EXPERIMENTS. 


34.  Solubility  of  the  Basic  Phosphate  of  Magnesia  and  Ammonia  in 
Water  containing  Chloride  of  Ammonium  (to  § 74,  b). 

Recently  precipitated,  thoroughly  washed  basic  phosphate  of  magnesia  and 
ammonia  was  digested  in  the  cold  with  a solution  of  1 part  of  chloride  of  ammo- 
nium in  5 parts  of  water.  18 ‘4945  grm.  of  the  filtrate  left  0 002  pyrophosphate 
of  magnesia,  which  corresponds  to  0 *00245  of  the  double  salt.  1 part  of  the  salt 
dissolves  therefore  in  7548  parts  of  the  fluid. 

35.  Solubility  of  the  Basic  Phosphate  of  Magnesia  and  Ammonia  in 
Water  containing  Ammonia  and  Chloride  of  Ammonium  (to  § 74,  b). 

Recently  precipitated,  thoroughly  washed  phosphate  of  magnesia  and  ammo- 
nia was  digested  in  the  cold  with  a solution  of  1 part  of  chloride  of  ammonium 
in  7 parts  of  ammoniated  water.  23 ‘1283  grm.  of  the  filtrate  left  0 0012  pyro- 
phosphate of  magnesia,  which  corresponds  to  0 00148  of  the  double  salt.  1 part 
of  the  double  salt  requires  consequently  15627  parts  of  the  fluid  for  its  solution. 

36.  Deportment  of  Acid  Solutions  of  Pyrophosphate  of  Magnesia 
with  Ammonia  (to  § 74,  c ). 

0 *3985  grm.  pyrophosphate  of  magnesia  was  treated  for  several  hours,  at  a high 
temperature,  with  concentrated  sulphuric  acid.  This  exercised  no  perceptible 
action.  It  was  only  after  the  addition  of  some  water  that  the  salt  dissolved. 
The  fluid,  heated  for  some  time,  gave,  upon  addition  of  ammonia  in  excess,  a 
crystalline  precipitate,  which  was  filtered  off  after  18  hours ; the  quantity  of 
pyrophosphate  of  magnesia  obtained  was  0 *3805  grm. , that  is,  95  *48  per  cent. 
Phosphate  of  soda  produced  in  the  filtrate  a trifling  precipitate,  which  gave 
O'OISO  grm.  of  pyrophosphate  of  magnesia,  that  is,  3*76  per  cent. 

0 3565  grm.  pyrophosphate  of  magnesia  was  dissolved  in  3 grm.  nitric  acid, 
of  1 ‘2  sp.  gr. ; the  solution  was  heated,  diluted,  and  precipitated  with  ammo- 
nia : the  quantity  of  pyrophosphate  of  magnesia  obtained  amounted  to  0 3485 
grm. , that  is,  98  '42  per  cent. ; 0 '4975  grm.  was  treated  in  the  same  manner  with 
7 '6  grm.  of  the  same  nitric  acid  : the  quantity  re-obtained  was  0'4935  grm.,  that 
is,  99 '19  per  cent. 

0 786  grm.  treated  in  the  same  manner  with  16  2 grm.  of  nitric  acid,  gave 
0'7765  grm.,  that  is,  98 '79  per  cent. 

The  result  of  these  experiments  may  be  tabulated  thus : — 

Proportion  of  2 Mg  O,  P Oo 


to  nitric  acid. 

Re-obtained. 

Loss. 

1 

: 9 

98 '42  per  cent. 

1*58 

1 

: 15 

99*19  “ 

0'81 

1 

: 20 

98'79  “ 

1*21 

37.  Solubility  of  pure  Magnesia  in  Water  (to  § 74,  d). 
a.  In  Gold  Water. 


Perfectly  pure  well-crystallized  sulphate  of  magnesia  was  dissolved  in  water, 
and  the  solution  precipitated  with  carbonate  of  ammonia  and  caustic  ammonia ; 
the  precipitate  was  thoroughly  washed — in  spite  of  which  it  still  retained  a per- 
ceptible trace  of  sulphuric  acid — then  dissolved  in  pure  nitric  acid,  an  excess  of 
acid  being  carefully  avoided.  The  solution  was  then  re -precipitated  with  car- 
bonate of  ammonia  and  caustic  ammonia,  and  the  precipitate  thoroughly  washed. 
The  so-prepared  perfectly  pure  basic  carbonate  of  magnesia  was  ignited  in  a 
platinum  crucible  until  the  weight  remained  constant.  The  residuary  pure  mag- 
nesia was  then  digested  in  the  cold  for  24  hours  with  distilled  water,  with  fre- 
quent shaking.  The  distilled  water  used  was  perfectly  free  from  chlorine,  and 
left  no  fixed  residue  upon  evaporation. 

a.  84  82  grm.  of  the  filtrate,  cautiously  evaporated  in  a platinum  dish,  left  a 
residue  weighing,  after  ignition,  0 0015  grm.  1 part  of  the  pure  magnesia  dis- 
solved therefore  in 56546 

parts  of  cold  water. 

The  digestion  was  continued  for  48  hours  longer,  when 

0.  84 '82  grm.  left  0 0016  grm.  1 part  required  therefore 53012 

y.  84 '82  grm.  left  0'0015  grm.  1 part  required 56546 


Average  55368 


EXPERIMENTS. 


589 


The  solution  of  magnesia  prepared  in  the  cold  way  has  a feeble  yet  distinct 
alkaline  reaction,  which  is  most  easily  perceived  upon  the  addition  of  very  faintly 
reddened  tincture  of  litmus ; the  alkaline  reaction  of  the  solution  is  perfectly 
manifest  also  with  slightly  reddened  litmus  paper,  or  with  turmeric  or  dahlia 
paper,  if  these  test-papers  are  left  for  some  time  in  contact  with  the  solution. 

Alkaline  carbonates  fail  to  render  the  solution  turbid,  even  upon  boiling. 

Phosphate  of  soda  also  fails  to  impair  the  clearness  of  the  solution,  but  if  the 
fluid  is  mixed  with  a little  ammonia  and  shaken,  it  speedily  becomes  turbid,  and 
deposits  after  some  time  a perceptible  precipitate  of  basic  phosphate  of  magnesia 
and  ammonia. 

I 

b.  In  Hot  Water. 

Upon  boiling  pure  magnesia  with  water,  a solution  is  obtained  which  comports 
itself  in  every  respect  like  the  cold-prepared  solution  of  magnesia.  A hot-pre- 
pared solution  of  magnesia  does  not  become  turbid  upon  cooling,  nor  does  a cold- 
prepared  solution  upon  boiling.  84 ‘82  grin,  of  hot-prepared  solution  of  magnesia 
left  0 0016  grm.  Mg  O. 

38.  Solubility  op  Pure  Magnesia  in  Solutions  op  Chloride  op 
Potassium  and  Chloride  op  Sodium  (to  § 74,  d). 

3 flasks  of  equal  size  were  charged  as  follows: — 

1.  With  1 grm.  pure  chloride  of  potassium,  200  c.  c.  water  and  some  perfectly 
pure  magnesia. 

2.  With  1 grm.  pure  chloride  of  sodium,  200  c.  c.  water  and  some  pure  mag- 
nesia. 

3.  With  200  c.  c.  water  and  some  pure  magnesia. 

The  contents  of  the  3 flasks  were  kept  boiling  for  40  minutes,  then  filtered, 
and  the  clear  filtrates  mixed  with  equal  quantities  of  a mixture  of  phosphate  of 
soda,  chloride  of  ammonium  and  ammonia.  After  12  hours  a very  slight  preci- 
pitation was  visible  in  3,  and  a considerably  larger  precipitation  had  taken  place 
in  1 and  2. 

39.  Precipitation  op  Alumina  by  Ammonia,  etc.  (to  § 75,  a). 

a.  Ammonia  produces  in  neutral  solutions  of  salts  of  alumina  or  of  alum,  as  is 
well  known,  a gelatinous  precipitate  of  hydrate  of  alumina.  Upon  further  ad- 
dition of  ammonia  in  considerable  excess,  the  precipitate  redissolves  gradually, 
but  not  completely. 

b.  If  a drop  of  a dilute  solution  of  alum  is  added  to  a copious  amount  of 
ammonia,  and  the  mixture  shaken,  the  solution  appears  almost  perfectly 
clear  ; however,  after  standing  at  rest  for  some  time,  slight  flakes  separate. 

c.  If  a solution  of  alumina,  mixed  with  a large  amount  of  ammonia,  is  filtered,  and 

а.  The  filtrate  boiled  for  a considerable  time,  flakes  of  hydrate  of  alumina 
separate  gradually  in  proportion  as  the  excess  of  ammonia  escapes. 

/?.  The  filtrate  mixed  with  solution  of  chloride  of  ammonium,  a very  percep- 
tible flocculent  precipitate  of  hydrate  of  alumina  separates  immediately  ; the 
whole  of  the  hydrated  alumina  present  in  the  solution  will  thus  separate  if  the 
chloride  of  ammonium  be  added  in  sufficient  quantity. 

y.  The  filtrate  mixed  with  sesquicarbonate  of  ammonia,  the  same  reaction 
takes  place  as  in  0. 

б.  The  filtrate  mixed  with  solution  of  chloride  of  sodium  or  chloride  of 
potassium,  no  precipitate  separates,  but,  after  several  days’  standing,  slight 
flakes  of  hydrate  of  alumina  subside,  owing  to  the  loss  of  ammonia  by  evaporation. 

d.  If  a neutral  solution  of  alumina  is  precipitated  with  carbonate  of  ammonia, 
or  if  a solution  strongly  acidified  with  hydrochloric  or  nitric  acid  is  precipitated 
with  pure  ammonia,  or  if  to  a neutral  solution  a sufficient  amount  of  chloride 
of  ammonium  is  added  besides  the  ammonia ; even  a considerable  excess  of  the 
precipitants  will  fail  to  redissolve  the  precipitated  alumina,  as  appears  from  the 
continued  perfect  clearness  of  the  filtrates  upon  protracted  boiling  and  evapora- 
tion. 

40.  Precipitation  op  Alumina  by  Sulphide  op  Ammonium  (to  § 75,  a). 

(. Experiments  made  by  Mr.  J.  Fuchs,  formerly  Assistant  in  my  Laboratory .) 

a.  50  c.  c.  of  a solution  of  pure  ammonia-alum,  which  contained  0 3939 


590 


EXPERIMENTS. 


alumina,  were  mixed  with  50  c.  c.  water  and  10  c.  c.  solution  of  sulphide  of 
ammonium,  and  filtered  after  ten  minutes.  The  ignited  precipitate  weighed 
0 3825  grm. 

b.  The  same  experiment  was  repeated  with  100  c.  c.  water ; the  precipitate 
weighed  0-3759  grm. 

c.  The  same  experiment  was  repeated  with  200  c.  c.  water ; the  precipitate 
weighed  0*3642  grm. 

41.  Precipitation  of  Sesquioxide  of  Chromium  by  Ammonia  (to  § 
76,  a). 

Solutions  of  sesquichloride  of  chromium  and  of  chrome-alum  (concentrated 
and  dilute,  neutral  and  acidified  with  hydrochloric  acid)  were  mixed  with  am- 
monia in  excess.  All  the  filtrates  drawn  off  immediately  after  precipitation  ap- 
peared red,  but  when  filtered  after  ebullition,  they  all  appeared  colorless,  if  the 
ebullition  had  been  sufficiently  protracted. 

42.  Solubility  of  the  Basic  Carbonate  of  Zinc  in  Water  (to  § 77,  a). 

Perfectly  pure,  recently  (hot)  precipitated  basic  carbonate  of  zinc  was  gently 
heated  with  distilled  water,  and  subsequently  digested  cold  for  many  weeks, 
with  frequent  shaking.  The  clear  solution  gave  no  precipitate  with  sulphide  of 
ammonium,  not  even  after  long  standing. 

84  '82  grm.  left  0‘0014  grm.  oxide  of  zinc,  which  corresponds  to  0'0019 
basic  carbonate  of  zinc  (74  per  cent,  of  Zn  O being  assumed  in  this  salt). 
One  part  of  the  basic  carbonate  requires  therefore  44642  parts  of  water  for  so- 
lution. 

In  each  of  the  three  following  numbers  the  sulphide  was  pre- 
cipitated  from  the  solution  of  the  neutral  salt  with  addition  of  chloride  of  ammo- 
nium by  yellow  sulphide  of  ammonium,  and  allowed  to  stand  in  a closed  vessel. 
After  24  hours  the  clear  fluid  was  poured  on  to  6 filters  of  equal  size,  and  the 
precipitate  was  then  equally  distributed  among  them.  The  washing  was  at 
once  commenced  and  continued,  without  interruption,  the  following  fluids  being 
used  : — 

I.  Pure  water. 

II.  Water  containing  sulphuretted  hydrogen. 

III.  Water  containing  sulphide  of  ammonium. 

IV.  Water  containing  chloride  of  ammonium,  afterwards  pure  water. 

V.  Water  containing  sulphuretted  hydrogen  and  chloride  of  ammonium, 
afterwards  water  containing  sulphuretted  hydrogen. 

VI.  Water  containing  sulphide  of  ammonium  and  chloride  of  ammonium, 
afterwards  water  containing  sulphide  of  ammonium. 

43.  Deportment  of  Sulphide  of  Zinc  on  Washing  (to  § 77,  c ). 

The  filtrates  were  at  first  colorless  and  clear.  On  washing,  the  first  three  fil- 
trates ran  through  turbid,  the  turbidity  was  strongest  in  II.  and  weakest  in 
III.  ; the  last  three  remained  quite  clear.  On  adding  sulphide  of  ammonium  no 
change  took  place  ; the  turbidity  of  the  first  three  was  not  increased,  the  clear- 
ness of  the  last  three  was  not  impaired.  Chloride  of  ammonium  therefore  de- 
cidedly exercises  a favorable  action,  and  the  water  containing  it  may  be  displaced 
by  water  containing  sulphide  of  ammonium. 

44.  Deportment  of  Sulphide  of  Manganese  on  Washing  (to  § 78,  e). 

The  filtrates  were  at  first  clear  and  colorless.  But  after  the  washing  had 
been  continued  some  time,  I.  appeared  colorless,  slightly  opalescent ; II. 
whitish  and  turbid ; III.  yellowish  and  turbid  ; IV.  colorless,  slightly  turbid ; 
V.  slightly  yellowish,  nearly  clear  ; VI.  clear,  yellowish.  To  obtain  a filtrate 
that  remains  clear,  therefore,  the  wash-water  must  at  first  contain  chloride  of 
ammonium.  Addition  of  sulphide  of  ammonium  also  cannot  be  dispensed 
with,  as  all  the  filtrates  obtained  without  this  addition  gave  distinct  pre- 
cipitates of  sulphide  of  manganese  when  the  reagent  was  subsequently  added  to 
them. 


EXPERIMENTS. 


591 


45.  Deportment  of  Sulphide  of  Nickel  f also  of  Sulphide  of  Cobalt 
and  Sulphide  of  Iron)  on  Washing  (to  § 79,  d). 

In  the  experiments  with  sulphide  of  nickel  the  clear  filtrates  were  put  aside, 
and  then  the  washing  was  proceeded  with.  The  washings  of  the  first  3 ran 
through  turbid,  of  the  last  3 clear.  When  the  washing  was  finished,  I.  was 
colorless  and  clear ; II.  blackish  and  clear  ; III.  dirty  yellow  and  clear  ; IVi  col- 
orless and  clear ; V.  slightly  opalescent ; VI.  slightly  brownish  and  opalescent. 
On  addition  of  sulphide  of  ammonium,  I.  became  brown  ; II.  remained  unalter- 
ed ; III.  remained  unaltered ; IV.  became  black  and  opaque  ; V.  became  brown 
and  clear  ; VI.  became  pure  yellow  and  clear. 

Sulphide  of  cobalt  and  sulphide  of  iron  behaved  in  an  exactly  similar  manner. 
It  is  plain  that  these  sulphides  oxidize  more  rapidly  when  the  wash -water 
contains  chloride  of  ammonium,  unless  sulphide  of  ammonium  is  also  present. 
Hence  it  is  necessary  to  wash  with  a fluid  containing  sulphide  of  ammo- 
nium ; and  the  addition  of  chloride  of  ammonium  at  first  is  much  to  be  re- 
commended, as  this  diminishes  the  likelihood  of  our  obtaining  a muddy  fil- 
trate. 

46.  Deportment  of  Hydrate  of  Protoxide  of  Cobalt  precipitated 
by  Alkalies  (to  § 80,  a). 

A solution  of  protochloride  of  cobalt  was  precipitated  boiling  with  solution 
of  soda,  and  the  precipitate  washed  with  boiling  water  until  the  filtrate  gave  no 
longer  the  least  indication  of  presence  of  chlorine.  The  dried  and  ignited  resi- 
due, heated  with  water,  manifested  no  alkaline  reaction.  It  was  reduced  by  ig- 
nition in  hydrogen  gas,  and  the  metallic  cobalt  digested  hot  with  water.  The 
decanted  water  manifested  no  alkaline  reaction,  even  after  considerable  con- 
centration ; but  the  metallic  cobalt,  brought  into  contact,  moist,  with  turmeric 
paper,  imparted  to  the  latter  a strong  brown  color. 

47.  Solubility  of  Carbonate  of  Lead  (to  § 83,  a). 

a.  In  pure  Water. 

Recently  precipitated  and  thoroughly  washed  pure  carbonate  of  lead  was 
digested  for  8 days  with  water  at  the  common  temperature,  with  frequent 
shaking.  84 ’42  grm.  of  the  filtrate  were  evaporated,  with  addition  of  some 
pure  sulphuric  acid;  the  residuary  sulphate  of  lead  weighed  0‘0019  grm., 
which  corresponds  to  0 '001 67  carbonate  of  lead.  One  part  of  the  latter  salt 
dissolves  therefore  in  50551  parts  of  water.  The  solution,  mixed  with  sul- 
phuretted hydrogen  water,  remained  perfectly  colorless,  not  the  least  tint 
being  detected  in  it,  even  upon  looking  through  it  from  the  top  of  the  test- 
cylinder. 

b.  In  Water  containing  a little  Acetate  of  Ammonia  and  also  Carbonate  of 
Ammonia  and  Ammonia. 

A highly  dilute  solution  of  pure  acetate  of  lead  was  mixed  with  carbonate  of 
ammonia  and  ammonia  in  excess,  and  the  mixture  gently  heated  and  then  al- 
lowed to  stand  at  rest  for  several  days.  84  '42  grm.  of  the  filtrate  left,  upon  evap- 
oration with  a little  sulphuric  acid,  0 0041  grm.  sulphate  of  lead,  which  corre- 
sponds to  0 0036  of  the  carbonate.  One  part  of  the  latter  salt  requires  accordingly 
23450  parts  of  the  above  fluid  for  solution.  The  solution  was  mixed  with  sulphu- 
retted hydrogen  water ; when  looking  through  the  fluid  from  the  top  of  the  test- 
cylinder,  a distinct  coloration  was  visible  ; but  when  looking  through  the  cylinder 
laterally,  this  coloration  was  hardly  perceptible.  Traces  of  sulphide  of  lead 
separated  after  the  lapse  of  some  time. 

c.  In  Water  containing  a large  proportion  of  Nitrate  of  Ammonia , together  with 
Carbonate  of  Ammonia  and  Caustic  Ammonia. 

A highly  dilute  solution  of  acetate  of  lead  was  mixed  with  nitric  acid,  then 
with  carbonate  of  ammonia  and  ammonia  in  excess  ; the  mixture  was  gently 
heated,  and  allowed  to  stand  at  rest  for  8 days.  The  filtrate,  mixed  with  sul- 
phuretted hydrogen,  exhibited  a very  distinct  brownish  color  upon  looking  through 
it  from  the  top  of  the  cylinder  ; but  this  color  appeared  very  slight  only  when 
looking  through  the  cylinder  laterally.  The  amount  of  lead  dissolved  was  unques- 
tionably more  considerable  than  in  b. 


592 


EXPERIMENTS. 


48.  Solubility  of  Oxalate  of  Lead  (to  § 83,  b). 

A dilute  solution  of  acetate  of  lead  was  precipitated  with  oxalate  of  ammonia 
and  ammonia,  the  mixture  allowed  to  stand  at  rest  for  some  time,  and  then  fil- 
tered. The  filtrate,  mixed  with  sulphuretted  hydrogen,  comported  itself  exactly 
like  the  filtrate  of  No.  47,  b.  The  same  deportment  was  observed  in  another 
similar  experiment,  in  which  nitrate  of  ammonia  had  been  added  to  the  solution. 

49.  Solubility  of  Sulphate  of  Lead  in  Pure  Water  (to  § 83,  d). 

Thoroughly  washed  and  still  moist  sulphate  of  lead  was  digested  for  5 days 
with  water,  at  10—15°,  with  frequent  shaking.  84  42  grm.  of  the  filtrate  (filtered 
off  at  11°)  left  0 0037  grm.  sulphate  of  lead.  Consequently  1 part  of  this  salt 
requires  22816  parts  of  pure  water  of  11°  for  solution. 

The  solution,  mixed  with  sulphuretted  hydrogen,  exhibited  a distinct  brown 
color  when  viewed  from  the  top  of  the  cylinder,  but  this  color  appeared  very 
slight  upon  looking  through  the  cylinder  laterally. 

50.  Solubility  of  Sulphate  of  Lead  in  Water  containing  Sulphuric 
Acid  (to  § 83,  d). 

A highly  dilute  solution  of  acetate  of  lead  was  mixed  with  an  excess  of  dilute 
pure  sulphuric  acid ; the  mixture  was  very  gently  heated,  and  the  precipitate 
allowed  several  days  to  subside.  80 '31  grm  of  the  filtrate  left  0 0022  grm. 

sulphate  of  lead.  One  part  of  this  salt  dissolves  therefore  in  36504  parts  of  water 
containing  sulphuric  acid.  The  solution,  mixed  with  sulphuretted  hydrogen, 
appeared  colorless  to  the  eye  looking  through  the  cylinder  laterally,  and  very 
little  darker  when  viewed  from  the  top  of  the  cylinder. 

51.  Solubility  of  Sulphate  of  Lead  in  Water  containing  Ammoniacal 
Salts  and  free  Sulphuric  Acid  (to  § 83,  d). 

A highly  dilute  solution  of  acetate  of  lead  was  mixed  with  a tolerably  large 
amount  of  nitrate  of  ammonia,  and  sulphuric  acid  in  excess  added.  After  sev- 
eral days’  standing,  the  mixture  was  filtered.  The  filtrate  was  nearly  indifferent 
to  sulphuretted  hydrogen  water  ; viewed  from  the  top  of  the  cylinder,  it  looked 
hardly  perceptibly  darker  than  pure  water. 

52.  Deportment  of  Sulphate  of  Lead  upon  Ignition  (to  § 83,  d). 

Speaking  of  the  determination  of  the  atomic  weight  of  sulphur,  Erdmann  and 
Marchand*  state  that  sulphate  of  lead  loses  some  sulphuric  acid  upon  ignition. 
In  order  to  inform  myself  of  the  extent  of  this  loss,  and  to  ascertain  how  far  it 
might  impair  the  accuracy  of  the  method  of  determining  lead  as  a sulphate,  I 
heated  2 '2151  grm.  of  absolutely  pure  Pb  O,  S 03  to  the  most  intense  redness, 
over  a spirit-lamp  with  double  draught.  I could  not  perceive  the  slightest  de- 
crease of  weight ; at  all  events,  the  loss  did  not  amount  to  0 '0001  grm. 

53.  Deportment  of  Sulphide  of  Lead  on  Drying  at  100°  (to  § 83,  e). 

Sulphide  of  lead  was  precipitated  from  a solution  of  pure  acetate  of  lead  with 
sulphuretted  hydrogen,  and  when  dry,  kept  for  a considerable  time  at  100°  and 
weighed  occasionally.  The  following  numbers  represent  the  results  of  the  sev- 
eral weighings : — 

I.  0-8154.  II.  0-8164.  III.  0*8313.  IY.  0 8460.  Y.  0 864. 

54.  Deportment  of  Metallic  Mercury  at  the  Common  Temperature 
and  upon  Ebullition  with  Water  (to  § 84,  a). 

To  ascertain  in  what  manner  loss  of  metallic  mercury  occurs  upon  drying,  and 
likewise  upon  boiling  with  water,  and  to  determine  which  is  the  best  method  of 
drying,  I made  the  following  experiments : — 

I treated  6 4418  grm.  of  perfectly  pure  mercury  in  a watch-glass,  with  dis- 
tilled water,  removed  the  water  again  as  far  as  practicable  (by  decantation  and  fin- 
ally by  means  of  blotting-paper),  and  weighed.  I now  had  6 4412  grm.  After  sev- 
eral hours’  exposure  to  the  air,  the  mercury  was  reduced  to  6*4411.  I placed  these 
6 *4411  grm.  under  a bell-jar  over  sulphuric  acid,  the  temperature  being  about  17°. 


* Journ.  fur.  Prakt.  Cliem.  31,  385. 


EXPERIMENTS. 


593 


After  the  lapse  of  24  hours  the  "weight  had  not  altered  in  the  least.  I introduced 
the  6 '441 1 grm.  mercury  into  a flask,  treated  it  with  a copious  quantity  of  dis- 
tilled water,  and  boiled  for  15  minutes  violently.  I then  placed  the  mercury 
again  upon  the  watch-glass,  dried  it  most  carefully  with  blotting-paper,  and 
weighed.  The  weight  was  now  6 '4402  grm.  Finding  that  a trace  of  mercury 
had  adhered  to  the  paper,  I repeated  the  same  experiment  with  the  6 4402  grm. 
After  15  minutes’  boiling  with  water,  the  mercury  had  again  lost  0 0004  grm. 
The  remaining  6 '4398  grm.  were  exposed  to  the  air  for  6 days  (in  summer,  during 
very  hot  weather),  after  which  they  were  found  to  have  lost  only  0 0005  grm. 

55.  Deportment  of  Sulphide  of  Mercury  with  Solution  of  Potassa, 
Sulphide  of  Ammonium,  etc.  (to  § 84,  c). 

a.  If  recently  precipitated  pure  sulphide  of  mercury  is  boiled  with  pure  solu- 
tion of  potassa,  not  a trace  of  it  dissolves  in  that  fluid ; hydrochloric  acid  pro- 
duces no  precipitate,  nor  even  the  least  coloration,  in  the  filtrate. 

b.  If  sulphide  of  mercury  is  boiled  with  solution  of  potassa,  with  addition  of 
some  sulphuretted  hydrogen  water,  sulphide  of  ammonium,  or  sulphur,  complete 
solution  is  effected, 

c.  If  freshly  precipitated  sulphide  of  mercury  is  digested  in  the  cold  with 
yellowish  or  very  yellow  sulphide  of  ammonium,  slight,  but  distinctly  percepti- 
ble traces  are  dissolved,  while  in  the  case  of  hot  digestion,  scarcely  any  traces 
of  mercury  can  be  detected  in  the  solution.  * 

d.  Thoroughly  washed  sulphide  of  mercury,  moistened  with  water,  suffers  no 
alteration  upon  exposure  to  the  air;  at  least,  the  fluid  which  I obtained  by 
washing  sulphide  of  mercury  which  had  been  thus  exposed  for  24  hours,  did  not 
manifest  acid  reaction,  nor  did  it  contain  mercury  or  sulphuric  acid. 

56.  Deportment  of  Oxide  of  Copper  upon  Ignition  (to  § 85,  b). 

Pure  oxide  of  copper  (prepared  from  nitrate  of  copper)  was  ignited  in  a plat- 
inum crucible,  then  cooled  under  a bell-jar  over  sulphuric  acid,  and  finally 
weighed.  The  weight  was  3 '542  grm.  The  oxide  was  then  most  intensely 
ignited  for  5 minutes,  over  a Berzelius’  lamp,  and  weighed  as  before,  when  the 
weight  was  found  unaltered  ; the  oxide  was  then  once  more  ignited  for  5 minutes, 
but  with  the  same  result. 

57.  Deportment  of  Oxide  of  Copper  in  the  air  (to  § 85,  b). 

A platinum  crucible  containing  4 '3921  grm.  of  gently  ignited  oxide  of  copper 
(prepared  from  the  nitrate)  stood  for  10  minutes,  covered  with  the  lid,  in  a warm 
room  ( in  winter) ; the  weight  of  the  oxide  of  copper  was  found  to  have  increased 
to  4 '3939  grm. 

The  oxide  of  copper  was  then  intensely  ignited  over  a spirit-lamp ; after  10 
minutes’  standing  in  the  covered  crucible,  the  weight  had  not  perceptibly  in- 
creased ; after  24  hours  it  had  increased  by  0 '0036  grm. 

58.  Deportment  of  Sulphide  of  Bismuth  upon  drying  at  100°  (to 

§ 86,  e). 

0'4558  grm.  of  sulphide  of  bismuth  prepared  in  the  wet  way  were  placed  in 
the  desiccator  on  a watch  glass  and  allowed  to  stand  at  the  common  tempera- 
ture. After  3 hours  the  weight  was  0'4270,  after  6 hours  0‘4258,  after  2 days 
the  same. 

0'3602  grm.  of  the  sulphide  of  bismuth  so  dried  was  put  into  a water-bath,  in 
15  minutes  it  weighed  0'3596,  half  an  hour  afterwards  0'3599,  in  half  an  hour 
more  0'3603,  in  two  hours  0 3626.  In  a second  experiment  the  drying  was  kept 
up  for  4 days,  and  a continual  increase  of  weight  was  observed. 

0'5081  grm.  of  sulphide  of  bismuth  dried  in  the  desiccator  was  heated  in  a 
boat  in  a stream  of  carbonic  acid.  After  gentle  ignition  the  weight  was  0 5002, 
after  repeated  heating  0'4992.  The  sulphide  of  bismuth  was  visibly  volatilized 
on  ignition  in  the  current  of  carbonic  acid. 


* Comp,  my  experiments  in  the  Zeitachrift  f.  Anal.  Chem.  3,  140. 

38 


594 


EXPERIMENTS. 


59.  Deportment  op  Sulphide  of  Cadmium  with  Ammonia,  etc  (to 
§ 87,  c). 

Recently  precipitated  pure  sulphide  of  cadmium  was  diffused  through  water, 
and  the  following  experiments  were  made  with  the  mixture. 

a.  A portion  was  digested  cold  with  ammonia  in  excess,  and  filtered.  The  fil- 
trate remained  perfectly  clear  upon  addition  of  hydrochloric  acid. 

b.  Another  portion  was  digested  hot  with  excess  of  ammonia,  and  filtered. 
This  filtrate  likewise  remained  perfectly  clear  upon  addition  of  hydrochloric 
acid. 

c.  Another  portion  was  digested  for  some  time  with  solution  of  cyanide  of  po- 
tassium, and  filtered.  This  filtrate  also  remained  perfectly  clear  upon  addition 
of  hydrochloric  acid. 

d.  Another  portion  was  digested  with  hydrosulphate  of  sulphide  of  ammonium, 
and  filtered.  The  turbidity  which  hydrochloric  acid  imparted  to  this  filtrate  was 
pure  white. 

(A  remark  made  by  Wackenroder,  in  Buchner’s  Repertor.  d.  Pharm., 
xlvi.  226,  induced  me  to  make  these  experiments.) 

60.  Deportment  of  Precipitated  Tersulphide  of  Antimony  on  dry- 
ing (to  § 90,  a). 

0 ’2899  grm.  of  pure  precipitated  tersulphide  of  antimony  dried  in  the  desicca- 
tor lost,  when  dried  at  1 00  , 0 0007. 

0"4457  grm.  of  the  substance  dried  at  100°  lost,  when  heated  to  blackening  in 
a stream  of  carbonic  acid,  0 0011  water.  it 

0 1982  grm.  of  the  substance  dried  at  100°  gave  up  0 0012,  when  heated  to 
blackening  in  a stream  of  carbonic  acid,  and  after  stronger  heating,  during  which 
fumes  of  sulphide  of  antimony  began  to  escape,  the  total  loss  amounted  to 
0 0022  grm. 

0 1670  grm.  of  the  substance  dried  at  100°  lost  0*0005  grm.  on  being  heated  to 
blackening  in  a stream  of  carbonic  acid. 

61.  Amount  of  Water  in  Hydrated  Silicic  Acid  (to  § 93,  9). 

(. Experiments  made  by  my  assistant , Mr.  Lippert.) 

A dilute  solution  of  soluble  glass  was  slowly  dropped  into  hydrochloric  acid, 
as  long  as  the  precipitate  continued  to  dissolve  rapidly,  then  the  clear  fluid  was 
heated  in  the  water-bath,  till  it  set  to  a transparent  jelly.  This  jelly  was  dried 
as  far  as  possible  with  blotting  paper,  diffused  in  water,  and  washed  by  decanta- 
tion till  the  fluid  altogether  ceased  to  give  the  chlorine  reaction.  It  was  then 
transferred  to  a filter,  and  the  latter  spread  on  blotting  paper  and  exposed  till  a 
crumbly  mass  was  left  from  the  spontaneous  evaporation  of  water.  One  half 
(I.)  was  dried  for  8 weeks  in  the  desiccator  over  sulphuric  acid,  with  occasional 
trituration,  the  other  half  (II. ) was  dried  under  similar  circumstances,  but  in  a 
vacuum.  Both  were  transferred  to  closed  tubes  and  these  were  kept  in  the  de- 
siccator. 

The  weighing  of  the  substance  dried  at  100°  was  effected  between  watch 
glasses.  For  the  purpose  of  igniting  the  residue,  it  was  allowed  to  satiate  itself 
with  aqueous  vapor  by  exposure  to  the  air,  otherwise  a considerable  quantity  of 
the  substance  would  have  been  lost,  then  water  was  dropped  upon  it  in  the  watch 
glass,  then  it  was  rinsed  into  a platinum  crucible,  dried  in  a water-bath,  and 
ignited,  at  first  cautiously,  towards  the  end,  intensely. 

The  substance  I.  contained 

Water,  escaping  at  or  below  100° 

“ “ above  100° 

Silicic  acid 


100-00  100-00 


Expt.  1. 
419 
4 76 
91-05 


Expt.  2. 

9-28 

90*72 


Consequently  the  hydrate  dried  at  100°  consists  of  4*97  water  and  95  03  silicio 
acid.  In  the  substance  dried  in  the  desiccator  the  oxygen  of  the  total  water  : 
the  oxygen  of  the  silicic  acid,  according  to  the  first  experiment : : 1 : 6*1,  ac- 


EXPERIMENTS. 


595 


cording  to  the  second  experiment  : : 1 : 5 '86.  And  in  the  substance  dried  at 
100°  the  oxygen  of  the  water  : the  oxygen  of  the  silicic  acid  : : 1 : 11  *5. 


The  substance  II.  contained 

Water,  escaping  at  or  below  100° 

“ “ above  100° 

Silicic  acid 


Expt.  1. 

Expt.  2. 

Expt.  3. 

4 75 
5*26 

4*71 

5*21 

J-  9*95 

89*99 

90*08 

90*05 

100*00 

100  00 

100*00 

Consequently  the  hydrate  dried  at  100°  consists  on  the  average  of  5 ’49  water 
and  94 ‘51  silicic  acid.  In  the  substance  dried  in  a vacuum  over  sulphuric  acid 
the  oxygen  of  the  total  water  : the  oxygen  of  the  silicic  acid— on  an  aver- 
age : : 1 : 5 41.  And  in  the  substance  dried  at  100°  the  oxygen  of  the  water  : 
the  oxygen  of  the  silicic  acid  : : 1 : 10 ‘43. 

62.  Determination  of  Baryta  by  Precipitation  with  Carbonate  of 
Ammonia  (to  § 101,  2,  a). 

0 7553  grm.  pure  ignited  chloride  of  barium  precipitated  after  § 101,  2,  a , gave 
0*7142  Ba  O,  C 02,  which  corresponds  to  0-554719  Ba  O = 73  44  per  cent.  (100 
parts  of  Ba  Cl  ought  to  have  given  73-59  parts).  The  result  accordingly  was 
99 '79  instead  of  100. 

63.  Determination  of  Baryta  in  Organic  Salts  (to  § 101,  2,  b). 

0’686  grm.  racemate  of  baryta  (2  BaO,  C8H4O10-f-5  aq.)  treated  according  to 
§ 101,  2,  5,  gave  0 408  carbonate  of  baryta  = 0*3169  Ba  O = 46  20  per  cent,  (cal- 
culated 46-38  per  cent.) ; i. e. , 99*61  instead  of  100. 

64.  Determination  of  Strontia  as  Sulphate  of  Strontia  (to  § 102, 

1,«). 

a An  aqueous  solution  of  1*2398  grm.  Sr  Cl  was  precipitated  with  sulphuric 
acid  in  excess,  and  the  precipitated  sulphate  of  strontia  washed  with  water.  It 
weighed  1-4113,  which  corresponds  to  0 "795408  Sr  O = 64*15  per  cent,  (calculated 
65*38  per  cent.) ; i. e. , 9812  instead  of  100. 

b.  1*1510  grm.  Sr  O,  C 02  was  dissolved  in  excess  of  hydrochloric  acid,  the 
solution  diluted,  and  then  precipitated  with  sulphuric  acid  ; the  precipitated  Sr 
O,  S 03  was  washed  with  water ; it  weighed  1*4024  = 0*79039  Sr  O = 68*68  per 
cent,  (calculated  70*07  per  cent.) ; i. e. , 98  02  instead  of  100. 

65.  Determination  of  Strontia  as  Sulphate,  with  Correction  (to 

§ 102,  1,  a). 

The  filtrate  obtained  in  No.  64,  5,  weighed  190*84  grm.  According  to  experi- 
ment No.  22,  11862  parts  of  water  containing  sulphuric  acid  dissolve  1 part  of 
sulphate  of  strontia;  therefore,  190*84  grm.  dissolve  0*0161.  The  washings 
weighed  63  61  grm.  According  to  experiment  No.  21,  6895  parts  of  water 
dissolve  1 part  of  Sr  O,  S 03  ; therefore,  63*61  grm.  dissolve  0*0092  grm. 

Adding  0*0161  and  0*0092  to  the  1 *4024  actually  obtained,  we  find  the  total 
amount  = 1 *4277  grm.,  which  corresponds  to  0*80465  Sr  O = 69*91  per  cent,  in  Sr 

0,  C 02  (calculated  70*07  per  cent.) ; i.e.,  99*77  instead  of  100. 

66.  Determination  of  Strontia  as  Carbonate  of  Strontia  (to  § 102,  2). 

1*3104  grm.  chloride  of  strontium,  precipitated  according  to  § 102,  2,  gave 
1*2204  Sr  O,  C 02,  containing  0*8551831  Sr  0=65*26  per  cent,  (calculated  65*38) ; 

1. e.,  99*82  instead  of  100. 

In  the  four  following  experiments,  and  also  in  No.  72,  pure  air- 
dried  carbonate  of  lime  was  used,  in  a portion  of  which  the  amount  of  anhydrous 
carbonate  had  been  determined  by  very  cautious  heating.  0*7647  grm.  left 
0*7581  grm.,  which  weight  remained  unaltered  upon  further  (extremely  gentle) 
ignition;  the  air-dried  carbonate  contained  accordingly  55*516  per  cent,  of  lime. 


596 


EXPERIMENTS. 


67.  Determination  op  Lime  as  Sulphate  of  Lime  by  Precipitation 
(to  § 103,  1,  a). 

1 '186  grm.  of  “the  air-dried  carbonate  of  lime  ” was  dissolved  in  hydrochloric 
acid,  and  the  solution  precipitated  with  sulphuric  acid  and  alcohol,  after  § 103, 
1,  a.  Obtained  1*5949  grm.  Ca  O,  S 03,  containing  0*65598  Ca  O,  i.e.t  55*31  per 
cent,  (calculated  55*51),  which  gives  99*64  instead  of  100. 

68.  Determination  of  Ca  O as  Ca  0,  C 02,  by  Precipitation  with 
Carbonate  of  Ammonia  and  washing  with  Pure  Water  (to  § 103,  2,  a). 

A hydrochloric  acid  solution  of  1*1437  grm.  of  “the  air-dried  carbonate  of 
lime  ” gave  upon  precipitation  as  directed,  1 *1243  grm.  anhydrous  carbonate  of 
lime,  corresponding  to  0*629608  Ca  O = 55*05  per  cent,  (calculated 55 *51  per  cent.) 
which  gives  99*17  instead  of  100. 

69.  Determination  of  Ca  O as  Ca  O,  C 02,  by  Precipitation  with 
Oxalate  of  Ammonia  from  Alkaline  Solution  (to  § 103,  2,  ft,  a). 

1*1734  grm.  of  “the  air-dried  carbonate  of  lime”  dissolved  in  hydrochloric 
acid,  and  treated  as  directed  § 103,  2,  ft,  «,  gave  1 *1632  grm.  Ca  0,  C 02  (reaction 
not  alkaline),  containing  0*651392  of  Ca  O = 55*513  per  cent,  (calculated  55  *516 
per  cent.),  which  gives  99*99  instead  of  100. 

70.  Determination  of  Lime  as  Oxalate  (to  § 103,  2,  ft,  a). 

0*857  grm.  of  “ the  air-dried  carbonate  of  lime  ” were  dissolved  in  hydrochloric 
acid ; the  solution  was  precipitated  with  oxalate  of  ammonia  and  ammonia,  the 
precipitate  washed,  and  then  dried  at  100°,  until  the  weight  remained  constant. 
The  precipitate  (2  Ca  O,  O + 2 aq.)  weighed  1*2461  grm.,  containing  0*477879 
Ca  O = 55*76  per  cent,  (calculated  55*516  per  cent.),  which  gives  100*45  instead 
of  100. 

71.  Volumetric  Determination  of  Lime  Precipitated  as  Oxalate  (to 
§ 103,  2,  ft,  a). 

Six  portions,  of  10  c.  c.  each,  were  taken  of  a solution  of  pure  chloride  of  cal- 
cium ; in  2 portions  the  lime  was  determined  in  the  gravimetric  way  (by  pre- 
cipitation with  oxalate  of  ammonia,  and  weighing  as  Ca  O,  C 02) ; in  two  by  the 
alkalimetric  method  (p.  171,  «),  and  in  two  by  precipitation  with  oxalate  of  am- 
monia, and  estimation  of  the  oxalic  acid  in  the  precipitate  by  solution  of  per- 
manganate of  potassa.  The  following  were  the  results  obtained: — 


a.  In  the  gravimetric 


way. 

0*5617  Ca  O,  C 02 
0*5620  “ 


ft.  By  the  alkalimetric 
method. 

0*5614 

0*5620 


c.  By  solution  of  per- 
manganate of  potassa. 


0*5613 

0*5620 


72.  Determination  of  Ca  O as  Ca  O,  C 02  by  Precipitation  as  2 Ca  O,  O 
from  Acid  Solution  (to  § 103,  2,  ft,  /?)„ 


0*857  grm.  of  “ the  air-dried  carbonate  of  lime  ” dissolved  in  hydrochloric  acid 
and  precipitated  from  this  solution  according  to  the  directions  of  § 103,  2,  ft,  /?, 
gave  0*8476  carbonate  of  lime  (which  did  not  manifest  alkaline  reaction,  and  the 
weight  of  which  did  not  vary  in  the  least  upon  evaporation  with  carbonate  of 
ammonia),  containing  0*474656  Ca  O = 55  *39  per  cent,  (calculated  55*51),  which 
gives  99*78  instead  of  100. 


73.  Determination  of  Magnesia  as  2 Mg  O,  P 05  (to  § 104,  2). 

a.  A solution  of  1 *0587  grm.  pure  anhydrous  sulphate  of  magnesia  in  water, 
precipitated  according  to  § 104,  2,  gave  0*9834  pyrophosphate  of  magnesia,  con- 
taining 0*35438  magnesia  = 33*476  per  cent,  (calculated  33*33  per  cent.),  which 
gives  100*43  instead  of  100. 

ft.  0*9672  Mg  O,  S 03  gave  0 *8974  2 Mg  O,  P 05  = 33*43  per  cent,  of  Mg  0 (cal- 
culated 33*33),  which  gives  100*30  instead  of  100. 


EXPERIMENTS. 


597 


74.  Precipitation  of  Acetate  of  Zinc  by  Sulphuretted  Hydrogen 
(to  § 108,  b). 

a.  A solution  of  pure  acetate  of  zinc  was  treated  with  the  gas  in  excess,  al- 
lowed to  stand  at  rest  for  some  time,  and  then  filtered.  The  filtrate  was  mixed 
with  ammonia  ; it  remained  perfectly  clear  at  first,  and  even  after  long  standing 
a few  hardly  visible  'flakes  only  had  separated. 

b.  A solution  of  acetate  of  zinc  to  which  a tolerably  large  amount  of  acetic 
acid  had  been  added  previously  to  the  precipitation  with  sulphuretted  hydrogen, 
showed  exactly  the  same  deportment. 

75.  Determination  of  Iron  as  Sulphide  (to  § 118,  2). 

10  c.  c.  of  a pure  solution  of  sesquichloride  of  iron  was  precipitated  with  am- 
monia; obtained  04453  Fe2  03  =0  10171  Fe. 

10  c.  c.  was  precipitated  with  ammonia  and  sulphide  of  Ammonium,  and  treated 
after  § 118,  2,  obtained  01596  Fe  S = 010157  Fe. 

10  c.  c.  again  yielded  01605  Fe  S = 0.1021  Fe. 

76.  Determination  of  Lead  as  Chromate  (to  § 116,  4). 

1*0083  grm.  pure  nitrate  of  lead  were  treated  according  to  § 116,  4.  The  pre- 
cipitate was  collected  on  a weighed  filter,  and  dried  at  100%  obtained  0*9871 
grm.  =0  *67833  Pb  O.  This  gives  67  *3  per  cent.  Calculation  67 ’4. 

0‘9814  nitrate  of  lead  again  yielded  0'9625  chromate  = 67  *4  per  cent. 

77.  Determination  of  Mercury  in  the  Metallic  State,  in  the  Wet 
Way,  by  Means  of  Protochloride  of  Tin  (to  § 118,  1,  b). 

2* 01  grm.  chloride  of  mercury  gave  1465  grm.  metallic  mercury =72 '88  per 
cert,  (calculated  73 ’83  per  cent.),  which  gives  98 ‘71  instead  of  100  (Schaffner). 
The  loss  is  not  inherent  in  the  method,  i.e.,  it  does  not  arise  from  mercury 
evaporating  during  the  ebullition  and  desiccation  (Expt.  No.  54) ; but  its  origin 
lies  in  the  fact  that  one  usually  does  not  allow  sufficient  time  for  the  mercury  to 
settle  quite  completely,  and  in  general  is  not  careful  enough  in  decanting,  and 
drying  with  paper,  &c. 

78.  Determination  of  Copper  by  Precipitation  with  Zing  in  a Plat- 
inum Disii  (to  § 119,  2). 

30 '882  grm.  pure  sulphate  of  copper  were  dissolved  in  water  to  250  c.  c. ; 10 

c.  c.  of  the  solution  contained  accordingly  0 '31387  grm.  metallic  copper. 

a.  10  c.  c.  precipitated  with  zinc  in  a platinum  dish,  gave  0*3140=100*06  per 
cent. 

b.  In  a second  experiment  10  c.  c.  gave  0'3138  = 100  per  cent. 

79.  Behavior  of  Copper  Precipitated  by  Zinc  on  Ignition  in  Hydro- 
gen (to  p.  229,  foot-note). 

A dilute  solution  of  sulphate  of  copper  was  acidified  with  hydrochloric  acid 
and  precipitated  with  zinc  in  a platinum  crucible,  the  precipitate  was  washed 
with  water,  then  with  alcohol,  and  dried  at  100\  0'7961  grm.  of  this  was  ig- 

nited for  i of  an  hour  in  a stream  of  hydrogen.  It  then  weighed  0 '7952  grm. 

80.  Determination  of  Copper  as  Subsulphocyanide  (to  § 119,  3,  b). 

0 '5965  grm.  of  pure  sulphate  of  copper  was  dissolved  in  a little  water,  and, 
after  addition  of  an  excess  of  sulphurous  acid,  precipitated  with  sulphocyanide 
of  potassium.  The  well-washed  precipitate,  dried  at  100%  weighed  0*2893,  cor- 
responding to  04892  Cu  0=31*72  per  cent.  As  sulphate  of  copper  contains  31*83 
per  cent.,  this  gives  99*66  instead  of  100. 

81.  Determination  of  Copper  by  De  Haen’s  Method  (to  § 119,  4,  a). 

Four  10  c.  c.’s  of  a solution  of  sulphate  of  copper,  each  10  c.  c.  containing 
0*0254  grm.  Cu,  were  severally  mixed  with  iodide  of  potassium,  then  with  50  c.  c. 
of  a solution  of  sulphurous  acid  (50  c.  c.  corresponding  to  12 '94  c.  c.  iodine  solu- 
tion). After  addition  of  starch  paste,  iodine  solution  was  added  until  the  fluid 
appeared  blue. 


598 


EXPERIMENTS* 


This  required, — 


In  4 09 
b,  3 95 
6,  4 0(5 


d,  3-95 

As  100  c.  c.  of  iodine  solution  contained  0*58043  grm.  iodine,  this  gives — 


For  a,  0 0256  Cu  instead  of  0 0254 
“ b,  0-0260  “ 

“ c , 0 0257  “ “ 

“ 0 0260  “ “ 


Another  experiment,  made  with  100  c.  c.  of  the  same  solution  of  sulphate  of 
copper,  gave  0 "2606  instead  of  0 254  of  copper.  Nitrate  of  ammonia  having  been 
added  to  10  c.  c.  of  the  solution  of  sulphate  of  copper,  then  some  dilute  hydro- 
chloric acid,  3 -4  and  3 5 c.  c.  of  iodine  solution  were  required  instead  of  4 c.  c., — 
a proof  that  considerably  more  iodine  had  separated  than  corresponded  to  the 
oxide  of  copper. 


82.  Action  op  Solution  of  Cyanide  of  Potassium  upon  Ammoniacal 
Solution  of  Oxide  of  Copper  (to  § 119,  4,  b). 


a.  Three  10  c.  c.’s  of  a solution  of  sulphate  of  copper,  each  10  c.  c.  containing 
0 ‘I  grm.  sulphate  of  copper,  were  mixed  with  increasing  quantities  of  a solution 
of  ammonia,  and  a sufficient  amount  of  water  to  equalize  the  degree  of  concen- 
tration in  the  three  portions.  Solution  of  cyanide  of  potassium  was  then  added, 
drop  by  drop,  until  the  blue  color  had  disappeared.  This  required  the  following 
quantities : — 


Solution  of  sulphate 
of  copper. 

10  C.  C. 

1 0 c.  c. 

10  c.  c. 


Solution  of 
ammonia. 

4 c.  c. 

8 c.  c. 
16  c.  c. 


Water. 
12  c.  e. 
8 c.  e. 
0 c.  c. 


Solution  of  cyanide 
of  potassium. 

6-7 

6- 85 

7- 1 


Neutral  salts  of  ammonia  also  exercise  some  influence,  as  the  following  experi- 
ments show,  which  were  made  the  next  day  with  the  same  solutions  : — 


Sol.  CuO,  s O3. 
10  c,  c. 

10  c.  c. 

10  c.  c. 

10  c.  c. 


Sol.  N H3. 
2 c.  c. 
2 c.  c. 

6 c.  c. 
2 c.  c. 


Water,  &c. 

Sol.  K Cy. 

14  c.  c. 

6-70 

14  c.  c.  sol.  N H4  Cl  (1 : 10) 

7-40 

I 10  c.  c.  water,  ) 

> 4 c.  c.  S (Mil.  (1:5) 

7 00 

; 8 c.  c.  N H 4 O,  N 05  (1 : 10) ) 
1 6 c.  c.  water  ) 

• 7 30 

b.  Several  10  c.  c.’s  of  solution  of  sulphate  of  copper,  each  10  c.  c.  containing 
0 1 grm.  of  the  salt,  were  mixed  with  10  c.  c.’s  of  a solution  of  sesquicarbonate 
of  ammonia  (1  : 10),  and  after  addition  of  water  or  of  solution  of  neutral  ammo- 
nia salts,  cyanide  of  potassium  solution  was  added  till  the  blue  color  had  vanished 
Temp.  60°. 


c.  c.  CuO,  SO3 

c.  c.  2NH4  O,  3 coa 

c.  c.  Water,  &e. 

c.  c.  K Cy. 

10 

10 

10.  water 

j i.  16  4 
( ii.  16-6 

10 

10 

10.  NH40,SO3  (1:10) 

j i.  16-9 
} ii.  17-1 

10 

10 

10.  NH40,  N05  (1 : 10) 

j i.  17  0 
) ii.  17  1 

10 

10 

10.  NH4  Cl  (1:  10) 

j i.  17  1 
l ii.  17-1 

The  addition  of  the  2 drops  of  ferrocyanide  of  potassium  does  not  much  assist 
one  in  hitting  the  end-reaction,  as  the  solution,  which  towards  the  end  is  colored 
red,  gradually  becomes  light  yellow  when  more  cyanide  is  added,  and  is  not  fully 
decolorized  till  a further  addition  of  the  same  salt  has  been  made,  and  it  has  stood 
for  some  time. 


83.  Precipitation  of  Nitrate  of  Bismuth  by  Carbonate  of  Ammonia 
(to  § 120,  1,  a). 

If  a solution  of  nitrate  of  bismuth,  no  matter  whether  containing  much  or  little 


EXPERIMENTS. 


599 


free  nitric  acid,  is  mixed  with  water,  precipitated  with  carbonate  of  ammonia  and 
ammonia,  and  filtered  without  applying1  heat,  the  filtrate  acquires,  upon  addition 
of  sulphuretted  hydrogen  water,  a blackish-brown  color.  But  if  the  mixture  be- 
fore filtering1  is  heated  for  a short  time  nearly  to  boiling,  sulphuretted  hydrogen 
fails  to  impart  this  color  to  the  filtrate,  or,  at  all  events,  the  change  of  color  is 
hardly  visible  to  the  eye  looking  through  the  full  test-tube  from  the  top. 

84.  Determination  of  Antimony  as  Sulphide  (to  § 125,  1). 

0'559  grm.  of  pure  air-dried  tartar  emetic,  treated  according  to  § 125,  1,  gave 
0‘2902  grm.  tersulphide  of  antimony  dried  at  100°,=  ‘2492  grm.  or  44  58  per  cent, 
of  teroxide  of  antimony.  Heated  to  blackening  in  a current  of  carbonic  acid,  the 
precipitate  lost  0 0079  grm.  (reckoned  from  a part  to  the  whole),  leaving  accor- 
dingly 0 2823  grm.  of  anhydrous  tersulphide  of  antimony,  which  corresponds  to 
0 ‘24245  grm.  or  43 ‘37  per  cent,  of  teroxide  of  antimony.  As  the  tartar  emetic 
contains  43  ‘70  per  cent,  of  teroxide  of  antimony,  the  process  gives,  if  the  precip- 
itate is  dried  at  100°,  102  01 ; if  heated  to  blackening,  99  ‘22  instead  of  100. 

89.  Determination  of  Phosphoric  Acid  as  Pyrophosphate  of  Mag- 
nesia (to  § 134,  b , a). 

1‘9159  and  2 ’0860  grm.  pure  crystallized  phosphate  of  soda,  treated  as  directed 
§ 134,  5,  «,  gave  0‘5941  and  0‘6494  grm.  of  pyrophosphate  of  magnesia  respec- 
tively. These  give  19 ‘83  and  19 ‘91  per  cent,  of  phosphoric  acid  in  phosphate  of 
soda,  instead  of  19 ‘83  per  cent. 

90.  Determination  of  Phosphoric  Acid  as  Phosphate  of  Sesquioxide 
of  Uranium  (to  § 134,  c). 

30  c.  c.  of  a solution  of  pure  phosphate  of  soda,  treated  with  sulphate  of  mag- 
nesia, chloride  of  ammonium,  and  ammonia,  as  directed  § 134,  b , «,  gave  0‘3269 
grm.  of  pyrophosphate  of  magnesia.  10  c.  c.  contained  accordingly  0 ‘06982  grm. 
of  phosphoric  acid. 

10  c.  c.  of  the  same  solution  were  then  precipitated  with  acetate  of  sesquioxide 
of  uranium  as  directed  § 134,  c.  The  ignited  precipitate  was  treated  with  a 
little  nitric  acid,  then  again  ignited  ; after  cooling,  it  weighed  0‘3478  grm.  cor- 
responding to  0 ‘06954  grm.  of  phosphoric  acid. 

91.  Determination  of  Free  Sulphuretted  Hydrogen  by  Means  of 
Solution  of  Iodine  (to  § 148,  I. , a). 

The  experiments  were  made  to  settle  the  following  questions : — 

a.  Does  the  quantity  of  iodine  required  remain  the  same  for  solutions  of  sul- 
phuretted hydrogen  of  different  degrees  of  dilution  ? 

b.  Does  the  equation  H S+I=H  I+S  really  represent  the  decomposition  which 
takes  place  ? 

The  sulphuretted  hydrogen  water  was  contained  in  a flask  closed  by  a doubly- 
perforated  cork  ; into  one  aperture  a siphon  with  pinchcock  was  fitted,  to  draw 
off  the  fluid ; into  the  other  aperture  a short  open  tube,  which  did  not  dip  into 
the  fluid. 

Question  a. 

a.  About  30  c.  c.  of  iodine  solution  were  introduced  into  a flask,  which 
was  then  tared  ; sulphuretted  hydrogen  water  was  added  until  the  yellow  color 
had  just  disappeared.  The  flask  was  then  closed,  weighed,  starch  paste  added, 
and  then  solution  of  iodine  until  the  fluid  appeared  blue. 

70 ‘2  grm.  H S water  required  23 ‘4  c.  c.  iodine  solution,  100  accordingly 
33*33  c.  c. 

68 '4  grm.  required  22 ‘7  c.  c.  iodine  solution,  100  accordingly  33 ‘20  c.  c. 

P.  Same  process ; but  the  fluid  was  diluted  with  water  free  from  air. 

61*5  grm.  H S water  + 200  grm.  water  required  20 ‘7  c.  c.  iodine  solution, 
100  accordingly  33 ‘65  c.  c. 

52 ‘4  grm.  4- 400  grm.  water  required  17 ‘7  c.  c.  iodine  solution,  100  accord- 
ingly 33‘77. 

The  iodine  solution  contained  0 ‘00498  iodine  in  1 c.  c.  Considering  that 
addition  of  a larger  volume  of  water  necessarily  involves  a slight  increase  in  the 
quantity  of  iodine  solution,  these  results  may  be  considered  sufficiently  corre- 
sponding. 


600 


EXPERIMENTS. 


Question  b. 

According  to  a,  100  grm.  of  the  H S water  contained  0 '02215  grm.  H S,  assum- 
ing the  proportion  to  be  100 : 33  2. 

173 '6  grm.  of  the  same  water  were,  immediately  after  the  experiments  in  a , 
drawn  off  into  a hydrochloric  acid  solution  of  arsenious  acid  ; after  24  hours,  the 
tersulphide  of  arsenic  acid  was  filtered  off,  dried  at  100°,  and  weighed.  0 0920 
grm.  were  obtained,  which  corresponds  to  0 '03814  H S,  or  a percentage  of 
0-02197. 

The  second  question  also  is  therefore  answered  in  the  affirmative. 

92.  Solution  of  Chloride  of  Magnesium  dissolves  Oxalate  of  Lime 
(to  § 154,  6). 

If  some  chloride  of  calcium  is  added  to  a solution  of  chloride  of  magnesium, 
then  a little  oxalate  of  ammonia,  no  precipitate  is  formed  at  first ; but  upon 
slightly  increasing  the  quantity  of  oxalate  of  ammonia,  a trifling  precipitate 
gradually  separates  after  some  time. 

If  an  excess  of  oxalate  of  ammonia  is  added,  the  whole  of  the  lime  is  thrown 
down,  but  the  precipitate  contains  also  oxalate  of  magnesia.  This  shows  that  to 
effect  the  separation  of  the  two  bases  by  oxalate  of  ammonia,  the  reagent  must 
be  added  in  excess  ; whilst,  on  the  other  hand,  in  the  presence  of  much 
magnesia,  the  operator  must  expect  to  precipitate  some  of  the  magnesia,  as  the 
following  experiments  (No.  93)  clearly  show. 

93.  Separation  of  Lime  from  Magnesia  (to  § 154,  6). 

The  fluids  employed  in  the  following  experiments  were,  a solution  of  chlo- 
ride of  calcium,  10  c.  c.  of  which  corresponded  to  0*5618  Ca  O,  C 02  ; a solu- 
tion of  chloride  of  magnesium,  containing  0'250  Mg  O in  10  c.  c.  ; a solution  of 
chloride  of  ammonium  (1  : 8)  ; solution  of  ammonia,  containing  10  per  cent.  N 
H3 ; solution  of  oxalate  of  ammonia  (1  : 24)  ; acetic  acid,  containing  30  per  cent. 
A,  II  O. 

The  precipitation  was  effected  at  the  common  temperature  ; the  precipitate 
of  oxalate  of  lime  was  filtered  off  after  20  hours. 

a.  Influence  of  the  degree  of  dilution. 

a.  10  c.  c.  Mg  Cl,  10  c.  c.  Ca  Cl,  10  c.  c.  N H4  Cl,  4 drops  N H40,  50  c.  c. 
water,  20  c.  c.  2 N H4  O,  6.  Result,  0'5705  Ca  O,  C 02. 

/ 3 . Same  as  a,  with  150  c.  c.  water  instead  of  50  c.  c.  Result,  0'5670  Ca 
O,  C Oa. 

b.  Influence  of  excess  of  ammonia. 

Same  as  «,  /?  + 10  c.  c.  N II  O.  Result,  0'5614  grm.  Ca  O,  C 02. 

c.  Influence  of  excess  of  chloride  of  ammonium. 

Same  as  a , /?- (-40  c.  c.  N H4C1.  Result,  0 5652  grm. 

d.  Influence  of  excess  of  ammonia  and  chloride  of  ammonium. 

Same  as  a , 0+ 30  c.  c N H4C1+10  c.  c.  N II40.  Result,  0'5613  grm. 

e.  Influence  of  free  acetic  acid.  _ 

Same  as  a,  /?,  only  with  6 drops  A,  instead  of  the  4 drops  N H40.  Result, 
Q'5594  grm. 

/.  Influence  of  excess  of  oxalate  of  ammonia,  in  feebly  alkaline  solution. 

Same  as  a,  /?+20  c.  c.  2 NH,  O,  O.  Result,  0'5644  grm.  Ca  O,  C 02. 

g.  Influence  of  excess  of  oxalate  of  ammonia,  in  strongly  alkaline  solution 

Same  as  a , 0,  + lO  c.  c.  NH4O  + 20  c.  c.’2  N H40.  O.  Result,  0.5644. 

h.  Influence  of  excess  of  oxalate  of  ammonia,  in  presence  of  much  N H4C1  and 

NHiO. 

Same  as  a , 0,  +10  N H4  0+30  N H4Cl+20  2 N H40,  O.  Result,  0'5709 
grm. 

i.  Influence  of  excess  of  oxalate  of  ammonia,  in  solution  slightly  acidified 

with  A. 

Same  as  «,  /?, — 4 drops  N H40  + 6 drops  A+20  c.  c.  2 N H40,  O.  Result, 
0'5661  grm. 

Consequently,  when  a notable  amount  of  magnesia  is  present  there  is  always  a 
chance  of  oxalate  of  magnesia,  or  oxalate  of  magnesia  and  ammonia  precipitating 
along  with  the  oxalate  of  lime. 


EXPERIMENTS. 


601 


Another  series  of  experiments  in  which  a solution  of  oxalate  of  magnesia  in' 
hydrochloric  acid  was  mixed  with  ammonia  under  varying  circumstances,  proved 
also  that,  in  presence  of  a notable  quantity  of  magnesia,  oxalate  of  magnesia,  or 
oxalate  of  magnesia  and  ammonia,  will  always  separate  after  standing  for  some 
time,  no  matter  whether  in  a cold  or  a warm  place. 

In  a third  series  of  experiments,  the  separation  was  effected  by  double  precip- 
itation, in  accordance  with  29-  The  same  solutions  were  employed  as  in  the 
first  series,  with  the  exception  of  the  chloride  of  magnesium,  for  which  a solu- 
tion was  substituted  containing  02182  grm.  Mg  0,  in  10  c.  c. 

10  c.  c.  CaCl  + 30  c.  c.  Mg  Cl, +20  c.  c.  NH4C1, +300  c.  c.  water, +6  drops 
ammonia,  + a sufficient  excess  of  oxalate  of  ammonia.  Results,  in  two  experi- 
ments, 0*5621  and  0*5652,  mean  0*5636,  instead  of  0*5618  Ca  O,  C02 ; also  0 6660 
and  0*6489  Mg  O,  mean  0*6574,  instead  of  0*6546. 

94.  Separation  of  Iodine  from  Chlorine  by  Pisani’s  Method  (to  § 169, 

204). 

0*2338  grm.  iodide  of  potassium,  dissolved  in  water,  +-£- c.  c.  of  solution  of 
iodide  of  starch,  required  14  c.  c.  of  decinormal  silver  solution  = 0*2322  grm. 
iodide  of  potassium. 

0*3025  grm.  iodide  of  potassium,  mixed  with  about  double  the  quantity  of 
chloride  of  sodium,  required  18*2  c.  c.  silver  solution =0*3021  K I. 

0*2266  grm.  iodide  of  potassium,  mixed  with  about  100  times  as  much  chloride 
of  sodium,  required  13*7  c.  c.  silver  solution  = 0*2272  K I. 

95.  Separation  of  Iodine  from  Bromine,  by  Pisani’s  Method  (to  § 169, 

209). 

0*3198  grm.  iodide  of  potassium,  mixed  with  double  the  quantity  of  bromide 
of  potassium,  required  19*2  c.  c.  of  decinormal  silver  solution  = 0*3187  K I. 

99.  Chlorimetrical  Experiments  (to  § 213). 

1 0 grm.  of  chloride  of  lime  were  rubbed  up  with  water  to  one  litre,  with  which 
the  following  experiments  were  made  : — 

a.  By  Penot’s  method  (§  212);  obtained  23*5  and  23  *5  per  cent. 

b.  By  means  of  iron  (§  213,  modification) ; obtained  23  *6  per  cent. 

c.  By  Bunsen’s  method  (p.  508,  C) ; results,  23*6 — 23*6  per  cent. 

100.  Drying  of  Manganese  (to  § 214, 1.) 

Four  small  pans,  containing  each  8 grm.  of  manganese  of  53  per  cent. , were 
first  heated  in  the  water-bath.  After  3 hours,  I.  had  lost  0*145  ; after  6 hours, 
II.  0*15;  after  9 hours,  III.  0*15;  after  12  hours,  IV.  015.  grm.  I.  and  II. 
having  been  left  standing,  loosely  covered,  in  the  room  for  12  hours,  II.  was 
found  to  weigh  exactly  as  much  as  at  first ; I.  wanted  only  0 *01  grm.  of  the  ori- 
ginal weight. 

The  four  pans  were  now  heated  for  two  hours  to  120°.  After  cooling,  they 
were  found  to  have  lost  each  0*180  of  the  original  weight.  I.  and  II.  having 
been  left  standing,  loosely  covered,  in  the  room  for  60  hours,  were  found  to  have 
again  acquired  their  original  weight  by  attracting  moisture.  III.  and  IV.  were 
heated  for  2 hours  to  150°.  The  loss  of  weight  in  both  cases  was  0*215  grm. 
Having  been  left  standing,  loosely  covered,  in  the  room  for  72  hours,  both  were 
found  to  weigh  0 *05  less  than  at  first.  Assuming  the  hygroscopic  moisture  ex- 
pelled to  be  re-absorbed  by  standing  in  the  air,  this  shows  that  at  150°  a little 
chemically  combined  water  escapes  along  with  the  moisture,  and  accordingly 
that  the  temperature  must  not  exceed  120°. 

My  experiments  will  be  found  described  in  detail  in  Dingler’s  polyt.  Journ., 
135,  277  et  seq. 


TABLE  I, 


603 


TABLES  FOB  THE  CALCULATION  OF  ANALYSES. 


TABLE  I. 


EQUIVALENTS  OF  THE  ELEMENTS  CONSIDERED  IN  THE  PRESENT  WORK.* 

(Dumas) 

(Dumas) 

(Pelouze,  Berzelius) 

(Dumas) 

(Schneider) 

(Berzelius) 

(Marignac) 

(C.  v.  Hauer) 

(Johnson  and  Allen,  Bunsen) 
(Dumas,  Erdmann  and  Marchand) 
(Dumas,  Erdmann  and  Marchand) 
(Marignac,  Stas) 

(Berlin,  Peligot) 

(Rothoff,  Dumas) 

(Erdmann  and  Marchand) 

(Louyet) 

(Comp.  Strecker,  loc.  cit.) 

(Dumas) 

(Marignac,  Dumas) 

(Erdmann  and  Marchand) 
(Berzelius,  Dumas) 

(C.  Diehl,  Troost) 

(Marchand  and  Scheerer) 

(v.  Hauer,  Dumas) 

(Erdmann  and  Marchand) 

(Berlin) 

(Rothoff,  Marignac,  Dumas) 
(Marignac) 

(Berzelius,  comp.  Strecker,  loc. cit.) 
(Schrotter) 

(Andrews) 

(Marignac,  Stas) 

(Bunsen,  Piccard) 

( (Berzelius,  Sacc,  Erdmann,  and 
l Marchand — mean) 

(Dumas)  • 

(Marignac) 

(Pelouze,  Stas) 

(Dumas) 

(Erdmann  and  Marchand) 
(Crookes) 

(Dumas) 

(Pierre) 

J[(Ebelmen) 

(Axel  Erdmann) 


Aluminium 

A1 

13  75 

Antimony- 

Sb 

122-00 

Arsenic 

As 

75-00 

Barium 

Ba 

68-50 

Bismuth 

Bi 

208 -00f 

Boron 

B 

1100 

Bromine 

Br 

80-00 

Cadmium 

Cd 

56  00 

Caesium 

Cs 

133  00 

Calcium 

Ca 

20-00 

Carbon 

C 

6-00 

Chlorine 

Cl 

35-46 

Chromium 

Cr 

26-24 

Cobalt 

Co 

29  *50f 

Copper 

Cu 

31-70 

Fluorine 

FI 

19  00 

Gold 

Au 

196  00 

Hydrogen 

H 

100 

Iodine 

I 

127-00  i 

Iron 

Fe 

28-00  i 

Lead 

Pb 

103-50  i 

Lithium 

Li 

7-00  i 

Magnesium 

Mg 

12-00  ( 

Manganese 

Mn 

27-50 

Mercury 

Hg 

100  00  i 

Molybdenum 

Mo 

46-00||  i 

Nickel 

Ni 

29*501 

Nitrogen 

N 

1400 

Oxygen 

O 

8-00 

Palladium 

Pd 

53  00 

Phosphorus 

P 

3100 

Platinum 

Pt 

98-94 

Potassium 

K 

39-11 

Rubidium 

Rb 

85-40 

Selenium 

Se 

39-5** 

Silicon 

Si 

14 -00ff 

Silver 

A g 

107-97 

Sodium 

Na 

23  00 

Strontium 

Sr 

43-75 

Sulphur 

S 

16-00 

Thallium 

T1 

203-00# 

Tin 

Sn 

59-0011 

Titanium 

Ti 

25-0.0 

Uranium 

Ur 

59-4011 

Zinc 

Zn 

32-53 

* It  has  been  necessary  to  alter  the  numbers  in  some  cases  where  no  new  special  experiments  have 
been  made.  This  arose  from  the  fact  that  the  numbers  in  question  were  deduced  from  other  equiva- 
lents which  have  since  been  corrected.  Those  who  are  curious  in  the  matter  of  equivalents  should  re- 
fer to  Handworterbuch  der  reinen  und  angewandten  Chemie,  2 Aufl.  Bd.  II.  463,  article  Atomge- 
wichte,  by  A.  Strecker.  With  respect  to  the  equivalents  that  have  recently  been  redetermined,  comp. 
Zeitschrift  f.  Anal.  Chem. 

+ Dumas  makes  210  00.  % W.  J.  Russell  found  29-37.  (Joum.  Chem.  Soc.  (2).  I.  61.) 

j|  Dumas  makes  it  48-00.  T W.  J.  Russell  found  29-37  (loc.  cit.). 

**  Dumas  found  39-75.  ft  Silicic  Acid=Si  0-2.  XX  After  Lamy  204-00. 

Ill  After  Mulder  58-00.  ITT  Comp.  p.  141,  note  +. 


604 


TABLE  II. 


TABLE  IL 

COMPOSITION  OF  THE  BASES  AND  OXYGEN  ACIDS. 


Csesia 

• Cs  . . 

O . . 

. 133-00  . 
. 8-00  . 

. 94-33 
. 5-67 

Cs  O . 

. 141-00  . 

. 100  00 

Rubidia 

Rb  . . 

O . . 

. 85-40  . 
. 800  . 

. 91  -43 
. 8-57 

RbO  . 

. 93-40  . 

. 100-00 

Potassa 

K . . 

O . . 

. 39-11  . 

. 8-00  . 

. 83-02 
. 16-98 

KO . . 

. 4711  . 

. 100  00 

Soda 

Na  . \ 

O . . 

. 23  00  . 
. 8-00  . 

. 74  19 
• 25*81 

Na  O . 

. 31-00  . 

. 100  00 

Lithia 

Li  . . 

O . . 

. 7-00  . 

. 8-00  . 

. 46-67 
. 53-33 

LiO  . 

. 15  00  . 

. 100-00 

Oxide  of  Ammonium 

NH4  . 
O . . 

. 18-00  . 
. 8 00  . 

. 69-23 
. 30-77 

nh4o  . 

. 26-00  . 

. 100-00 

Group  II. 
Baryta 

Ba  . 

O . . 

. 68-50  . 
. 8-00  . 

. 89-54 
. 10-46 

Ba  O . 

. 76-50  . 

. 100  00 

Strontia 

Sr  . . 

O . . 

. 43-75  . 
. 8 00  . 

. 84-54 
. 15-46 

SrO  . 

. 51-75  . 

. 100-00 

Lime 

Ca  . . 

O . . 

. 20  00  . 
. 800  . 

CO  l> 

*P 

^ 00 

Ca  O . 

. 28-00  . 

. 10000 

Magnesia 

Mg.  . 
O . . 

. 12  00  . 

. 8 00  . 

. 60-03 

. 39-97 

Mg  0 . . 20  00  . . 100*00 


TABLE  II, 


605 


Group  III. 


Alumina 

Al2  . . 

. 27-50 

. 

. 53-40 

03  . . 

. 24-00 

. 46-60 

AI2O3  . 

. 51*50 

• 

. 100-00 

Sesquioxide  of  Chromium 

Cr2 

. 52-48 

. 68-62 

03  . . 

. 24-00 

. 31-38 

Cr203  . 

. 76-48 

• 

• 100  00 

Group  IY. 

Oxide  of  Zinc 

Zn  . 

. 32-53 

. 80-26 

0 . . 

. 8 00 

. 

. 19-74 

ZnO  . 

. 40-53 

. 100-00 

Protoxide  of  Manganese 

Mn  . 

. 27-50 

. 77-46 

0 . . 

. 8-00 

. 22-54 

Mn  0 . 

. 35-50 

. 100-00 

besquioxide  of  Manganese 

Mn2 

. 55  00 

. 69-62 

03  . . 

. 24-00 

. 30-38 

Mn203  . 

. 79  00 

• 

. 100  00 

Protoxide  of  Nickel 

Ni  . . 

. 29-50 

. 78-67 

0 . . 

. 8 00 

. 

. 21-33 

NiO  . 

. 37-50 

• 

. 100-00 

Protoxide  of  Cobalt 

Co  . 

. 29-50 

. 78-67 

0 . . 

. 8-00 

. 21-33 

CoO  . 

. 37  50 

. 100-00 

Sesquioxide  of  Cobalt 

Co2  . 

. 59-00 

. 71-08 

03  . . 

. 24  00 

• 

. 28-92 

C00O3  . 

. 83-00 

• 

. 100  00 

Protoxide  of  Iron 

Fe  . . 

. 28-00 

. 77-78 

0 . . 

. 8 00 

. 22-22 

FeO  . 

. 36  00 

. 100-00 

Sesquioxide  of  Iron 

Fe2  . . 

. 56-00 

. 70  00 

03  . . 

. 24-00 

. 30-00 

Fe203  • 

. 80-00 

• 

. 100-00 

Group  V. 

Oxide  of  Silver 

A g . . 

. 107-97 

. 

. 93  10 

0 . . 

. 8 00 

. 6-90 

AgO  . 

. 115-97 

. 100  00 

606 


TABLE  II. 


Oxide  of  Lead 

Pb  . 

. 103  50  . 

. 92-83 

0 . 

. 800  . 

. 717 

PbO 

. 111-50  . 

. 100  00 

Suboxide  of  Mercury 

Hg2 

. 200  00  . 

. 96-15 

0 . 

. 8 00  . 

. 3-85 

Hg20 

. 208-00  . 

. 100-00 

Oxide  of  Mercury 

Hg 

. 100  00  . 

. 92-59 

0 . 

. 8-00  . 

. 7-41 

HgO 

. 108  00  . 

. 100-00 

Suboxide  of  Copper 

Cu2 

. 63-40  . 

. 88-80 

0 . 

. 8-00  . 

. 11  -20 

Cu20 

. 71-40  . 

. 100  00 

Oxide  of  Copper 

Cu. 

. 31-70  . 

. 79-85 

0 . 

. 8 00  . 

. 20-15 

- 

CuO 

. 39-70  . 

. 100  00 

Teroxide  of  Bismuth 

Bi  . 

. 208-00  . 

. 89-66 

o3  • 

. 24-00  . 

. 10-34 

Bi03 

. 232-00  . 

. 100  00 

Oxide  of  Cadmium 

Cd  . 

. 56*00  . 

. 87-50 

0 . 

. 8 00  . 

. 12-50 

CdO 

# 

. 64  00  . 

. 100-00 

Group  VI. 
Teroxide  of  Gold 


Binoxide  of  Platinum 


Teroxide  of  Antimony 


Protoxide  of  Tin 


Au 

. 196-00  . 

. 89  09 

03  . . 

. 24  00  . 

. 10-91 

Au03  . 

. 220  00  . 

. 100  00 

Pt  . . 

. 98  94  . 

. 86-08 

02  . . 

. 16  00  . 

. 13-92 

Pt  02  . 

. 114-94  . 

. 10000 

Sb  . . 

. 122-00  . 

. 83-56 

Os  . . 

. 24-00  . 

. 16-44 

Sb03  . 

. 146-00  . 

. 100-00 

Sn  . . 

. 59  00  . 

. 88-06 

O . . 

. 8 00  . 

. 11-94 

SnO  . 

. 67  00  . 

. 100-00 

Sn  . . 

. 59  00  . 

. 78-67 

O.  . . 

. 16  00  . 

. 21-33 

SnO.  . 

. 75-00 

. 100  00 

Binoxide  of  Tin 


Arsenious  acid 


TABLE  II. 


607 


Arsenic  acid 


Chromic  acid 


Sulphuric  acid 


Phosphoric  acid 


Boracic  acid 


Oxalic  acid 


Carbonic  acid 


Silicic  acid 


Nitric  acid 


As  . 

03  . . 

. 75-00  . 
. 24-00  . 

. 75-76 
. 24-24 

As03  . 

. 99-00  . 

. 100-00 

As  . . 

. 75  00  . 

. 65-22 

06.  . 

. 40-00  . 

. 34-78 

As06  . 

. 115-00  . 

. 100  00 

b.  ACIDS. 

Cr  . . 

. 26-24  . 

. 52-23 

03  . . 

. 24  00  . 

. 47-77 

Cr03  . 

. 50  24  . 

. 100  00 

S . . 

. 16  00  . 

. 40-00 

03  . . 

. 24-00  . 

. 60.00 

S03  . 

. 40  00  . 

. 100  00 

P . . 

. 3100  . 

. 43-66 

05  . . 

. 40-00  . 

. 56-34 

P06  . 

. 7100  . 

. 100-00 

B . . 

. 1100  . 

. 31-43 

03  . . 

. 24-00  . 

. 68-57 

B03  . 

. 35-00  . 

. 100-00 

C4  . 

. 24-00  . 

. 33-33 

06  . . 

. 48  00  . 

. 66-67 

c4o8  . 

. 72-00  . 

. 100-00 

c . . 

. 600  . 

. 27-27 

02  . . 

. 16  00  . 

. 72-73 

co2  . 

. 22  00  . 

. 100  00 

Si  . . 

. 14-00  . 

. 46-67 

02  . . 

. 16-00  . 

. 53-33 

Si  02  • 

. 30-00  . 

. 100-00 

N . . 

. 14-00  . 

. 25-93 

05  . . 

. 40  00  . 

. 74-07 

NOs  . 

. 54-00  . 

. 100  00 

Cl  . . 

. 35-46  . 

. 46-99 

06  . . 

. 40-00  . 

. 53  01 

CIO,  . 

. 75-46  . 

. 10000 

Chloric  acid 


608 


TABLE  III, 


TABLE  III. 


REDUCTION  OF  COMPOUNDS  FOUND  TO  CONSTITUENTS  SOUGHT  BY  SIMPLE 
MULTIPLICATION  OR  DIVISION. 


This  Table  contains  only  some  of  the  more  frequently  occurring1  compounds ; 
the  formulae  preceded  by  ! give  absolutely  accurate  results.  The  Table  may 
also  be  extended  to  other  compounds,  by  proceeding  according  to  the  instruc- 
tions given  in  § 199. 


! Carbonate  of  lime  x 0 ’44= Carbonic  acid. 

CHLORINE. 

Chloride  of  silver  x 0 '24724= Chlorine. 

COPPER. 

Oxide  of  copper  xO '79849= Copper. 

IRON. 

! Sesquioxide  of  iron  xO '7 =2  Iron. 

! Sesquioxide  of  iron  xO  '9 =2  Protoxide  of  iron. 

LEAD. 

Oxide  of  lead  x 0 '9283 =Lead. 

MAGNESIA. 

Pyrophosphate  of  magnesia  x 0 '36036=2  Magnesia. 

MANGANESE. 

Protosesquioxide  of  manganese  x 0*72052=3  Manganese. 
Protosesquioxide  of  manganese  x 0 '93013 =3  Protoxide  of  manganese. 


Pyrophosphate  of  magnesia  x 0 '6396= Phosphoric  acid. 

Phosphate  of  sesquioxide  of  uranium  (2  Ur2  03,  P05)  x 0'1991=Phosphonc 
acid. 

POTASSA. 

Chloride  of  potassium  x 0 '52445=  Potassium. 

Sulphate  of  potassa  x 0'5408=Potassa. 

Potassio-bichloride  of  platinum  x 0 '30507 


FOR  INORGANIC  ANALYSIS. 


CARBONIC  ACID. 


PHOSPHORIC  ACID. 


or 

Potassio-bichloride  of  platinum 
3'278 


TABLE  III. 


C09 


Potassio -bichloride  of  platinum  x 0*19272> 
or 

Potassio -bichloride  of  platinum 
5188 


=Potassa. 


SODA. 


Chloride  of  sodium  x 0 5302= Soda. 
Sulphate  of  soda  x 0*43658=:  Soda. 


SULPHUR. 

Sulphate  of  baryta^  0*13734= Sulphur. 


SULPHURIC  ACID 

Sulphate  of  baryta  x 0*34335= Sulphuric  acid. 


FOR  ORGANIC  ANALYSIS, 


CARBON. 


Carbonic  acid  x 0*2727 
or 

Carbonic  acid 
3t666 


= Carbon. 


or 

Carbonic  acid  x 3 

lT 


HYDROGEN. 

Water  x 0*11111  'I 

Water  f =Hydrogen. 

9 J 

NITROGEN. 

Ammonio -bichloride  of  platinum  x 0*06269= Nitrogen. 
Platinum  x 0*1415=Nitrogen. 

39 


610 


TABLE  IV. 


TABLE 

Showing  the  Amount  of  the 
Number  of  the 


Elements. 

Found. 

Sought. 

1 

Aluminium . . 

Alumina 

Aluminium 

0-53398 

Al,  03 

Ala 

(Ammonium) 

Chloride  of  ammonium 

Ammonia 

0-31804 

NH4  Cl 

nh3 

Ammonio-bichloride  of  platinum 

Oxide  of  ammonium 

0-11644 

N H4  Cl,  Pt  Cl„ 

N H4  0 

Ammonio-bichloride  of  platinum 

Ammonia 

0 07614 

N H,  Cl,  Pt  Cla 

nh3 

Antimony.  . . 

Teroxide  of  antimony 

Antimony 

0-83562 

Sb  03 

Sb 

Tersulphide  of  antimony 

Antimony 

0-71765 

Sb  S3 

Sb 

Tersulphide  of  antimony 

Teroxide  of  antimony 

0-85882 

Sb  S3 

Sb  03 

Antimonious  acid 

Teroxide  of  antimony 

0-94805 

Sb  04 

Sb  03 

Arsenic 

Arsenious  acid 

Arsenic 

0-75758 

As  03 

As 

Arsenic  acid 

Arsenic 

0-65217 

As  05 

As 

Arsenic  acid 

Arsenious  acid 

0-86087 

As  05 

As  03 

Tersulphide  of  arsenic 

Arsenious  acid 

0-80488 

As  S3 

As  03 

Tersulphide  of  arsenic 

Arsenic  acid 

0-93496 

As  S3 

As  05 

Arseniate  of  ammonia  and  magnesia 

Arsenic  acid 

0-60526 

2 Mg  0,  N Ht  0,  As  05  + aq 

As  05 

Arseniate  of  ammonia  and  magnesia 

Arsenious  acid 

0 52105 

2 Mg  0,  N H4  0,  As  05  + aq 

As  03 

Barium 

Baryta 

Barium 

0-89542 

Ba  0 

Ba 

Sulphate  of  baryta 

Baryta 

0-65665 

Ba  0,  S 03 

Ba  0 

Carbonate  of  baryta 

Baryta 

0-77665 

Ba  0,  C 02 

Ba  0 

Silico-fluoride  of  barium 

Baryta 

0-54839 

Ba  FI,  Si  Fla 

Ba  0 

Bismuth 

Teroxide  of  bismuth 

Bismuth 

0-89655 

Bi  03 

Bi 

Boron 

Boracic  acid 

Boron 

0 31429 

B03 

B 

Bromine 

Bromide  of  silver 

Bromine 

0-42560 

Ag  Br 

Br 

Cadmium. . . . 

Oxide  of  cadmium 

Cadmium 

0-87500 

CdO 

Cd 

Calcium 

Lime 

Calcium 

0-71429 

CaO 

Ca 

Sulphate  of  lime 

Lime 

0-41176 

Ca  0.  S03 

Ca  0 

Carbonate  of  lime 

Lime 

0*56000 

Ca  0,  C 02 

Ca  0 

Carbon 

Carbonic  acid 

Carbon 

0-27273 

C O o. 

C 

TABLE  IV.  611 


IY. 

Constituent  sought  for  every 
Compound  found. 


2 

3 

4 

5 

6 

7 

8 

9 

1-06796 

1-60194 

2-13592 

2-66990 

3-20389 

3-73787 

4-27185 

4-80583 

0-63608 

0-95413 

1-27217 

1-59021 

1-90825 

2-22629- 

2-54433 

2-86237 

0-23288 

0-34932 

0-46576 

0-58220 

0-69864 

0-81508 

0-93152 

1-04796 

0-15228 

0-22842 

0-30456 

0-38070 

0-45684 

0-53299 

0*60913 

0-68527 

1-67123 

2-50685 

3-34247 

4-17808 

5-01370 

5-84932 

6-68194 

7-52055 

1-43529 

2-15294 

2-87059 

3-58834 

4-30588 

5-02353 

5-74118, 

6-45882 

1-71765 

2-57647 

3-43530 

4-29412 

5-15294 

6-01177 

6-87059 

7-72942 

1-89610 

2-84416 

3-79221 

4-74026 

5-68831 

6-63636 

7-58442 

8*53247 

1-51516 

2-27274 

3 03032 

3-78790 

4-54548 

5-30306 

6-06064 

6-81822 

1-30435 

1 -95652 

2-60870 

3-26087 

3-91304 

4-56522 

5-21739 

5-86957 

1-72174 

2-58261 

3-44348 

4-30435 

5-16521 

6-02608 

6-88695 

7-74782 

1-60975 

2-41463 

3-21951 

4-02439 

4-82927 

5-63415 

6-43902 

7-24390 

1-86992 

2-80488 

3-73984 

4-67480 

5-60975 

6-54471 

7-47967 

8-41463 

1 -21053 

1-81579 

2-42105 

3-02631 

3-63158 

4-23684 

4-84210 

5-44737 

1 -04210 

1-56316 

2-08421 

2-60526 

3-12631 

3-64736 

4-16842 

4-68947 

1-79085 

2-68627 

3-58170 

4-47712 

5 37255 

6-26797 

7*16340 

8-05882 

1-31330 

. 1-96996 

2-62661 

3-28326 

3-93991 

4-59656 

5-25322 

5-90987 

1-55330 

2-32995 

3-10660 

3-88325 

4-65990 

5-43655 

6-21320 

6-98985 

1-09677 

1-64516 

2-19355 

2-74194 

3-29032 

3-83871 

4-38710 

4-93548 

1-79310 

2-68965 

3-58620 

4-48275 

5-37930 

6-27586 

7-17240 

8-06895 

0-62857 

0-94286 

1 -25714 

1-57143 

1-88572 

2-20000 

2-51429 

2-82857 

0-85120 

1-27680 

1-70240 

2-12800 

2-55360 

2-97920 

3-40480 

3-83040 

^1  ’75000 

2-62500 

3-50000 

4-37500 

5-25000 

6-12500 

7-00000 

7 87500 

1-42857 

2-14286 

2-85714 

3*57143 

4-28571 

5-00000 

5-71429 

6-42857 

0-82353 

1 -23529 

1-64706 

2-05882 

2-47059 

2-88235 

3*29412 

3-70588 

1-12000 

1-68000 

2-24000 

2-80000 

3-36000 

3-92000 

4-48000 

5*04000 

0 54546 

0-81818 

1-09091 

1-36364 

1-63636 

1-90909 

2-18181 

2-45455 

612 


TABLE  IV. 


TABLE  IV. 


Elements. 

Found. 

Sought. 

1 

Carbon 

Carbonate  of  lime 

Carbonic  acid 

0-44000 

Ca  0,  C 02 

C 02 

Chlorine 

Chloride  of  silver 

Chlorine 

0-24724 

Ag  Cl 

Cl 

Chloride  of  silver 

Hydrochloric  acid 

0 25421 

Ag  Cl 

H Cl 

Chromium. . . 

Sesquioxide  of  chromium 

Chromium 

0 68619 

Cr2  O3 

Cr2 

Sesquioxide  of  chromium 

Chromic  acid 

1-31381 

Cr9  03 

2 Cr  03 

Chromate  of  lead 

Chromic  acid 

0-31062 

Pb  0,  Cr  03 

Cr  03 

Cobalt 

Cobalt 

Protoxide  of  cobalt 

1 -27119 

Co 

Co  0 

Sulphate  of  protoxide  of  cobalt 

Protoxide  of  cobalt 

0-48387 

Co  0,  S03 

Co  0 

Sulphate  of  cobalt  -f-  sulphate  of 

Protoxide  of  cobalt 

018015 

potassa 

2 Co  0 

2 (Co  0,  S O3)  + 3 (K  0 S03) 

1 

Sulphate  of  cobalt  + sulphate  of 

Cobalt 

0 14171 

potassa 

2 Co 

2 (Co  0,  S 03)  + 3 (K  0,  S03) 

Copper 

Oxide  of  copper 

Copper 

0-79849 

Cu  0 

Cu 

Subsulphide  of  copper 

Copper 

0-79849 

Cu2  S 

Cu2 

Fluorine 

Fluoride  of  calcium 

Fluorine 

0-48718 

Ca  FI 

FI 

Fluoride  of  silicon 

Fluorine 

0-73077 

Si  Fl„ 

Fla 

Hydrogen 

Water 

Hydrogen 

011111 

H 0 

H 

Iodine 

Iodide  of  silver 

Iodine 

0-54049 

Ag  I 

I 

Protiodide  of  palladium 

Iodine 

0-70556 

Pd  I 

I 

Iron 

Sesquioxide  of  iron 

Iron 

0-70000 

Fe2  O3 

Fe2 

Sesquioxide  of  iron 

Protoxide  of  iron 

0-90000 

Fe2  03 

2 Fe  0 

Sulphide  of  iron 

Iron 

0-63636 

Fe  S 

Fe 

Lead 

Oxide  of  lead 

Lead 

0-92825 

■ 

Pb  0 

Pb 

Sulphate  of  lead 

Oxide  of  lead 

0-73597 

Pb  0,  S 03 

Pb  0 

Sulphate  of  lead 

Lead 

0-68317 

Pb  0,  S 03 

Pb 

Sulphide  of  lead 

Oxide  of  lead 

0 93305 

Pb  S 

Pb  0 

Lithium. .... 

Carbonate  of  lithia 

Lithia 

0-40541 

Li  0,  C 02 

Li  0 

Sulphate  of  lithia 

Lithia 

0-27273 

Li  0,  S O3 

Li  0 

Basic  phosphate  of  lithia 

Lithia 

0 38793 

3 Li  0,  P 05 

3 Li  0 

TABLE  IV. 


613 


( continued ). 


2 

3 

4 

5 

6 

7 

8 

9 

0-88000 

1-32000 

1-76000 

2-20000 

2-64000 

3-08000 

3-52000 

3-96000 

0-49448 

0-74172 

0-98896 

1-23620 

1-48344 

1-73068 

1-97792 

2-22516 

0-50842 

0-76263 

1 -01684 

1-27105 

1-52526 

1-77947 

2 03368 

2-28789 

1-37238 

2-05858 

2-74477 

3-43096 

4-11715 

4-80334 

5-48954 

6*17573 

2-62762 

3-94142 

5-25523 

6-56904 

7-88285 

919666 

10-51046 

11-82427 

0-62124 

0-93187 

1 -24249 

1-55311 

1-86373 

2-17435 

2-48498 

2-79560 

2-54237 

3-81356 

5-08474 

6-35593 

7-62712 

8-89830 

10-16949 

11-44067 

0-96774 

1 -45161 

1-93548 

2-41935 

2-90323 

3-38710 

3-87097 

4-35484 

0-36029 

0-54044 

0-72058 

0-90073 

1-08088 

1 -26102 

1-44117 

1-62131 

0-28343 

0 42514 

0-56686 

0-70857 

0-85029 

0-99200 

1-13372 

1-27543 

1-59698 

2-39547 

3-19396 

3-99244 

4-79093 

5-58942 

6-38791 

7-18640 

1-59698 

2-39547 

3-19396 

3-99244 

4-79093 

5-58942 

6-38791 

7-18640 

0-97436 

1-46154 

1-94872 

2-43590 

2-92307 

3-41027 

3-89743 

4-38461 

1-46154 

2-19231 

2-92308 

3-65385 

4-38461 

5-11538 

5-84615 

6-57692 

0-22222 

0-33333 

0-44444 

0 55555 

0-66667 

0-77778 

0-88889 

1-00000 

1-08099 

1-62148 

2-16198 

2-70247 

3 24297 

3-78346 

4-32396 

4-86445 

1-41111 

2-11667 

2-82222 

3-52778 

4-23334 

4-93889 

5-64445 

6-35000 

1-40000 

.2-10000 

2 80000 

3-50000 

4-20000 

4-90000 

5-60000 

6-30000 

1-80000 

2-70000 

3-60000 

4-50000 

5-40000 

6-30000 

7-20000 

8-10000 

1 -27273 

1-90909 

2-54546 

3-18182 

3-81818 

4-45455 

5 09091 

5-72728 

1-85650 

2-78475 

3-71300 

4-64126 

5*56951 

6-49776 

7-42601 

8 35426 

1-47195 

2-20792 

2-94390 

3-67987 

4-41584 

5-15182 

5-88779 

6-62377 

1 -36634 

2-04950 

2-73267 

3-41584 

4-09901 

4-78218 

5-46534 

6-14851 

1-86611 

2-79916 

3-73222 

4-66527 

5-59832 

6-53138 

7-46443 

8-39749 

0-81081 

1-21622 

1-62162 

2-02703 

2-43243 

2-83784 

3-24324 

3-64865 

0-54545 

0-81818 

1-09091 

1 -36364 

1-63636 

1-90909 

2-18182 

2-45454 

0-77586 

1 -16379 

1-55172 

1-93966 

2-32759 

2-71552 

3-10345 

3-49138 

TABLE  IV. 


Elements. 

Found. 

Sought. 

1 

Magnesium. . 

Magnesia 

Magnesium 

0-60030 

Mg  0 

Mg 

Sulphate  of  magnesia 

Magnesia 

0-33350 

Mg  0,  S 03 

Mg  0 

Pyrophosphate  of  magnesia 

Magnesia 

0-36036 

2 Mg  0,  P 05 

2 Mg  0 

Manganese . . 

Protoxide  of  manganese 

Manganese 

0-77465 

MnO 

Mn 

Protosesquioxide  of  manganese 

Manganese 

0-72052 

Mn  0+Mn203 

Mn3 

Sesquioxide  of  manganese 

Manganese 

0 69620 

Mn2  03 

Mn2 

Sulphate  of  protoxide  of  manganese 

Protoxide  of  manganese 

0-47020 

Mn  0,  S 03 

Mn  0 

Sulphide  of  manganese 

Protoxide  of  manganese 

0 81609 

Mn  S 

Mn  0 

Sulphide  of  manganese 

Manganese 

0-63218 

Mn  S 

Mn 

Mercury 

Mercury 

Suboxide  of  mercury 

1 -04000 

Hg2 

Hg2  0 

Mercury 

Oxide  of  mercury 

1-08000 

Hg 

Hg  0 

Subchloride  of  mercury 

Mercury 

0-84940 

Hg2  Cl 

Hg2 

Sulphide  of  mercury 

Mercury 

0-86207 

Hg  S 

Hg 

Nickel 

Protoxide  of  nickel 

Nickel 

0-78667 

Ni  0 

. Ni 

Nitrogen 

Ammonio-bichloride  of  platinum 

Nitrogen 

0-06071 

N H4  CL  Pt  Cla 

N 

Platinum 

Nitrogen 

0 14155 

Pt 

N 

Sulphate  of  baryta 

Nitric  acid 

0-46352 

Ba  0,  S 03 

no5 

Cyanide  of  silver 

Cyanogen 

019410 

AgCaN 

C2  N 

Cyanide  of  silver 

Hydrocyanic  acid 

0-20156 

Ag  C2  N 

HC2N 

Oxygen 

Alumina 

Oxygen 

0-46602 

Ala  03 

03 

Teroxide  of  antimony 

Oxygen 

0-16438 

Sb  03 

03 

Arsenious  acid 

Oxygen 

0-24242 

As  03 

03 

Arsenic  acid 

Oxygen 

0-34783 

As  Or, 

o5 

Baryta 

Oxygen 

010458 

Ba  0 

0 

Teroxide  of  bismuth 

Oxygen 

0-10345 

Bi  03 

03 

Oxide  of  cadrhium 

Oxygen 

0-12500 

Cd  0 

0 

Sesquioxide  of  chromium 

Oxygen 

0-31381 

Cr2  03 

03 

Protoxide  of  cobalt 

Oxygen 

0-21333 

Co  0 

0 

TABLE  IV. 


615 


[continued). 


2 


1 *20001 
0-66700 

0- 72072 

1- 54930 
1-44105 
1-39241 
0*94040 
1-63218 

1- 26437 

2- 08000 
2-16000 
1-69880 
1-72414 
1-57333 
012542 
0-28310 
0-92704 
0*38820 
0-40312 
0-93204 
0-32877 
0-48484 
0-69565 
0-20915 
0-20690 
0-25000 
0 62762 
0-42667 


3 


1 -80091 

1- 00051 
1-08108 

2- 32394 
2-16157 
2-08861 

1- 41060 

2- 44828 

1- 89655 

3- 12000 
3-24000 

2- 54820 
2-58621 
2*36000 
0-18812 
0 42464 
1-39056 
0-58230 

0- 60468 

1- 39806 
0-49315 

0- 72726 

1- 04348 
0-31373 
0-31035 
0-37500 
0-94143 
0-64000 


4 


2-40121 

1- 33401 
1 -44144 
3 09859 

2- 88210 

2- 78481 
1-88080 

3- 26437 

2- 52874 

4- 16000 
4-32000 

3- 39760 
3-44828 
3-14667 
0-25083 

0- 56619 

1- 85408 
0-77640 

0- 80624 

1- 86408 
0-65754 

0- 96968 

1- 39130 
0-41830 
0-41380 

0- 50000 

1- 25524 
0-85333 


5 


3-00151 

1- 66751 
1 -80180 
3-87324 
3-60262 

I 

3- 48102 

2- 35099 

4- 08046 

3- 16092 

5- 20000 
5-40000 

4- 24701 
4-31034 
3-93333 
0-31354 
0-70774 
2-31760 

0- 97050 

1- 00780 

2- 33010 

0- 82192 

1- 21210 
1-73913 
0-52288 
0-51725 

0- 62500 

1- 56905 
j 1-06667 


6 


3- 60182 
2 00101 
2-16216 

4- 64789 
4-32314 
4-17722 

2- 82119 

4- 89655 

3- 79310 
6-24000 
6-48000 

5- 09641 
5-17241 

4- 72000 
0-37625 

0- 84929 
2-78111 

1- 16460 

1- 20936 

2- 79611 

0- 98630 

1- 45452 

2- 08696 
0-62745 
0-62070 

0- 75000 

1- 88286 
1-28000 


7 


4- 20212 
2-33451 

2- 52252 

5- 42254 
5 04367 

4- 87342 

3- 29139 

5- 71264 

4- 42529 
7-28000 
7-56000 

5- 94581 

6- 03448 
5-50667 
0-43896 

0- 99084 
3-24463 

1- 35870 
1-41092 
3-26213 
1-15069 

1- 69694 

2- 43478 
0-73203 
0-72415 

0- 87500 
2-19667 

1- 49333 


j 

8 


4- 80242 
2-66802 
2-88288 
619718 

5- 76419 

5- 56962 
3-76159 

6- 52874 

5 05747 
8-32000 
8-64000 
6-79521 
6-89655 

6 29334 

0- 50166 

1- 13238 
3-70815 
1 -55280 
1-61248 
3-72815 
1-31507 

1- 93936 

2- 78261 
0-83660 

0- 82760 

1- 00000 
2-51048 
1-70666 


9 


5- 40273 
3 00152 

3- 24324 

6- 97183 
6-48472 

6- 26583 

4- 23179 
7*34483 

5- 68966 
9-36000 
9-72000 

7- 64461 
7-75862 
7-08000 

0- 56437 

1- 27393 
417167 
1-74690 
1-81404 
4-19417 

1- 47946 

2- 18178 

3- 13043 

0- 94118 
0 93105 

1- 12500 

2- 82429 
1-92000 


616 


TABLE  IV. 


TABLE  IV. 


Elements. 

Found. 

Sought. 

1 

Oxygen 

Oxide  of  copper 

Oxygen 

0-20151 

Cu  0 

0 

Protoxide  of  iron 

Oxygen 

0-22222 

Fe  0 

0 

Sesquioxide  of  iron 

Oxygen 

0-30000 

Fe2  O3 

03 

Oxide  of  lead 

Oxygen 

0 07175 

Pb  0 

0 

Lime 

Oxygen 

0-28571 

Ca  0 

0 

Magnesia 

Oxygen 

0-39970 

Mg  0 

0 

Protoxide  of  manganese 

Oxygen 

0-22535 

MnO 

0 

Protosesquioxide  of  manganese 

Oxygen 

0-27947 

Mn  0 -j-  Mn2  O3 

o4 

Sesquioxide  of  manganese 

Oxygen 

0-30380 

Mn2  03 

- 03 

Suboxide  of  mercury 

Oxygen 

0-03846 

Hg20 

0 

Oxide  of  mercury 

Oxygen 

0 07407 

HgO 

0 

Protoxide  of  nickel 

Oxygen 

0-21333 

M 0 

0 

Potassa 

Oxygen 

0-16982 

K 0 

0 

Silicic  acid 

Oxygen 

0*53333 

Si  02 

o2 

Oxide  of  silver 

Oxygen 

0-06898 

AgO 

0 

Soda 

Oxygen 

0-25810 

Na  0 

0 

Strontia 

Oxygen 

015459 

Sr  0 

0 

Binoxide  of  tin 

Oxygen 

0-21333 

Sn  02 

o2 

Water 

Oxygen 

0-88889 

HO 

0 

Oxide  of  zinc 

Oxygen 

0 19740 

Zn  0 

0 

Phosphorus. . 

Phosphoric  acid 

Phosphorus 

0*43662 

P05 

P 

Pyrophosphate  of  magnesia 

Phosphoric  acid 

0-63964 

2 Mg  0,  P 05 

P05 

Phosphate  of  sesquioxide  of  iron 

Phosphoric  acid 

0-47020 

Fe2  03,  P 05 

P05 

Phosphate  of  silver 

Phosphoric  acid 

0-16949 

3 Ag  0,  P 06 

P05 

Phosphate  of  sesquioxide  of  uranium 

Phosphoric  acid 

019910 

2 Ur2  03,  P 05 

P05 

Pyrophosphate  of  silver 

Phosphoric  acid 

0 23437 

2 Ag  0,  P 05 

P05 

Potassium. . . 

Potassa 

Potassium 

0-83018 

K 0 

K 

Sulphate  of  potassa 

Potassa 

0-54080 

K 0,  S Oa 

KO 

TABLE  IV. 


617 


{continued). 


2 

3 

4 

i 

5 

6 

I 

7 

8 

9 

0-40302 

0-60453 

0-80604 

1-00756 

1 -20907 

1-41058 

1-61209 

1-81360 

0-44444 

0.66667 

0-88889 

111111 

1-33333 

1-55555 

1-77778 

2-00000 

0-60000 

0-90000 

1-20000 

1-50000 

1-80000 

2-10000 

2-40000 

2-70000 

0-14350 

0 21525 

0-28700 

0-35874 

0-43049 

0-50224 

0-57399 

0-64574 

0-57143 

0-85714 

1-14286 

1 -42857 

1-71429 

2-00000 

2-28571 

2-57143 

0-79939 

1-19909 

1 -59879 

1-99849 

2-39818 

2-79788 

3-19758 

3-59727 

0-45070 

0 67606 

0-90141 

1 -12676 

1-35211 

1 -57746 

1-80282 

2-02817 

0-55895 

0-83843 

1-11790 

1 -39738 

1-67686 

1-95633 

2-23581 

2-51528 

0-60759 

0-91139 

1-21519 

1-51899 

1 -82278 

2-12658 

2-43038 

2-73417 

0-07692 

0-11539 

0-15385 

0-19231 

0-23077 

0-26923 

0-30770 

0-34616 

0-14815 

0-22222 

0-29630 

0-37037 

0-44444 

0-51852 

0-59259 

0-66667 

0-42667 

0-64000 

0-85333 

1 -06667 

1-28000 

1 '49333 

1 -70667 

1-92000 

0-33964 

0-50946 

0-67928 

0-84910 

1-01892 

1-18874 

1-35856 

1 -52838 

1 -06667 

1-60000 

2-13333 

2-66667 

3-20000 

3-73333 

4-26667 

4-80000 

0-13796 

0-20694 

0-27592 

0-34490 

0-41388 

0-48286 

0-55184 

0-62082 

0-51621 

0-77431 

1-03242 

1 -29052 

1-54863 

1-80673 

2-06484 

2-32294 

0-30918 

0-46377 

0-61836 

0-77295 

0-92753 

1-08212 

1 -23671 

1-39130 

0 42667 

0-64000 

0-85333 

1-06667 

1-28000 

1-49333 

1-70667 

1-92000 

1-77778 

2-66667 

3-55556 

4-44445 

5-33333 

6-22222 

7-11111 

8-00000 

0-39480 

0-59220 

0-78960 

0-98700 

1-18440 

1-38180 

1 -57920 

1-77660 

0*87324 

1 -30986 

1-74648 

2-18309 

2-61971 

3 05633 

3-49295 

3-92957 

1-27928 

1-91892 

2-55856 

3-19820 

3-83784 

4-47748 

5-11712 

5-75676 

0-94040 

1-41060 

1-88080 

2-35099 

2-82119 

3-29139 

3-76159 

4-23179 

0-33898 

0-50847 

0-67796 

0-84745 

1-01694 

1-18643 

1-35592 

1-52541 

0-39821 

0-59731 

0-79641 

0-99551 

1-19462 

1-39372 

1-59282 

1-79192 

0-46874 

0-70311 

0 93748 

1-17185 

1 -40622 

1-64059 

1-87496 

2-10933 

1-66036 

2-49054 

3-32072 

415090 

4-98108 

5-81126 

6-64144 

7-47162 

1-08161 

1-62241 

216321 

2-70402 

3-24482 

3-78563 

4-32643 

4-86723 

618 


TABLE  IV. 


TABLE  IV. 


Elements. 

Found. 

Sought. 

1 

Potassium. . . 

Chloride  of  potassium 

Potassium 

0*52445 

K Cl 

K 

Chloride  of  potassium 

Potassa 

0-63173 

K Cl 

K 0 

Potassio -bichloride  of  platinum 

Potassa 

0-19272 

K Cl,  Pt  Cl2 

K 0 

Potassio-bichloride  of  platinum 

Chloride  of  potassium 

0-30507 

K Cl,  Pt  Cl2  i 

K Cl 

Silicon 

Silicic  acid 

Silicon 

0-46667 

Si  02 

Si 

Silver 

Chloride  of  silver 

Silver 

0-75276 

Ag  Cl 

A g 

Chloride  of  silver 

Oxide  of  silver 

0-80854 

A g Cl 

A g 0 

Sodium 

Soda 

Sodium 

0-74190 

Na  0 

Na 

Sulphate  of  soda 

Soda 

0-43658 

Na  0,  S 03 

Na  0 

Chloride  of  sodium 

Soda 

0-53022 

Na  Cl 

Na  0 

Chloride  of  Sodium 

Sodium 

0-39337 

Na  Cl 

Na 

Carbonate  of  soda 

Soda 

0-58487 

Na  0,  C 02 

Na  0 

Strontium. . . 

Strontia 

Strontium 

0-84541 

SrO 

Sr 

Sulphate  of  strontia 

Strontia 

0-5640^ 

Sr  0,  S 03 

Sr  0 

Carbonate  of  strontia 

Strontia 

0-70169 

Sr  0,  C 02 

SrO 

Sulphur 

Sulphate  of  baryta 

Sulphur 

0-13734 

Ba  0,  S 03 

S 

Tersulphide  of  arsenic 

Sulphur 

0-39024 

As  S3 

S3 

Sulphate  of  baryta 

Sulphuric  acid 

0-34335 

Ba  0,  S O3 

S03 

Tin 

Binoxide  of  tin 

Tin 

0-78667 

Sn  02 

Sn 

Binoxide  of  tin 

Protoxide  of  tin 

0*89333 

Sn  02 

Sn  0 

Zinc 

Oxide  of  zinc 

Zinc 

0-80260 

Zn  0 

Zn 

Sulphide  of  zinc 

Oxide  of  zinc 

0-83515 

Zn  S 

Zn  0 

Sulphide  of  zinc 

Zinc 

0-67031 

Zn  S 

Zn 

TABLE  IV. 


619 


( continued \ 


23456789 


3-67114 


1-04890 

1-26346 

0 38545 

0-61015 

0- 93333 

1- 50552 

1-61708 

1-48379 

0- 87316 

1- 06043 

0- 78673 

1- 16974 

1-69082 

1 -12807 

1-40339 

0-27468 

0-78049 

0- 68670 

1- 57333 

1-78667 

1-60520 

1-67031 

1-34061 


1-57335 

1-89519 

0-57817 

0- 91522 

1- 40001 

2- 25828 

2-42562 

2-22569 

1-30975 

1-59065 
1 -18009 

1- 75460 

2- 53623 

1- 69210 

2- 10508 

0- 41202 

1- 17073 

1- 03004 

2- 36000 

2-68000 

2-40780 

2-50546 

2-01092 


2- 09780 
252692 

0- 77090 
1 -22030 
1 -86667 

3- 01104 

3-23416 

2-96758 

1- 74633 

2- 12086 

1- 57346 

2- 33947 

3- 38164 

2-25613 

2- 80678 

0- 54936 

1- 56097 

1- 37339 

3- 14667 

3-57333 

3-21040 

3-34062 

2- 68123 


2- 62225 

3- 15865 

0- 96362 

1- 52537 

2- 33333 

3- 76380 

4- 04270 

3- 70948 

2-18291 

2-65108 

1- 96683 

2- 92434 

4- 22705 

2- 82017 

3- 50848 

0- 68670 

1- 95122 
1-71674 

3- 93333 

4- 46667 

4-01300 

4-17577 

3-35154 


3*14669 

3- 79037 
1 15634 

1- 83044 

2- 80000 

4- 51656 

4-85124 

4-45137 

2-61949 
318130 

2- 36019 

3- 50921 
5 07247 

3- 38420 

4- 21017 

0-82403 

2-34146 

2-06009 

4- 72000 

5- 36000 

4- 81560 

5- 01092 

4-02184 


4- 42210 

1- 34907 
2 13552 

3-26667 

5- 26982 

5-65978 

5-19327 

3-05607 

3- 71151 

2- 75356 

4- 09407 

5- 91788 

3- 94823 

4- 91186 

0-96137 

2-73170 
2-40344 

5- 50667 

6- 25333 

5-61820 

5-84608 

4-69215 


4- 19559 
5*05383 

1- 54179 

2- 44059 

3- 73333 

6-02208 

6-46832 

5- 93516 

3- 49265 

4- 24173 

3- 14692 

4- 67894 

6- 76329 

4- 51226 

5- 61356 

1- 09871 

3-12194 

2- 74678 

6- 29334 
7*14666 

6-42080 

6-68123 

5-36246 


4- 72004 

5- 68556 

1- 73452 

2- 74567 

4- 20000 

6- 77484 

7- 27686 

6- 67706 

3- 92924 

4- 77194 

3-54029 

5- 26381 

7- 60870 

5- 07630 

6- 31526 
1 *23605 

3-51219 

3-09013 

7- 08000 

8- 04000 

7-22340 

7-51639 

6-03276 


620 


TABLES  V. — VL 


TABLE  Y. 


SPECIFIC  GRAVITY  AND  ABSOLUTE  WEIGHT  OF  SEVERAL  GASES. 


Specific  gravity,  atmos- 
pheric air  = 1 -0000. 

1 litre  (1000  cubic  centi- 
metres) of  gas  at  0°  and  0-76 
metre  bar.  pressure  weighs 
grammes. 

Atmospheric  air 

1-0000 

1 -29366 

Oxygen 

1-10832 

1 -43379J 
0-08961 

Hydrogen , 

0-06927 

Water,  vapor  of 

0-62343 

0-80651 

Carbon,  vapor  of 

0-83124 

1 -07534 

Carbonic  acid 

1 -52394 

1 -97146 

Carbonic  oxide 

0-96978 

1 -25456 

Marsh  gas 

0-55416 

0-71689 

Elayl  gas  

0-96978 

1 -25456 

Phosphorus,  vapor  of. 

4-29474 

5-55593 

Sulphur,  vapor  of 

6-64992 

8-60273 

Hydrosulphuric  acid 

1-17759 

1 -52340 

Iodine,  vapor  of. 

8-78898 

11-36995 

Bromine,  vapor  of 

5 -53952 

7-16625 

Chlorine 

Nitrogen 

Ammonia 

2-45631 

0-96978 

0-58879 

3-17763 
1 -25456 
0 76169 

Cyanogen 

1-80102 

2-32991 

/ 

■ TABLE  YI. 


COMPARISON  OF  THE  DEGREES  OF  THE  MERCURIAL  THERMOMETER  WITH 
THOSE  OF  THE  AIR  THERMOMETER. 


According  to  Magnus. 


Degrees  of  the  mercurial 
thermometer. 


Degrees  of  the  air 
thermometer. 


100  100-00 

150  148-74 

200  197-49 

250  245-39 

300  294-51 

330  320  92 


EDITOR’S  APPENDIX. 


CORRECTION  OF  THE  VOLUME  OF  GASES. 

Dr.  Gibbs’  method  of  finding  at  once  the  total  correction  for  tempera- 
ture, pressure , and  moisture  in  absolute  determinations  of  nitrogen , or 
other  gases  : — * 

u I take  a graduated  tube,  which  I fill  with  mercury,  then  displace 
about  two-thirds  of  the  mercury  with  air,  and  invert  the  tube  into  a cis- 
tern of  mercury.  Then  I make  four  or  five  determinations  of  the  volume 
of  the  included  (moist)  air  in  the  usual  manner,  and  find  the  volume 
of  the  air  at  0°  and  760mm  as  a mean  of  all  the  determinations.  This 
tube  I call  the  companion  tube,  and  it  always  hangs  in  the  little  room 
I use  for  gas  analyses.  Suppose  the  volume  of  (dry)  air  at  0°  and  760mra 
is  132.35  c.c. 

“ Now,  in  making  an  absolute  nitrogen  determination  I collect  the 
nitrogen  moist  over  mercury  in  a graduated  tube,  and  then  suspend  the 
measuring  tube  by  the  side  of  the  companion  tube.  I then  by  a cord 
and  pulley  bring  the  level  of  the  mercury  in  the  two  tubes  to  correspond 
exactly,  and  then  read  off  the  volume  of  air  in  the  companion  tube  and 
the  volume  of  nitrogen  in  the  measuring  tube.  I ought  to  have  stated 
that  the  two  tubes  hang  in  the  same  cistern  of  mercury.  Suppose  the 
volume  of  air  in  the  companion  tube  to  be  143  c.c. ; then  the  total  cor- 
rection for  temperature,  pressure  and  moisture  will  be  143  — 132*35  = 
10-65  c.c.  The  correction  for  the  nitrogen  will  then  be  found  by  Rule 
of  Three.  As  the  observed  volume  of  air  in  the  companion  tube  is  to 
the  observed  volume  of  nitrogen,  so  is  (in  this  case)  10 -65  to  the  re- 
quired correction.  In  this  way,  when  the  volume  of  air  in  the  com- 
panion tube  is  once  found,  no  further  observations  of  temperature , pres- 
sure, or  height  of  mercury  above  the  mercury  in  the  cistern  are  necessary. 
The  companion  tube  lasts  for  an  indefinite  time.  I have  even  used  it 
filled  with  water,  without  any  appreciable  change  in  some  weeks,  but  I 
prefer  mercury.  As  the  two  tubes  hang  side  by  side,  there  is  never  an 
appreciable  difference  of  temperature.  My  results  are  most  satisfactory. 
Williamson  & Russell  have,  as  you  know,  used  a companion  tube 
for  equating  pressures , but  not  for  • finding  the  total  value  of  the  tem- 
perature and  pressure  correction  at  once ; and  I believe  that  my  process 
is  wholly  new.  Certainly  it  is  wonderfully  convenient,  and  saves  all 
tables  and  labor  of  computation.” 

ASSAY  OF  CHROMIC  IRON. 

Mix  the  pulverized  ore  in  a platinum  vessel  with  three  parts  of  pul- 
verized and  pure  cryolite ; upon  the  top  of  the  mixture  place  twelve 


* Private  communication. 


622 


editor’s  appendix. 


parts  of  bisulphate  of  potassa,  or  of  soda ; heat,  cautiously  at  first,  to 
fusion,  for  fifteen  minutes ; digest  the  cold  fused  mass  with  a little 
strong  hydrochloric  acid,  for  ten  minutes — (so  far  Gibbs  and  Clarke, 
Am.  Jour.  Sci .,  2d  ser.,  xlv.,  178);  add  a few  drops  of  alcohol  to 
reduce  any  chromic  acid  ; dilute  with  water,  and  add  cautiously  chloride 
of  barium  until  all  sulphuric  acid  is  precipitated.  Filter  : concentrate 
the  filtrate  to  a small  bulk  in  a porcelain  capsule ; add  (according  to 
Storer  and  Pearson,  Am.  Jour.  Sci.,  2d  ser.,  xlviii.,  pp.  198-200) 
nitric  acid  and  crystals  of  chlorate  of  potash,  and  maintain  the  heat 
(covering  the  capsule  with  an  inverted  funnel)  until  the  chromium  is  all 
oxidized  to  chromic  acid  ; add,  if  needful,  more  chloride  of  barium,  to 
convert  the  chromic  acid  into  chromate  of  barium  ; evaporate  off  the 
great  excess  of  acid  ; dilute.  Allow  the  precipitate  to  subside  ; decant 
the  clear  liquid  into  a filter  ; wash  the  precipitate  by  decantation 
with  solution  of  acetate  of  ammonia,  finally  transferring  it  to  the  filter  ; 
dry ; ignite  gently  apart  from  the  filter,  and  weigh  the  chromate  of 
baryta. 

Note. — The  above  scheme,  as  yet  untried  by  the  Editor,  is  simply  proposed 
as  an  attempt  to  combine  the  best  points  in  the  two  valuable  communications 
referred  to,  with  a view  to  make  a rapid  method  for  estimating  chromium  in  its 
ore.  The  observation  of  Storer  and  Pearson  in  the  paper  above  cited  (p.  200, 
paragraph  v.),  promises  a still  better  method,  which  deserves  elaboration. 

SEPARATION  OF  PHOSPHORIC  ACID  FROM  LIME,  ALUMINA,  AND  OXIDE  OF 

LIME. 

In  absence  of  sulphuric  acid,  Brassier  (Ann.  Chim.  JPhys.  [4]  vii., 
355)  dissolves  the  phosphates  in  hydrochloric  acid,  adds  ammonia  in 
excess,  and  re-dissolves  the  precipitated  phosphates  by  additions  of  citric 
acid,  keeping  the  liquid  ammoniacal.  From  the  solution  thus  obtained, 
tlie  phosphoric  acid  is  thrown  down  by  chloride  of  magnesium,  as  pure 
ammonio-magnesian  phosphate.  Since  the  latter  is  sensibly  soluble  in 
citrate  of  ammonia,  the  citric  acid  solution  should  be  added,  drop  by 
drop,  avoiding  an  excess.  The  chloride  of  magnesium  should  be  free 
from  sulphuric  acid,  otherwise  sulphate  of  lime  would  also  be  precipi- 
tated. It  is  to  be  expected  that  the  results  will  fall  out  too  low  in 
presence  of  much  iron  or  alumina  (see  p.  276,  a),  but  the  method  is  very 
convenient  for  the  analysis  of  bone-black  and  many  native  phosphates. 


ALPHABETICAL  INDEX. 


PAGE 

Acetic  Acid  (reagent),  see  Qual.  Anal. 

table  of  specific  gravity 491 

Acidimetry 487 

Air,  analysis  of  atmospheric 553 

Alcohol  (reagent),  see  Qual.  Anal. 

Alkalimetry  498 

Alumina 113 

basic  acetate 113 

formiate.  .• 113 

estimation 174 

hydrate 112 

separation  from  alkalies 350 

alkaline  earths 350 

sesquioxide  of  chromium 354 

Ammonia  (reagent),  see  Qual.  Anal. 

•arsenio-molybdate , 139 

carbonate  (reagent),  see  Qual.  Anal.,  and 88,  90 

estimation  150 

molybdate  (reagent),  see  Qual.  Anal. 

s nitrate  (reagent) 91 

oxalate  (reagent),  see  Qual.  Anal. 

phospho-molybdate 143 

separation  from  other  alkalies 341 

succinate  (reagent) 87 

table  of  specific  gravity  of  solutions 498 

Ammonium,  chloride. ...  105 

(reagent),  see  Qual.  Anal.,  and 87,  91 

sulphide  (reagent),  see  Qual.  Anal. 

Analysis,  gravimetric 1 

quantitative 1 — 5,  40 

volumetric 2,  80 

Antimony 136 

antimoniate  of  teroxide  (antimonious  acid) 136 

estimation 341 

separation  from  bases  of  groups  I. — V 387 

other  metals  of  group  VI 397 

sulphides 135 

teroxide,  separation  from  antimonic  acid 402 

Anvil 34 

Aqua  regia  (reagent),  see  Qual.  Anal. 

Arsenic,  estimation 249 

separation  from  bases  of  groups  I. — V 388 

other  metals  of  group  VI 397 

tersulphide 138 

Arsenious  acid  (reagent)  95 

and  arsenic  acids,  separation  from  each  other 399 

other  acids  of  group  I . . . . 402 — 408 
Azotome  ter 159 


624 


INDEX. 


PAGE 

Balance 9 14 

Barium  chloride  (reagent) 88 

silicofluoride 107 

Baryta  (reagent) 1 86 

acetate  (reagent) 88 

carbonate 107 

(reagent),  see  Qual.  Anal.,  and 89 

estimation 164 

hydrate  (reagent) 90 

separation  from  alkalies 344 

other  alkaline  earths 346 

sulphate 106 

Baths,  air- 38 

paraffin- 40 

water- 37,  49 

Bismuth  basic  nitrate 132 

carbonate 132 

chromate 132 

estimation 232 

separation  from  base  of  groups  I. — IV 375 

other  bases  of  group  V 379 

teroxide 131 

tersulphide 132 

Bone  black,  analysis 550 

dust,  analysis 547 

Boracic  acid,  estimation 279 

separation  from  bases 281 

other  acids  of  group  I .402—408 

Bromine,  estimation  of  H Br 309 

free 311 

separation  from  acids  of  group  1 409 

chlorine  and  iodine 412 — 417 

metals 311 

Bunsen  burner 49 

Bunsen’s  pump 70,  79 

Burettes 27 — 32 

Cadmium  carbonate 133 

estimation 235 

oxide 133 

separation  from  bases  of  groups  I. — IV 375 

other  bases  of  group  V . 379 

sulphide 133 

Calcium  chloride  (reagent),  see  Qual.  Anal.,  and 89,  100 

fluoride 145 

Calculation  of  analyses 458 

tables  for 603 

Carbonic  acid  estimation 285 

separation  from  bases 287 

other  acids  of  group  1 402—408 

Chloric  acid  estimation 335 

separation  from  other  acids 418 

Chlorimetry 504 

Chlorine  (reagent),  see  Qual.  Anal.,  and 91 

estimation  of  H Cl 304 

of  free 307 

separation  from  acids  of  group  1 438 

bromine  and  iodine 414—416 

metals 306 

Chromic  acid  estimation 257 

separation  from  bases 261 

other  acids  of  group  1 402—408 

iron,  analysis 365 — 621 


INDEX. 


625 


PACK 

Chromium,  sesquioxide 114 

estimation 176 

separation  from  alkalies 350 

alkaline  earths 354 

alumina 354 

hydrated 114 

Clip 28 

Cobalt 120 

estimation ; 189 

hydrated  protoxide 119 

protoxide 120 

separation  from  alkalies 355 

alkaline  earths 356 

bases  of  group  III 359 

other  bases  of  group  IY 359 

sesquioxide 120 

and  potassa,  nitrite 121 

sulphate 120 

sulphide 120 

Compression-cock 28 

Cone,  platinum 70 

Copper 129 

(reagent) / 99 

estimation 225 

in  ores 525 

oxide 129 

(reagent) 96 

separation  from  bases  of  groups  I. — IV 375 

other  bases  of  group  V 379 

suboxide 131 

subsulphide 131 

subsulphocyanide 131 

sulphide 130 

Crucibles,  platinum. 63 

Crucible  tongs 65 

Cupellation 580 

Cyanogen  estimation 316 

separation  from  acids  of  group  1 409 

chlorine,  bromine,  and  iodine 449 

metals 317 

Cylinder,  graduated 28 

Decantation 55 

and  filtration. 60 

Decinormal  solutions 77 

Desiccators 36 

Determination  of  bodies 148 

Dolomite  analysis 518 

Drying 34 — 40 

of  filters 62 

of  precipitates 61 

-tube,  Liebig’s 38 

Elements  considered  in  this  work. 5 

Elutriation 33 

Equivalents,  table  of 603 

of  organic  bodies,  determination 452 

Erdmann’s  float 30 

Estimation  of  bodies 149 

Ether  (reagent) 83 

Evaporation 49 — 53 

Exercises 564 

Experiments 581 


626 


INDEX. 


PAGE 

Ferric yanogen  estimation 319 

separation  of  H3  Cfdy  from  H Cl 417 

Ferrocyanogen  estimation 319 

separation  of  H2  Cfy  from  H Cl 417 

Filter-ash  estimation 62 

paper ., 56 

patterns i ....  i * i i . 56 

stands 57 

Filtration 55 — 59 

Bunsen’s  rapid  method 66,  79 

Fluorine  estimation 284 

separation  from  acids  of  group  1 402 — 408 

metals 284 

Formulae  empirical ; 468 

rational 471 

Funnels 56 

Gold 134 

assay 5 3 | 

estimation 237 

separation  from  bases  of  groups  I. — V 387 

other  metals  of  group  VI 397 

tersulphide 134 

Guano,  analysis 545 

Gunpowder,  analysis 514 

residues,  analysis 411 

Hydriodic  acid,  see  Iodine. 

Hydrobromic  acid,  see  Bromine. 

Hydrochloric  acid  (reagent) 84 

table  of  sp.  gr.  of  solution. 489 

see  Chlorine. 

Hydrocyanic  acid,  see  Cyanogen. 

Hydrofluoric  acid  (reagent) 85 

see  Fluorine. 

Hydrofluosilicic  acid  (reagent),  see  Qual.  Anal. 

estimation 269 

Hydrogen  gas  (reagent) 91 

Hydrosulphuric  acid  (reagent),  see  Qual.  Anal. 
see  Sulphur. 

Hydrosulphurous  acid,  estimation 263 

Ignition  of  precipitates 62 — 66 

Bunsen’s  new  method 77 

residues  on  evaporation 53 

Iodic  acid  estimation 263 

Iodine  (reagent) 94 

estimation  of  H 1 311 

free 313 

separation  from  acids  of  group  1 409 

chlorine  and  bromine 414 — 416 

metals 313 

Iron,  analysis  of  cast  and  wrought 536 

separation  from  alkalies 355 

alkaline  earths 357 

bases  of  group  III 359 

other  bases  of  group  IV 359 

Iron,  sesquichloride  (reagent),  see  Qual.  Anal. 

sesquioxide 121 

arseniate 139 

basic  acetate 123 

basic  formiate 123 

basic  phosphate 140 


INDEX. 


627 


PAGE 

Iron,  sesquioxide  estimation 199 

hydrate 121 

succinate 123 

and  ammonio-sulphate  (reagent)  93 

ores,  analysis 524 

protoxide,  estimation 192 

and  ammonia,  sulphate  (reagent) 93 

separation  from  sesquioxide §68 

sulphate  (reagent),  see  Qual.  Anal. 

sulphide 122 

Lead,  acetate  (reagent),  see  Qual.  Anal. 

arseniate 137 

carbonate 125 

chromate  140 

(reagent) 97 

estimation 216 

oxalate 126 

oxide  126 

(reagent) 87 

phosphate 140 

separation  from  bases  of  groups  I. — IV 375 

other  bases  of  group  V 379 

sulphate . 126 

sulphide 127 

Levigation 33 

Lime  (reagent) . 86 

carbonate 109 

chloride,  valuation 504 

estimation 168 

oxalate 109 

separation  from  alkalies 344 

other  alkaline  earths 346 

-stone,  analysis 518 

sulphate..., 108 

superphosphate,  analysis 548 

Lithia,  estimation 161 

separation  from  other  alkalies 342 

Litmus, ' tincture 92 

Loss  and  excess,  &c 466 

Magnesia 112 

and  ammonia,  arseniate 138 

phosphate Ill 

basic  phosphate 140 

estimation 171 

-mixture 89 

pyrophosphate Ill 

separation  from  alkalies 344 

other  alkaline  earths 347 

sulphate Ill 

(reagent),  see  Qual.  Anal. 

Manganese,  ammonio-phosphate 118 

binoxide 117 

valuation  of  commercial 508 

carbonate 116 

estimation 182 

hydrated  protoxide 117 

pyrophosphate 118 

protosesquioxide 117 

separation  from  alkalies 356 

alkaline  earths 357 

bases  of  group  III 359 


628 


INDEX. 


PASS 

Manganese,  separation  from  other  bases  of  group  IV 359 

sulphide 117 

Manures,  analysis ", 543 

Marls,  analysis 318 

Measuring  of  liquids 22—32 

of  gases 19 — 22 

flasks 22 

tubes  for  gases 19 

Meniscus,  error  of 21 

Mercury 127 

chloride  (reagent),  see  Qual.  Anal. 

oxide 129 

estimation 222 

separation  from  suboxide 379 

separation  from  bases  of  groups  I. — IY 375 

other  bases  of  group  Y 379 

subchloride 128 

suboxide,  estimation 220 

sulphide 128 

Moisture . ...  34 

Molybdic  acid,  estimation 255 

Mortar,  agate 33 

steel 32 

Nickel,  estimation 187 

protoxide 119 

hydrate....; 118 

separation  from  alkalies 355 

alkaline  earths 356 

bases  of  group  III 359 

other  bases  of  group  IY 359 

sesquioxide 119 

sulphide,  hydrated 119 

Nitric  acid  (reagent) 84 

estimation 328 

separation  from  bases 328 

other  acids 418 

table  of  specific  gravity  of  solution 490 

Nitrogen  gas 106 

Dr.  Gibbs’  method  of  measuring 621 

Nitrous  acid,  estimation 263 

Normal  solutions 80 

Organic  Analysis,  see  Table  of  Contents xiii 

bodies,  determination  of  equivalent  of 452 

Oxalic  acid  (reagent') . 92 

estimation 282 

separation  from  bases 283 

other  acids  of  group  1 402 — 408 

Oxygen  gas  (reagent) 97 

Palladium,  estimation 236 

prctiodide 147 

sodio-protochloride  (reagent),  see  Qual.  Anal. 

Phosphoric  acid,  estimation 269 

separation  from  bases 275 — 622 

other  acids  of  group  1 402 — 408 

Pinchcock 28 

Pipette 125 

Platinum 134 

amm  onio-bichloride 105 

bichloride  (reagent),  see  Qual.  Anal 

bisulphide 134 


INDEX. 


629 


Platinum  estimation 

potassio-bichloride 

separation  from  bases  of  groups  I. — V , 

other  metals  of  group  VI. . . 

sodio-bichloride 

Potash  (reagent) 

and  soda,  carbonates  (reagent),  see  Qual.  Anal. 

bichromate  (reagent)  see  Qual.  Anal,  and 

bisulphate 

(reagent) 

-bulbs,  Liebig’s 

estimation 

nitrate  (reagent),  see  Qual.  Anal. 
nitrite  (reagent),  see  Qual.  Anal. 

permanganate  (reagent) 

separation  from  other  alkalies 

sulphate 

(reagent),  see  Qual.  Anal. 

table  pf  specific  gravity  of  solution 

Potassium,  borofluoride 

chloride 

cyanide  (reagent),  see  Qual.  Anal. 

iodide  (reagent) 

Powdering 

Precipitation 


PAGE 

. 239 
. 103 
. 387 
. 397 
. 105 
86,  99 

. 100 
. 102 
. 90 

. 425 
. 151 


92 

339 

102 

497 

144 

103 

95 

32 

53 


Salt,  analysis  of  common 514 

Sample,  selection  of 31 

Selenic  acid,  separation  from  sulphuric  acid,  see  Note 403 

Selenious  acid,  estimation 261 

Separation  of  bodies 337 

Fe,03,Al,03,  Mn  O,  Ca  O,  Mg  O,  K O,  and  Na  0 370 

Sifting 33 

Silica 145 

estimation 299 

hydrated 145 

separation  from  other  acids  of  group  1 402-408 

bases 299 

Silicates,  analysis  of  native 516 

Silver  . . 124 

(reagent) 96 

bromide 146 

chloride 124 

cyanide 125 

estimation 205 

in  galena 528 

iodide 147 

nitrate  (reagent),  see  Qual.  Anal. 

phosphate,  tribasic 143 

separation  from  bases  of  groups  I. — IV 375 

other  bases  of  group  V 379 

sulphide 125 

Soda  (reagent) 86 

acetate  (reagent),  see  Qual.  Anal. 

biborate  (reagent) 90 

bisulphate 104 

bisulphite  (reagent),  see  Qual.  Anal. 

carbohate ; 104 

(reagent) 88,  90 

estimation 154 

hyposulphite  (reagent) 88 

-lime  (reagent) 98 

nitrate  (reagent)  see  Qual.  Anal. 


630 


INDEX. 


Soda  phosphate  (reagent),  see  Qual.  Anal. 

separation  from  other  alkalies 339 

sulphate 104 

table  of  specific  gravity  of  solution 497 

Sodium,  chloride 104 

(reagent) 95 

sulphide  (reagent),  see  Qual.  Anal. 

Solution 46 

Standard  solutions 80 

Steel,  analysis 536 

Strontia,  carbonate 108 

estimation 166 

separation  from  alkalies 344 

other  alkaline  earths " 346 

sulphate 108 

Strontium,  chloride  (reagent) 89 

Sulphur,  estimation  of  H S 321 

separation  of  H S from  acids  of  group  1 409-411 

hydrochloric  acid 418 

from  metals 323 

Sulphuric  acid  (reagent),  see  Qual.  Anal. 

estimation 264 

separation  from  bases 268 

other  acids  of  group  1 402-408 

table  of  specific  gravity  of  solutions 488 

Sulphurous  acid,  estimation 262 

Superphosphate,  analysis 548 

Synopsis  of  the  work 6 


Tartaric  acid  (reagent),  see  Qual.  Anal. 

Tin,  binoxide 136 

phosphate 142 

separation  from  protoxide 397 

estimation 245 

hydrated  bisulphide 137 

protosulphide 137 

protochloride  (reagent),  see  Qual.  Anal. 

separation  from  bases  of  groups  I.  — V 387 

other  metals  of  group  VI 397 

Titanic  acid,  estimation 178 

Triangle,  platinum. . * 64 

Uranium,  estimation 205 

separation  from  bases  of  groups  I. — IY 373 

sesquioxide,  acetate  (reagent) 89 

phosphate 142 

Vapor-density,  determination 453 

Washing-bottles 56 

of  precipitates 59 

Watch-glasses,  clasp  for 37 

Water,  analysis  of  fresh 483 

distilled 83 

estimation  of 42 — 46 

Weighing 15 — 18 

off  of  substance ? 41 

of  residues  on  evaporation. ...  52 

Weights 14 

Zinc  (reagent) 86 

basic  carbonate 114 


INDEX. 


631 


PAGE 

Zinc  estimation 179 

ores,  assay. 634 

oxide 115 

separation  from  alkalies 355 

alkaline  earths 357 

bases  of  group  III 359 

other  bases  of  group  IY 359 

sulphide 115 


r 


TABLE  OF  ATOMIC  WEIGHTS, 

Prep?  " 4 fq  the  Use  of  the  Students  of  the  School  of  Mines, 
Columbia  College,  Jan.,  .872. 


BY  C.  F.  CHANDLER,  PH.  D. 


Hydrogen,  = 1. 


Oxygen, 

0., 

Old. 

8- 

New. 

16- 

Oxygen, 

O. 

Old. 

8* 

New. 

16- 

Aluminium, 

Al. 

13  "7 

27-4 

Mercury, 

Hg. 

ICO* 

200- 

Antimony , 

£6. 

122- 

122* 

Molybdenum, 

Mo 

48- 

96- 

Arsenic , 

As. 

75* 

75- 

Nickel, 

Ni. 

29- 

58- 

Barium, 

Ba.’ 

68  '5 

137- 

Nitrogen , 

N. 

14* 

14- 

Bismuth , 

Bi. 

210- 

210- 

Osmium, 

Os. 

ioc- 

200- 

Boron , 

B. 

IP 

11* 

Oxygen, 

O. 

s' 

16- 

Bromine , 

Br. 

80- 

80* 

Palladium, 

Pd. 

53- 

106- 

Cadmium, 

Cd. 

56- 

112* 

Phosphorus , 

P. 

31- 

31- 

Ca>sium, 

Cs. 

133* 

133* 

Platinum, 

Pt. 

98-7 

197-4 

Calcium, 

Ca. 

20- 

40* 

Potassium , 

K. 

39-1 

39-1 

Carbon, 

C. 

6* 

12* 

Rhodium 

Ro. 

52- 

104- 

Cerium, 

Ce. 

45-7 

91*3 

Rubidium , 

Rb. 

85-4 

85-4 

Chlorine , 

Cl. 

35  5 

35-5 

Ruthenium, 

Ru. 

52- 

104- 

Chromium, 

Cr. 

264 

52-2 

Selenium, 

Se. 

39-5 

79- 

Cobalt, 

Co. 

30- 

60* 

Silicon, 

Si. 

14’ 

28- 

Columbium , 

Cb. 

94- 

94- 

Silver , 

Ag. 

108- 

108- 

Copper, 

Cu. 

31-7 

63-4 

Sodium , 

Na. 

23- 

23- 

Didymium, 

D. 

47-5 

95* 

Strontium, 

Sr. 

44- 

88- 

Erbium, 

E. 

56  3 

112-6 

Sulphur, 

S. 

16- 

32- 

Fluorine , 

F. 

19* 

19; 

Tantalum, 

To, 

182* 

182- 

Glucinum, 

Gl. 

46 

9-2 

Tellurium, 

Te. 

64- 

128- 

Gold , 

A u. 

197- 

197* 

Terbium, 

Tb. 

37-7 

75-4 

Hydrogen , 

H. 

1* 

1- 

Thallium, 

Tl. 

204- 

204- 

Indium, 

In. 

567 

113-4 

Thorium, 

Th. 

59-2 

118-4 

Iodine , 

/. 

127- 

127* 

Tin, 

Sn. 

59- 

118* 

Iridium, 

Ir. 

99- 

198* 

Titanium, 

Ti. 

25- 

50* 

Iron, 

Fe. 

28- 

56* 

Tungsten, 

W. 

92- 

184* 

Lanthanum, 

La. 

46- 

92* 

Uranium, 

U. 

60- 

120- 

Lead, 

Pb. 

103  5 

207* 

Vanadium, 

V. 

51-3 

51-3 

Lithium , 

Li. 

7’ 

7* 

Y ttrium, 

Y. 

30-8 

61-6 

Magnesium,  Mg. 

12- 

24- 

Zinc, 

Zn. 

32-5 

65- 

Manganese, 

Mn. 

27-5 

55* 

Zirconium, 

Zr. 

44-8 

89-6 

Note. — The  Perissads  are  printed  in  italics,  the  Artiads  in  Roman. 
To  convert  formula?  in  the  old  system  into  the  new,  double  the  atoms 
of  the  Perissads,  or  halve  the  atoms  of  the  Artiads,  and  vice  versa. 


